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<li><a class="reference internal" href="#">Memory Management</a><ul>
<li><a class="reference internal" href="#overview">Overview</a></li>
<li><a class="reference internal" href="#allocator-domains">Allocator Domains</a></li>
<li><a class="reference internal" href="#raw-memory-interface">Raw Memory Interface</a></li>
<li><a class="reference internal" href="#memory-interface">Memory Interface</a></li>
<li><a class="reference internal" href="#object-allocators">Object allocators</a></li>
<li><a class="reference internal" href="#default-memory-allocators">Default Memory Allocators</a></li>
<li><a class="reference internal" href="#customize-memory-allocators">Customize Memory Allocators</a></li>
<li><a class="reference internal" href="#debug-hooks-on-the-python-memory-allocators">Debug hooks on the Python memory allocators</a></li>
<li><a class="reference internal" href="#the-pymalloc-allocator">The pymalloc allocator</a><ul>
<li><a class="reference internal" href="#customize-pymalloc-arena-allocator">Customize pymalloc Arena Allocator</a></li>
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<li><a class="reference internal" href="#the-mimalloc-allocator">The mimalloc allocator</a></li>
<li><a class="reference internal" href="#tracemalloc-c-api">tracemalloc C API</a></li>
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<section id="memory-management">
<span id="memory"></span><h1>Memory Management<a class="headerlink" href="#memory-management" title="Link to this heading"></a></h1>
<section id="overview">
<span id="memoryoverview"></span><h2>Overview<a class="headerlink" href="#overview" title="Link to this heading"></a></h2>
<p>Memory management in Python involves a private heap containing all Python
objects and data structures. The management of this private heap is ensured
internally by the <em>Python memory manager</em>. The Python memory manager has
different components which deal with various dynamic storage management aspects,
like sharing, segmentation, preallocation or caching.</p>
<p>At the lowest level, a raw memory allocator ensures that there is enough room in
the private heap for storing all Python-related data by interacting with the
memory manager of the operating system. On top of the raw memory allocator,
several object-specific allocators operate on the same heap and implement
distinct memory management policies adapted to the peculiarities of every object
type. For example, integer objects are managed differently within the heap than
strings, tuples or dictionaries because integers imply different storage
requirements and speed/space tradeoffs. The Python memory manager thus delegates
some of the work to the object-specific allocators, but ensures that the latter
operate within the bounds of the private heap.</p>
<p>It is important to understand that the management of the Python heap is
performed by the interpreter itself and that the user has no control over it,
even if they regularly manipulate object pointers to memory blocks inside that
heap. The allocation of heap space for Python objects and other internal
buffers is performed on demand by the Python memory manager through the Python/C
API functions listed in this document.</p>
<p id="index-0">To avoid memory corruption, extension writers should never try to operate on
Python objects with the functions exported by the C library: <code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code>,
<code class="xref c c-func docutils literal notranslate"><span class="pre">calloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">realloc()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">free()</span></code>. This will result in mixed
calls between the C allocator and the Python memory manager with fatal
consequences, because they implement different algorithms and operate on
different heaps. However, one may safely allocate and release memory blocks
with the C library allocator for individual purposes, as shown in the following
example:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyObject</span><span class="w"> </span><span class="o">*</span><span class="n">res</span><span class="p">;</span>
<span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="w"> </span><span class="n">malloc</span><span class="p">(</span><span class="n">BUFSIZ</span><span class="p">);</span><span class="w"> </span><span class="cm">/* for I/O */</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">buf</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nb">NULL</span><span class="p">)</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">PyErr_NoMemory</span><span class="p">();</span>
<span class="p">...</span><span class="n">Do</span><span class="w"> </span><span class="n">some</span><span class="w"> </span><span class="n">I</span><span class="o">/</span><span class="n">O</span><span class="w"> </span><span class="n">operation</span><span class="w"> </span><span class="n">involving</span><span class="w"> </span><span class="n">buf</span><span class="p">...</span>
<span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyBytes_FromString</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span>
<span class="n">free</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span><span class="w"> </span><span class="cm">/* malloc&#39;ed */</span>
<span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
</pre></div>
</div>
<p>In this example, the memory request for the I/O buffer is handled by the C
library allocator. The Python memory manager is involved only in the allocation
of the bytes object returned as a result.</p>
<p>In most situations, however, it is recommended to allocate memory from the
Python heap specifically because the latter is under control of the Python
memory manager. For example, this is required when the interpreter is extended
with new object types written in C. Another reason for using the Python heap is
the desire to <em>inform</em> the Python memory manager about the memory needs of the
extension module. Even when the requested memory is used exclusively for
internal, highly specific purposes, delegating all memory requests to the Python
memory manager causes the interpreter to have a more accurate image of its
memory footprint as a whole. Consequently, under certain circumstances, the
Python memory manager may or may not trigger appropriate actions, like garbage
collection, memory compaction or other preventive procedures. Note that by using
the C library allocator as shown in the previous example, the allocated memory
for the I/O buffer escapes completely the Python memory manager.</p>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p>The <span class="target" id="index-1"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONMALLOC"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONMALLOC</span></code></a> environment variable can be used to configure
the memory allocators used by Python.</p>
<p>The <span class="target" id="index-2"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONMALLOCSTATS"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONMALLOCSTATS</span></code></a> environment variable can be used to print
statistics of the <a class="reference internal" href="#pymalloc"><span class="std std-ref">pymalloc memory allocator</span></a> every time a
new pymalloc object arena is created, and on shutdown.</p>
</div>
</section>
<section id="allocator-domains">
<h2>Allocator Domains<a class="headerlink" href="#allocator-domains" title="Link to this heading"></a></h2>
<p id="id1">All allocating functions belong to one of three different “domains” (see also
<a class="reference internal" href="#c.PyMemAllocatorDomain" title="PyMemAllocatorDomain"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyMemAllocatorDomain</span></code></a>). These domains represent different allocation
strategies and are optimized for different purposes. The specific details on
how every domain allocates memory or what internal functions each domain calls
is considered an implementation detail, but for debugging purposes a simplified
table can be found at <a class="reference internal" href="#default-memory-allocators"><span class="std std-ref">here</span></a>.
The APIs used to allocate and free a block of memory must be from the same domain.
For example, <a class="reference internal" href="#c.PyMem_Free" title="PyMem_Free"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Free()</span></code></a> must be used to free memory allocated using <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>.</p>
<p>The three allocation domains are:</p>
<ul class="simple">
<li><p>Raw domain: intended for allocating memory for general-purpose memory
buffers where the allocation <em>must</em> go to the system allocator or where the
allocator can operate without the <a class="reference internal" href="../glossary.html#term-GIL"><span class="xref std std-term">GIL</span></a>. The memory is requested directly
from the system. See <a class="reference internal" href="#raw-memoryinterface"><span class="std std-ref">Raw Memory Interface</span></a>.</p></li>
<li><p>“Mem” domain: intended for allocating memory for Python buffers and
general-purpose memory buffers where the allocation must be performed with
the <a class="reference internal" href="../glossary.html#term-GIL"><span class="xref std std-term">GIL</span></a> held. The memory is taken from the Python private heap.
See <a class="reference internal" href="#memoryinterface"><span class="std std-ref">Memory Interface</span></a>.</p></li>
<li><p>Object domain: intended for allocating memory for Python objects. The
memory is taken from the Python private heap. See <a class="reference internal" href="#objectinterface"><span class="std std-ref">Object allocators</span></a>.</p></li>
</ul>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <a class="reference internal" href="../glossary.html#term-free-threading"><span class="xref std std-term">free-threaded</span></a> build requires that only Python objects are allocated using the “object” domain
and that all Python objects are allocated using that domain. This differs from the prior Python versions,
where this was only a best practice and not a hard requirement.</p>
<p>For example, buffers (non-Python objects) should be allocated using <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>,
<a class="reference internal" href="#c.PyMem_RawMalloc" title="PyMem_RawMalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawMalloc()</span></code></a>, or <code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code>, but not <a class="reference internal" href="#c.PyObject_Malloc" title="PyObject_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Malloc()</span></code></a>.</p>
<p>See <a class="reference internal" href="../howto/free-threading-extensions.html#free-threaded-memory-allocation"><span class="std std-ref">Memory Allocation APIs</span></a>.</p>
</div>
</section>
<section id="raw-memory-interface">
<span id="raw-memoryinterface"></span><h2>Raw Memory Interface<a class="headerlink" href="#raw-memory-interface" title="Link to this heading"></a></h2>
<p>The following function sets are wrappers to the system allocator. These
functions are thread-safe, the <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">GIL</span></a> does not
need to be held.</p>
<p>The <a class="reference internal" href="#default-memory-allocators"><span class="std std-ref">default raw memory allocator</span></a> uses
the following functions: <code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">calloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">realloc()</span></code>
and <code class="xref c c-func docutils literal notranslate"><span class="pre">free()</span></code>; call <code class="docutils literal notranslate"><span class="pre">malloc(1)</span></code> (or <code class="docutils literal notranslate"><span class="pre">calloc(1,</span> <span class="pre">1)</span></code>) when requesting
zero bytes.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.4.</span></p>
</div>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_RawMalloc">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_RawMalloc</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">n</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_RawMalloc" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.13.</em><p>Allocates <em>n</em> bytes and returns a pointer of type <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span> to the
allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the request fails.</p>
<p>Requesting zero bytes returns a distinct non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as
if <code class="docutils literal notranslate"><span class="pre">PyMem_RawMalloc(1)</span></code> had been called instead. The memory will not have
been initialized in any way.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_RawCalloc">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_RawCalloc</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">nelem</span></span>, <span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">elsize</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_RawCalloc" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.13.</em><p>Allocates <em>nelem</em> elements each whose size in bytes is <em>elsize</em> and returns
a pointer of type <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span> to the allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the
request fails. The memory is initialized to zeros.</p>
<p>Requesting zero elements or elements of size zero bytes returns a distinct
non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as if <code class="docutils literal notranslate"><span class="pre">PyMem_RawCalloc(1,</span> <span class="pre">1)</span></code> had been
called instead.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.5.</span></p>
</div>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_RawRealloc">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_RawRealloc</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">p</span></span>, <span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">n</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_RawRealloc" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.13.</em><p>Resizes the memory block pointed to by <em>p</em> to <em>n</em> bytes. The contents will
be unchanged to the minimum of the old and the new sizes.</p>
<p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the call is equivalent to <code class="docutils literal notranslate"><span class="pre">PyMem_RawMalloc(n)</span></code>; else if
<em>n</em> is equal to zero, the memory block is resized but is not freed, and the
returned pointer is non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
<p>Unless <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, it must have been returned by a previous call to
<a class="reference internal" href="#c.PyMem_RawMalloc" title="PyMem_RawMalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawMalloc()</span></code></a>, <a class="reference internal" href="#c.PyMem_RawRealloc" title="PyMem_RawRealloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawRealloc()</span></code></a> or
<a class="reference internal" href="#c.PyMem_RawCalloc" title="PyMem_RawCalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawCalloc()</span></code></a>.</p>
<p>If the request fails, <a class="reference internal" href="#c.PyMem_RawRealloc" title="PyMem_RawRealloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawRealloc()</span></code></a> returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> and <em>p</em>
remains a valid pointer to the previous memory area.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_RawFree">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_RawFree</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">p</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_RawFree" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.13.</em><p>Frees the memory block pointed to by <em>p</em>, which must have been returned by a
previous call to <a class="reference internal" href="#c.PyMem_RawMalloc" title="PyMem_RawMalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawMalloc()</span></code></a>, <a class="reference internal" href="#c.PyMem_RawRealloc" title="PyMem_RawRealloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawRealloc()</span></code></a> or
<a class="reference internal" href="#c.PyMem_RawCalloc" title="PyMem_RawCalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawCalloc()</span></code></a>. Otherwise, or if <code class="docutils literal notranslate"><span class="pre">PyMem_RawFree(p)</span></code> has been
called before, undefined behavior occurs.</p>
<p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, no operation is performed.</p>
</dd></dl>
</section>
<section id="memory-interface">
<span id="memoryinterface"></span><h2>Memory Interface<a class="headerlink" href="#memory-interface" title="Link to this heading"></a></h2>
<p>The following function sets, modeled after the ANSI C standard, but specifying
behavior when requesting zero bytes, are available for allocating and releasing
memory from the Python heap.</p>
<p>The <a class="reference internal" href="#default-memory-allocators"><span class="std std-ref">default memory allocator</span></a> uses the
<a class="reference internal" href="#pymalloc"><span class="std std-ref">pymalloc memory allocator</span></a>.</p>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>The <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">GIL</span></a> must be held when using these
functions.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.6: </span>The default allocator is now pymalloc instead of system <code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code>.</p>
</div>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_Malloc">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_Malloc</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">n</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Malloc" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Allocates <em>n</em> bytes and returns a pointer of type <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span> to the
allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the request fails.</p>
<p>Requesting zero bytes returns a distinct non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as
if <code class="docutils literal notranslate"><span class="pre">PyMem_Malloc(1)</span></code> had been called instead. The memory will not have
been initialized in any way.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_Calloc">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_Calloc</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">nelem</span></span>, <span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">elsize</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Calloc" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.7.</em><p>Allocates <em>nelem</em> elements each whose size in bytes is <em>elsize</em> and returns
a pointer of type <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span> to the allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the
request fails. The memory is initialized to zeros.</p>
<p>Requesting zero elements or elements of size zero bytes returns a distinct
non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as if <code class="docutils literal notranslate"><span class="pre">PyMem_Calloc(1,</span> <span class="pre">1)</span></code> had been called
instead.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.5.</span></p>
</div>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_Realloc">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_Realloc</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">p</span></span>, <span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">n</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Realloc" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Resizes the memory block pointed to by <em>p</em> to <em>n</em> bytes. The contents will be
unchanged to the minimum of the old and the new sizes.</p>
<p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the call is equivalent to <code class="docutils literal notranslate"><span class="pre">PyMem_Malloc(n)</span></code>; else if <em>n</em>
is equal to zero, the memory block is resized but is not freed, and the
returned pointer is non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
<p>Unless <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, it must have been returned by a previous call to
<a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>, <a class="reference internal" href="#c.PyMem_Realloc" title="PyMem_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Realloc()</span></code></a> or <a class="reference internal" href="#c.PyMem_Calloc" title="PyMem_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Calloc()</span></code></a>.</p>
<p>If the request fails, <a class="reference internal" href="#c.PyMem_Realloc" title="PyMem_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Realloc()</span></code></a> returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> and <em>p</em> remains
a valid pointer to the previous memory area.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_Free">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_Free</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">p</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Free" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Frees the memory block pointed to by <em>p</em>, which must have been returned by a
previous call to <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>, <a class="reference internal" href="#c.PyMem_Realloc" title="PyMem_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Realloc()</span></code></a> or
<a class="reference internal" href="#c.PyMem_Calloc" title="PyMem_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Calloc()</span></code></a>. Otherwise, or if <code class="docutils literal notranslate"><span class="pre">PyMem_Free(p)</span></code> has been called
before, undefined behavior occurs.</p>
<p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, no operation is performed.</p>
</dd></dl>
<p>The following type-oriented macros are provided for convenience. Note that
<em>TYPE</em> refers to any C type.</p>
<dl class="c macro">
<dt class="sig sig-object c" id="c.PyMem_New">
<span class="sig-name descname"><span class="n"><span class="pre">PyMem_New</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">TYPE</span></span>, <span class="n"><span class="pre">n</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_New" title="Link to this definition"></a><br /></dt>
<dd><p>Same as <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>, but allocates <code class="docutils literal notranslate"><span class="pre">(n</span> <span class="pre">*</span> <span class="pre">sizeof(TYPE))</span></code> bytes of
memory. Returns a pointer cast to <code class="docutils literal notranslate"><span class="pre">TYPE*</span></code>. The memory will not have
been initialized in any way.</p>
</dd></dl>
<dl class="c macro">
<dt class="sig sig-object c" id="c.PyMem_Resize">
<span class="sig-name descname"><span class="n"><span class="pre">PyMem_Resize</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">p</span></span>, <span class="n"><span class="pre">TYPE</span></span>, <span class="n"><span class="pre">n</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Resize" title="Link to this definition"></a><br /></dt>
<dd><p>Same as <a class="reference internal" href="#c.PyMem_Realloc" title="PyMem_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Realloc()</span></code></a>, but the memory block is resized to <code class="docutils literal notranslate"><span class="pre">(n</span> <span class="pre">*</span>
<span class="pre">sizeof(TYPE))</span></code> bytes. Returns a pointer cast to <code class="docutils literal notranslate"><span class="pre">TYPE*</span></code>. On return,
<em>p</em> will be a pointer to the new memory area, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> in the event of
failure.</p>
<p>This is a C preprocessor macro; <em>p</em> is always reassigned. Save the original
value of <em>p</em> to avoid losing memory when handling errors.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_Del">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_Del</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">p</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_Del" title="Link to this definition"></a><br /></dt>
<dd><p>Same as <a class="reference internal" href="#c.PyMem_Free" title="PyMem_Free"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Free()</span></code></a>.</p>
</dd></dl>
<p>In addition, the following macro sets are provided for calling the Python memory
allocator directly, without involving the C API functions listed above. However,
note that their use does not preserve binary compatibility across Python
versions and is therefore deprecated in extension modules.</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">PyMem_MALLOC(size)</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">PyMem_NEW(type,</span> <span class="pre">size)</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">PyMem_REALLOC(ptr,</span> <span class="pre">size)</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">PyMem_RESIZE(ptr,</span> <span class="pre">type,</span> <span class="pre">size)</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">PyMem_FREE(ptr)</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">PyMem_DEL(ptr)</span></code></p></li>
</ul>
</section>
<section id="object-allocators">
<span id="objectinterface"></span><h2>Object allocators<a class="headerlink" href="#object-allocators" title="Link to this heading"></a></h2>
<p>The following function sets, modeled after the ANSI C standard, but specifying
behavior when requesting zero bytes, are available for allocating and releasing
memory from the Python heap.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>There is no guarantee that the memory returned by these allocators can be
successfully cast to a Python object when intercepting the allocating
functions in this domain by the methods described in
the <a class="reference internal" href="#customize-memory-allocators"><span class="std std-ref">Customize Memory Allocators</span></a> section.</p>
</div>
<p>The <a class="reference internal" href="#default-memory-allocators"><span class="std std-ref">default object allocator</span></a> uses the
<a class="reference internal" href="#pymalloc"><span class="std std-ref">pymalloc memory allocator</span></a>.</p>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>The <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">GIL</span></a> must be held when using these
functions.</p>
</div>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyObject_Malloc">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyObject_Malloc</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">n</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_Malloc" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Allocates <em>n</em> bytes and returns a pointer of type <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span> to the
allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the request fails.</p>
<p>Requesting zero bytes returns a distinct non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as
if <code class="docutils literal notranslate"><span class="pre">PyObject_Malloc(1)</span></code> had been called instead. The memory will not have
been initialized in any way.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyObject_Calloc">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyObject_Calloc</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">nelem</span></span>, <span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">elsize</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_Calloc" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a> since version 3.7.</em><p>Allocates <em>nelem</em> elements each whose size in bytes is <em>elsize</em> and returns
a pointer of type <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span> to the allocated memory, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the
request fails. The memory is initialized to zeros.</p>
<p>Requesting zero elements or elements of size zero bytes returns a distinct
non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer if possible, as if <code class="docutils literal notranslate"><span class="pre">PyObject_Calloc(1,</span> <span class="pre">1)</span></code> had been called
instead.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.5.</span></p>
</div>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyObject_Realloc">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyObject_Realloc</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">p</span></span>, <span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">n</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_Realloc" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Resizes the memory block pointed to by <em>p</em> to <em>n</em> bytes. The contents will be
unchanged to the minimum of the old and the new sizes.</p>
<p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the call is equivalent to <code class="docutils literal notranslate"><span class="pre">PyObject_Malloc(n)</span></code>; else if <em>n</em>
is equal to zero, the memory block is resized but is not freed, and the
returned pointer is non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
<p>Unless <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, it must have been returned by a previous call to
<a class="reference internal" href="#c.PyObject_Malloc" title="PyObject_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Malloc()</span></code></a>, <a class="reference internal" href="#c.PyObject_Realloc" title="PyObject_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Realloc()</span></code></a> or <a class="reference internal" href="#c.PyObject_Calloc" title="PyObject_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Calloc()</span></code></a>.</p>
<p>If the request fails, <a class="reference internal" href="#c.PyObject_Realloc" title="PyObject_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Realloc()</span></code></a> returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> and <em>p</em> remains
a valid pointer to the previous memory area.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyObject_Free">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyObject_Free</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">p</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_Free" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Frees the memory block pointed to by <em>p</em>, which must have been returned by a
previous call to <a class="reference internal" href="#c.PyObject_Malloc" title="PyObject_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Malloc()</span></code></a>, <a class="reference internal" href="#c.PyObject_Realloc" title="PyObject_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Realloc()</span></code></a> or
<a class="reference internal" href="#c.PyObject_Calloc" title="PyObject_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Calloc()</span></code></a>. Otherwise, or if <code class="docutils literal notranslate"><span class="pre">PyObject_Free(p)</span></code> has been called
before, undefined behavior occurs.</p>
<p>If <em>p</em> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, no operation is performed.</p>
</dd></dl>
</section>
<section id="default-memory-allocators">
<span id="id2"></span><h2>Default Memory Allocators<a class="headerlink" href="#default-memory-allocators" title="Link to this heading"></a></h2>
<p>Default memory allocators:</p>
<table class="docutils align-default">
<thead>
<tr class="row-odd"><th class="head"><p>Configuration</p></th>
<th class="head"><p>Name</p></th>
<th class="head"><p>PyMem_RawMalloc</p></th>
<th class="head"><p>PyMem_Malloc</p></th>
<th class="head"><p>PyObject_Malloc</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p>Release build</p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">&quot;pymalloc&quot;</span></code></p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code></p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">pymalloc</span></code></p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">pymalloc</span></code></p></td>
</tr>
<tr class="row-odd"><td><p>Debug build</p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">&quot;pymalloc_debug&quot;</span></code></p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code> + debug</p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">pymalloc</span></code> + debug</p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">pymalloc</span></code> + debug</p></td>
</tr>
<tr class="row-even"><td><p>Release build, without pymalloc</p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">&quot;malloc&quot;</span></code></p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code></p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code></p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code></p></td>
</tr>
<tr class="row-odd"><td><p>Debug build, without pymalloc</p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">&quot;malloc_debug&quot;</span></code></p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code> + debug</p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code> + debug</p></td>
<td><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code> + debug</p></td>
</tr>
</tbody>
</table>
<p>Legend:</p>
<ul class="simple">
<li><p>Name: value for <span class="target" id="index-3"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONMALLOC"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONMALLOC</span></code></a> environment variable.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">malloc</span></code>: system allocators from the standard C library, C functions:
<code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">calloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">realloc()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">free()</span></code>.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">pymalloc</span></code>: <a class="reference internal" href="#pymalloc"><span class="std std-ref">pymalloc memory allocator</span></a>.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">mimalloc</span></code>: <a class="reference internal" href="#mimalloc"><span class="std std-ref">mimalloc memory allocator</span></a>. The pymalloc
allocator will be used if mimalloc support isn’t available.</p></li>
<li><p>“+ debug”: with <a class="reference internal" href="#pymem-debug-hooks"><span class="std std-ref">debug hooks on the Python memory allocators</span></a>.</p></li>
<li><p>“Debug build”: <a class="reference internal" href="../using/configure.html#debug-build"><span class="std std-ref">Python build in debug mode</span></a>.</p></li>
</ul>
</section>
<section id="customize-memory-allocators">
<span id="id3"></span><h2>Customize Memory Allocators<a class="headerlink" href="#customize-memory-allocators" title="Link to this heading"></a></h2>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.4.</span></p>
</div>
<dl class="c type">
<dt class="sig sig-object c" id="c.PyMemAllocatorEx">
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyMemAllocatorEx</span></span></span><a class="headerlink" href="#c.PyMemAllocatorEx" title="Link to this definition"></a><br /></dt>
<dd><p>Structure used to describe a memory block allocator. The structure has
the following fields:</p>
<table class="docutils align-default">
<thead>
<tr class="row-odd"><th class="head"><p>Field</p></th>
<th class="head"><p>Meaning</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">void</span> <span class="pre">*ctx</span></code></p></td>
<td><p>user context passed as first argument</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">void*</span> <span class="pre">malloc(void</span> <span class="pre">*ctx,</span> <span class="pre">size_t</span> <span class="pre">size)</span></code></p></td>
<td><p>allocate a memory block</p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">void*</span> <span class="pre">calloc(void</span> <span class="pre">*ctx,</span> <span class="pre">size_t</span> <span class="pre">nelem,</span> <span class="pre">size_t</span> <span class="pre">elsize)</span></code></p></td>
<td><p>allocate a memory block initialized
with zeros</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">void*</span> <span class="pre">realloc(void</span> <span class="pre">*ctx,</span> <span class="pre">void</span> <span class="pre">*ptr,</span> <span class="pre">size_t</span> <span class="pre">new_size)</span></code></p></td>
<td><p>allocate or resize a memory block</p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">void</span> <span class="pre">free(void</span> <span class="pre">*ctx,</span> <span class="pre">void</span> <span class="pre">*ptr)</span></code></p></td>
<td><p>free a memory block</p></td>
</tr>
</tbody>
</table>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.5: </span>The <code class="xref c c-type docutils literal notranslate"><span class="pre">PyMemAllocator</span></code> structure was renamed to
<a class="reference internal" href="#c.PyMemAllocatorEx" title="PyMemAllocatorEx"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyMemAllocatorEx</span></code></a> and a new <code class="docutils literal notranslate"><span class="pre">calloc</span></code> field was added.</p>
</div>
</dd></dl>
<dl class="c type">
<dt class="sig sig-object c" id="c.PyMemAllocatorDomain">
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyMemAllocatorDomain</span></span></span><a class="headerlink" href="#c.PyMemAllocatorDomain" title="Link to this definition"></a><br /></dt>
<dd><p>Enum used to identify an allocator domain. Domains:</p>
<dl class="c macro">
<dt class="sig sig-object c" id="c.PYMEM_DOMAIN_RAW">
<span class="sig-name descname"><span class="n"><span class="pre">PYMEM_DOMAIN_RAW</span></span></span><a class="headerlink" href="#c.PYMEM_DOMAIN_RAW" title="Link to this definition"></a><br /></dt>
<dd><p>Functions:</p>
<ul class="simple">
<li><p><a class="reference internal" href="#c.PyMem_RawMalloc" title="PyMem_RawMalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawMalloc()</span></code></a></p></li>
<li><p><a class="reference internal" href="#c.PyMem_RawRealloc" title="PyMem_RawRealloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawRealloc()</span></code></a></p></li>
<li><p><a class="reference internal" href="#c.PyMem_RawCalloc" title="PyMem_RawCalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawCalloc()</span></code></a></p></li>
<li><p><a class="reference internal" href="#c.PyMem_RawFree" title="PyMem_RawFree"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawFree()</span></code></a></p></li>
</ul>
</dd></dl>
<dl class="c macro">
<dt class="sig sig-object c" id="c.PYMEM_DOMAIN_MEM">
<span class="sig-name descname"><span class="n"><span class="pre">PYMEM_DOMAIN_MEM</span></span></span><a class="headerlink" href="#c.PYMEM_DOMAIN_MEM" title="Link to this definition"></a><br /></dt>
<dd><p>Functions:</p>
<ul class="simple">
<li><p><a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>,</p></li>
<li><p><a class="reference internal" href="#c.PyMem_Realloc" title="PyMem_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Realloc()</span></code></a></p></li>
<li><p><a class="reference internal" href="#c.PyMem_Calloc" title="PyMem_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Calloc()</span></code></a></p></li>
<li><p><a class="reference internal" href="#c.PyMem_Free" title="PyMem_Free"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Free()</span></code></a></p></li>
</ul>
</dd></dl>
<dl class="c macro">
<dt class="sig sig-object c" id="c.PYMEM_DOMAIN_OBJ">
<span class="sig-name descname"><span class="n"><span class="pre">PYMEM_DOMAIN_OBJ</span></span></span><a class="headerlink" href="#c.PYMEM_DOMAIN_OBJ" title="Link to this definition"></a><br /></dt>
<dd><p>Functions:</p>
<ul class="simple">
<li><p><a class="reference internal" href="#c.PyObject_Malloc" title="PyObject_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Malloc()</span></code></a></p></li>
<li><p><a class="reference internal" href="#c.PyObject_Realloc" title="PyObject_Realloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Realloc()</span></code></a></p></li>
<li><p><a class="reference internal" href="#c.PyObject_Calloc" title="PyObject_Calloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Calloc()</span></code></a></p></li>
<li><p><a class="reference internal" href="#c.PyObject_Free" title="PyObject_Free"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Free()</span></code></a></p></li>
</ul>
</dd></dl>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_GetAllocator">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_GetAllocator</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="#c.PyMemAllocatorDomain" title="PyMemAllocatorDomain"><span class="n"><span class="pre">PyMemAllocatorDomain</span></span></a><span class="w"> </span><span class="n"><span class="pre">domain</span></span>, <a class="reference internal" href="#c.PyMemAllocatorEx" title="PyMemAllocatorEx"><span class="n"><span class="pre">PyMemAllocatorEx</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">allocator</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_GetAllocator" title="Link to this definition"></a><br /></dt>
<dd><p>Get the memory block allocator of the specified domain.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_SetAllocator">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_SetAllocator</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="#c.PyMemAllocatorDomain" title="PyMemAllocatorDomain"><span class="n"><span class="pre">PyMemAllocatorDomain</span></span></a><span class="w"> </span><span class="n"><span class="pre">domain</span></span>, <a class="reference internal" href="#c.PyMemAllocatorEx" title="PyMemAllocatorEx"><span class="n"><span class="pre">PyMemAllocatorEx</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">allocator</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_SetAllocator" title="Link to this definition"></a><br /></dt>
<dd><p>Set the memory block allocator of the specified domain.</p>
<p>The new allocator must return a distinct non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer when requesting
zero bytes.</p>
<p>For the <a class="reference internal" href="#c.PYMEM_DOMAIN_RAW" title="PYMEM_DOMAIN_RAW"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_RAW</span></code></a> domain, the allocator must be
thread-safe: the <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">GIL</span></a> is not held when the
allocator is called.</p>
<p>For the remaining domains, the allocator must also be thread-safe:
the allocator may be called in different interpreters that do not
share a <code class="docutils literal notranslate"><span class="pre">GIL</span></code>.</p>
<p>If the new allocator is not a hook (does not call the previous allocator),
the <a class="reference internal" href="#c.PyMem_SetupDebugHooks" title="PyMem_SetupDebugHooks"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_SetupDebugHooks()</span></code></a> function must be called to reinstall the
debug hooks on top on the new allocator.</p>
<p>See also <a class="reference internal" href="init_config.html#c.PyPreConfig.allocator" title="PyPreConfig.allocator"><code class="xref c c-member docutils literal notranslate"><span class="pre">PyPreConfig.allocator</span></code></a> and <a class="reference internal" href="init_config.html#c-preinit"><span class="std std-ref">Preinitialize Python
with PyPreConfig</span></a>.</p>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p><a class="reference internal" href="#c.PyMem_SetAllocator" title="PyMem_SetAllocator"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_SetAllocator()</span></code></a> does have the following contract:</p>
<ul class="simple">
<li><p>It can be called after <a class="reference internal" href="init_config.html#c.Py_PreInitialize" title="Py_PreInitialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_PreInitialize()</span></code></a> and before
<a class="reference internal" href="init.html#c.Py_InitializeFromConfig" title="Py_InitializeFromConfig"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_InitializeFromConfig()</span></code></a> to install a custom memory
allocator. There are no restrictions over the installed allocator
other than the ones imposed by the domain (for instance, the Raw
Domain allows the allocator to be called without the GIL held). See
<a class="reference internal" href="#id1"><span class="std std-ref">the section on allocator domains</span></a> for more
information.</p></li>
<li><p>If called after Python has finish initializing (after
<a class="reference internal" href="init.html#c.Py_InitializeFromConfig" title="Py_InitializeFromConfig"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_InitializeFromConfig()</span></code></a> has been called) the allocator
<strong>must</strong> wrap the existing allocator. Substituting the current
allocator for some other arbitrary one is <strong>not supported</strong>.</p></li>
</ul>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.12: </span>All allocators must be thread-safe.</p>
</div>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyMem_SetupDebugHooks">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyMem_SetupDebugHooks</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMem_SetupDebugHooks" title="Link to this definition"></a><br /></dt>
<dd><p>Setup <a class="reference internal" href="#pymem-debug-hooks"><span class="std std-ref">debug hooks in the Python memory allocators</span></a>
to detect memory errors.</p>
</dd></dl>
</section>
<section id="debug-hooks-on-the-python-memory-allocators">
<span id="pymem-debug-hooks"></span><h2>Debug hooks on the Python memory allocators<a class="headerlink" href="#debug-hooks-on-the-python-memory-allocators" title="Link to this heading"></a></h2>
<p>When <a class="reference internal" href="../using/configure.html#debug-build"><span class="std std-ref">Python is built in debug mode</span></a>, the
<a class="reference internal" href="#c.PyMem_SetupDebugHooks" title="PyMem_SetupDebugHooks"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_SetupDebugHooks()</span></code></a> function is called at the <a class="reference internal" href="init_config.html#c-preinit"><span class="std std-ref">Python
preinitialization</span></a> to setup debug hooks on Python memory allocators
to detect memory errors.</p>
<p>The <span class="target" id="index-4"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONMALLOC"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONMALLOC</span></code></a> environment variable can be used to install debug
hooks on a Python compiled in release mode (ex: <code class="docutils literal notranslate"><span class="pre">PYTHONMALLOC=debug</span></code>).</p>
<p>The <a class="reference internal" href="#c.PyMem_SetupDebugHooks" title="PyMem_SetupDebugHooks"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_SetupDebugHooks()</span></code></a> function can be used to set debug hooks
after calling <a class="reference internal" href="#c.PyMem_SetAllocator" title="PyMem_SetAllocator"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_SetAllocator()</span></code></a>.</p>
<p>These debug hooks fill dynamically allocated memory blocks with special,
recognizable bit patterns. Newly allocated memory is filled with the byte
<code class="docutils literal notranslate"><span class="pre">0xCD</span></code> (<code class="docutils literal notranslate"><span class="pre">PYMEM_CLEANBYTE</span></code>), freed memory is filled with the byte <code class="docutils literal notranslate"><span class="pre">0xDD</span></code>
(<code class="docutils literal notranslate"><span class="pre">PYMEM_DEADBYTE</span></code>). Memory blocks are surrounded by “forbidden bytes”
filled with the byte <code class="docutils literal notranslate"><span class="pre">0xFD</span></code> (<code class="docutils literal notranslate"><span class="pre">PYMEM_FORBIDDENBYTE</span></code>). Strings of these bytes
are unlikely to be valid addresses, floats, or ASCII strings.</p>
<p>Runtime checks:</p>
<ul class="simple">
<li><p>Detect API violations. For example, detect if <a class="reference internal" href="#c.PyObject_Free" title="PyObject_Free"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Free()</span></code></a> is
called on a memory block allocated by <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>.</p></li>
<li><p>Detect write before the start of the buffer (buffer underflow).</p></li>
<li><p>Detect write after the end of the buffer (buffer overflow).</p></li>
<li><p>Check that the <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">GIL</span></a> is held when
allocator functions of <a class="reference internal" href="#c.PYMEM_DOMAIN_OBJ" title="PYMEM_DOMAIN_OBJ"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_OBJ</span></code></a> (ex:
<a class="reference internal" href="#c.PyObject_Malloc" title="PyObject_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Malloc()</span></code></a>) and <a class="reference internal" href="#c.PYMEM_DOMAIN_MEM" title="PYMEM_DOMAIN_MEM"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_MEM</span></code></a> (ex:
<a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>) domains are called.</p></li>
</ul>
<p>On error, the debug hooks use the <a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tracemalloc</span></code></a> module to get the
traceback where a memory block was allocated. The traceback is only displayed
if <a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tracemalloc</span></code></a> is tracing Python memory allocations and the memory block
was traced.</p>
<p>Let <em>S</em> = <code class="docutils literal notranslate"><span class="pre">sizeof(size_t)</span></code>. <code class="docutils literal notranslate"><span class="pre">2*S</span></code> bytes are added at each end of each block
of <em>N</em> bytes requested. The memory layout is like so, where p represents the
address returned by a malloc-like or realloc-like function (<code class="docutils literal notranslate"><span class="pre">p[i:j]</span></code> means
the slice of bytes from <code class="docutils literal notranslate"><span class="pre">*(p+i)</span></code> inclusive up to <code class="docutils literal notranslate"><span class="pre">*(p+j)</span></code> exclusive; note
that the treatment of negative indices differs from a Python slice):</p>
<dl>
<dt><code class="docutils literal notranslate"><span class="pre">p[-2*S:-S]</span></code></dt><dd><p>Number of bytes originally asked for. This is a size_t, big-endian (easier
to read in a memory dump).</p>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">p[-S]</span></code></dt><dd><p>API identifier (ASCII character):</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">'r'</span></code> for <a class="reference internal" href="#c.PYMEM_DOMAIN_RAW" title="PYMEM_DOMAIN_RAW"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_RAW</span></code></a>.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">'m'</span></code> for <a class="reference internal" href="#c.PYMEM_DOMAIN_MEM" title="PYMEM_DOMAIN_MEM"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_MEM</span></code></a>.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">'o'</span></code> for <a class="reference internal" href="#c.PYMEM_DOMAIN_OBJ" title="PYMEM_DOMAIN_OBJ"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_OBJ</span></code></a>.</p></li>
</ul>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">p[-S+1:0]</span></code></dt><dd><p>Copies of PYMEM_FORBIDDENBYTE. Used to catch under- writes and reads.</p>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">p[0:N]</span></code></dt><dd><p>The requested memory, filled with copies of PYMEM_CLEANBYTE, used to catch
reference to uninitialized memory. When a realloc-like function is called
requesting a larger memory block, the new excess bytes are also filled with
PYMEM_CLEANBYTE. When a free-like function is called, these are
overwritten with PYMEM_DEADBYTE, to catch reference to freed memory. When
a realloc- like function is called requesting a smaller memory block, the
excess old bytes are also filled with PYMEM_DEADBYTE.</p>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">p[N:N+S]</span></code></dt><dd><p>Copies of PYMEM_FORBIDDENBYTE. Used to catch over- writes and reads.</p>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">p[N+S:N+2*S]</span></code></dt><dd><p>Only used if the <code class="docutils literal notranslate"><span class="pre">PYMEM_DEBUG_SERIALNO</span></code> macro is defined (not defined by
default).</p>
<p>A serial number, incremented by 1 on each call to a malloc-like or
realloc-like function. Big-endian <code class="xref c c-type docutils literal notranslate"><span class="pre">size_t</span></code>. If “bad memory” is detected
later, the serial number gives an excellent way to set a breakpoint on the
next run, to capture the instant at which this block was passed out. The
static function bumpserialno() in obmalloc.c is the only place the serial
number is incremented, and exists so you can set such a breakpoint easily.</p>
</dd>
</dl>
<p>A realloc-like or free-like function first checks that the PYMEM_FORBIDDENBYTE
bytes at each end are intact. If they’ve been altered, diagnostic output is
written to stderr, and the program is aborted via Py_FatalError(). The other
main failure mode is provoking a memory error when a program reads up one of
the special bit patterns and tries to use it as an address. If you get in a
debugger then and look at the object, you’re likely to see that it’s entirely
filled with PYMEM_DEADBYTE (meaning freed memory is getting used) or
PYMEM_CLEANBYTE (meaning uninitialized memory is getting used).</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.6: </span>The <a class="reference internal" href="#c.PyMem_SetupDebugHooks" title="PyMem_SetupDebugHooks"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_SetupDebugHooks()</span></code></a> function now also works on Python
compiled in release mode. On error, the debug hooks now use
<a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tracemalloc</span></code></a> to get the traceback where a memory block was allocated.
The debug hooks now also check if the GIL is held when functions of
<a class="reference internal" href="#c.PYMEM_DOMAIN_OBJ" title="PYMEM_DOMAIN_OBJ"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_OBJ</span></code></a> and <a class="reference internal" href="#c.PYMEM_DOMAIN_MEM" title="PYMEM_DOMAIN_MEM"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_MEM</span></code></a> domains are
called.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span>Byte patterns <code class="docutils literal notranslate"><span class="pre">0xCB</span></code> (<code class="docutils literal notranslate"><span class="pre">PYMEM_CLEANBYTE</span></code>), <code class="docutils literal notranslate"><span class="pre">0xDB</span></code> (<code class="docutils literal notranslate"><span class="pre">PYMEM_DEADBYTE</span></code>)
and <code class="docutils literal notranslate"><span class="pre">0xFB</span></code> (<code class="docutils literal notranslate"><span class="pre">PYMEM_FORBIDDENBYTE</span></code>) have been replaced with <code class="docutils literal notranslate"><span class="pre">0xCD</span></code>,
<code class="docutils literal notranslate"><span class="pre">0xDD</span></code> and <code class="docutils literal notranslate"><span class="pre">0xFD</span></code> to use the same values than Windows CRT debug
<code class="docutils literal notranslate"><span class="pre">malloc()</span></code> and <code class="docutils literal notranslate"><span class="pre">free()</span></code>.</p>
</div>
</section>
<section id="the-pymalloc-allocator">
<span id="pymalloc"></span><h2>The pymalloc allocator<a class="headerlink" href="#the-pymalloc-allocator" title="Link to this heading"></a></h2>
<p>Python has a <em>pymalloc</em> allocator optimized for small objects (smaller or equal
to 512 bytes) with a short lifetime. It uses memory mappings called “arenas”
with a fixed size of either 256 KiB on 32-bit platforms or 1 MiB on 64-bit
platforms. It falls back to <a class="reference internal" href="#c.PyMem_RawMalloc" title="PyMem_RawMalloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawMalloc()</span></code></a> and
<a class="reference internal" href="#c.PyMem_RawRealloc" title="PyMem_RawRealloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_RawRealloc()</span></code></a> for allocations larger than 512 bytes.</p>
<p><em>pymalloc</em> is the <a class="reference internal" href="#default-memory-allocators"><span class="std std-ref">default allocator</span></a> of the
<a class="reference internal" href="#c.PYMEM_DOMAIN_MEM" title="PYMEM_DOMAIN_MEM"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_MEM</span></code></a> (ex: <a class="reference internal" href="#c.PyMem_Malloc" title="PyMem_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Malloc()</span></code></a>) and
<a class="reference internal" href="#c.PYMEM_DOMAIN_OBJ" title="PYMEM_DOMAIN_OBJ"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PYMEM_DOMAIN_OBJ</span></code></a> (ex: <a class="reference internal" href="#c.PyObject_Malloc" title="PyObject_Malloc"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Malloc()</span></code></a>) domains.</p>
<p>The arena allocator uses the following functions:</p>
<ul class="simple">
<li><p><code class="xref c c-func docutils literal notranslate"><span class="pre">VirtualAlloc()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">VirtualFree()</span></code> on Windows,</p></li>
<li><p><code class="xref c c-func docutils literal notranslate"><span class="pre">mmap()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">munmap()</span></code> if available,</p></li>
<li><p><code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">free()</span></code> otherwise.</p></li>
</ul>
<p>This allocator is disabled if Python is configured with the
<a class="reference internal" href="../using/configure.html#cmdoption-without-pymalloc"><code class="xref std std-option docutils literal notranslate"><span class="pre">--without-pymalloc</span></code></a> option. It can also be disabled at runtime using
the <span class="target" id="index-5"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONMALLOC"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONMALLOC</span></code></a> environment variable (ex: <code class="docutils literal notranslate"><span class="pre">PYTHONMALLOC=malloc</span></code>).</p>
<section id="customize-pymalloc-arena-allocator">
<h3>Customize pymalloc Arena Allocator<a class="headerlink" href="#customize-pymalloc-arena-allocator" title="Link to this heading"></a></h3>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.4.</span></p>
</div>
<dl class="c type">
<dt class="sig sig-object c" id="c.PyObjectArenaAllocator">
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyObjectArenaAllocator</span></span></span><a class="headerlink" href="#c.PyObjectArenaAllocator" title="Link to this definition"></a><br /></dt>
<dd><p>Structure used to describe an arena allocator. The structure has
three fields:</p>
<table class="docutils align-default">
<thead>
<tr class="row-odd"><th class="head"><p>Field</p></th>
<th class="head"><p>Meaning</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">void</span> <span class="pre">*ctx</span></code></p></td>
<td><p>user context passed as first argument</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">void*</span> <span class="pre">alloc(void</span> <span class="pre">*ctx,</span> <span class="pre">size_t</span> <span class="pre">size)</span></code></p></td>
<td><p>allocate an arena of size bytes</p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">void</span> <span class="pre">free(void</span> <span class="pre">*ctx,</span> <span class="pre">void</span> <span class="pre">*ptr,</span> <span class="pre">size_t</span> <span class="pre">size)</span></code></p></td>
<td><p>free an arena</p></td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyObject_GetArenaAllocator">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyObject_GetArenaAllocator</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="#c.PyObjectArenaAllocator" title="PyObjectArenaAllocator"><span class="n"><span class="pre">PyObjectArenaAllocator</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">allocator</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_GetArenaAllocator" title="Link to this definition"></a><br /></dt>
<dd><p>Get the arena allocator.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyObject_SetArenaAllocator">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyObject_SetArenaAllocator</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="#c.PyObjectArenaAllocator" title="PyObjectArenaAllocator"><span class="n"><span class="pre">PyObjectArenaAllocator</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">allocator</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_SetArenaAllocator" title="Link to this definition"></a><br /></dt>
<dd><p>Set the arena allocator.</p>
</dd></dl>
</section>
</section>
<section id="the-mimalloc-allocator">
<span id="mimalloc"></span><h2>The mimalloc allocator<a class="headerlink" href="#the-mimalloc-allocator" title="Link to this heading"></a></h2>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.13.</span></p>
</div>
<p>Python supports the mimalloc allocator when the underlying platform support is available.
mimalloc “is a general purpose allocator with excellent performance characteristics.
Initially developed by Daan Leijen for the runtime systems of the Koka and Lean languages.”</p>
</section>
<section id="tracemalloc-c-api">
<h2>tracemalloc C API<a class="headerlink" href="#tracemalloc-c-api" title="Link to this heading"></a></h2>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.7.</span></p>
</div>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyTraceMalloc_Track">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyTraceMalloc_Track</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">unsigned</span></span><span class="w"> </span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">domain</span></span>, <span class="n"><span class="pre">uintptr_t</span></span><span class="w"> </span><span class="n"><span class="pre">ptr</span></span>, <span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">size</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyTraceMalloc_Track" title="Link to this definition"></a><br /></dt>
<dd><p>Track an allocated memory block in the <a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tracemalloc</span></code></a> module.</p>
<p>Return <code class="docutils literal notranslate"><span class="pre">0</span></code> on success, return <code class="docutils literal notranslate"><span class="pre">-1</span></code> on error (failed to allocate memory to
store the trace). Return <code class="docutils literal notranslate"><span class="pre">-2</span></code> if tracemalloc is disabled.</p>
<p>If memory block is already tracked, update the existing trace.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyTraceMalloc_Untrack">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyTraceMalloc_Untrack</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">unsigned</span></span><span class="w"> </span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">domain</span></span>, <span class="n"><span class="pre">uintptr_t</span></span><span class="w"> </span><span class="n"><span class="pre">ptr</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyTraceMalloc_Untrack" title="Link to this definition"></a><br /></dt>
<dd><p>Untrack an allocated memory block in the <a class="reference internal" href="../library/tracemalloc.html#module-tracemalloc" title="tracemalloc: Trace memory allocations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tracemalloc</span></code></a> module.
Do nothing if the block was not tracked.</p>
<p>Return <code class="docutils literal notranslate"><span class="pre">-2</span></code> if tracemalloc is disabled, otherwise return <code class="docutils literal notranslate"><span class="pre">0</span></code>.</p>
</dd></dl>
</section>
<section id="examples">
<span id="memoryexamples"></span><h2>Examples<a class="headerlink" href="#examples" title="Link to this heading"></a></h2>
<p>Here is the example from section <a class="reference internal" href="#memoryoverview"><span class="std std-ref">Overview</span></a>, rewritten so that the
I/O buffer is allocated from the Python heap by using the first function set:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyObject</span><span class="w"> </span><span class="o">*</span><span class="n">res</span><span class="p">;</span>
<span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="w"> </span><span class="n">PyMem_Malloc</span><span class="p">(</span><span class="n">BUFSIZ</span><span class="p">);</span><span class="w"> </span><span class="cm">/* for I/O */</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">buf</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nb">NULL</span><span class="p">)</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">PyErr_NoMemory</span><span class="p">();</span>
<span class="cm">/* ...Do some I/O operation involving buf... */</span>
<span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyBytes_FromString</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span>
<span class="n">PyMem_Free</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span><span class="w"> </span><span class="cm">/* allocated with PyMem_Malloc */</span>
<span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
</pre></div>
</div>
<p>The same code using the type-oriented function set:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyObject</span><span class="w"> </span><span class="o">*</span><span class="n">res</span><span class="p">;</span>
<span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyMem_New</span><span class="p">(</span><span class="kt">char</span><span class="p">,</span><span class="w"> </span><span class="n">BUFSIZ</span><span class="p">);</span><span class="w"> </span><span class="cm">/* for I/O */</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">buf</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nb">NULL</span><span class="p">)</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">PyErr_NoMemory</span><span class="p">();</span>
<span class="cm">/* ...Do some I/O operation involving buf... */</span>
<span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyBytes_FromString</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span>
<span class="n">PyMem_Del</span><span class="p">(</span><span class="n">buf</span><span class="p">);</span><span class="w"> </span><span class="cm">/* allocated with PyMem_New */</span>
<span class="k">return</span><span class="w"> </span><span class="n">res</span><span class="p">;</span>
</pre></div>
</div>
<p>Note that in the two examples above, the buffer is always manipulated via
functions belonging to the same set. Indeed, it is required to use the same
memory API family for a given memory block, so that the risk of mixing different
allocators is reduced to a minimum. The following code sequence contains two
errors, one of which is labeled as <em>fatal</em> because it mixes two different
allocators operating on different heaps.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buf1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PyMem_New</span><span class="p">(</span><span class="kt">char</span><span class="p">,</span><span class="w"> </span><span class="n">BUFSIZ</span><span class="p">);</span>
<span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buf2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="w"> </span><span class="n">malloc</span><span class="p">(</span><span class="n">BUFSIZ</span><span class="p">);</span>
<span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buf3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="w"> </span><span class="n">PyMem_Malloc</span><span class="p">(</span><span class="n">BUFSIZ</span><span class="p">);</span>
<span class="p">...</span>
<span class="n">PyMem_Del</span><span class="p">(</span><span class="n">buf3</span><span class="p">);</span><span class="w"> </span><span class="cm">/* Wrong -- should be PyMem_Free() */</span>
<span class="n">free</span><span class="p">(</span><span class="n">buf2</span><span class="p">);</span><span class="w"> </span><span class="cm">/* Right -- allocated via malloc() */</span>
<span class="n">free</span><span class="p">(</span><span class="n">buf1</span><span class="p">);</span><span class="w"> </span><span class="cm">/* Fatal -- should be PyMem_Del() */</span>
</pre></div>
</div>
<p>In addition to the functions aimed at handling raw memory blocks from the Python
heap, objects in Python are allocated and released with <a class="reference internal" href="allocation.html#c.PyObject_New" title="PyObject_New"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyObject_New</span></code></a>,
<a class="reference internal" href="allocation.html#c.PyObject_NewVar" title="PyObject_NewVar"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyObject_NewVar</span></code></a> and <a class="reference internal" href="allocation.html#c.PyObject_Del" title="PyObject_Del"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_Del()</span></code></a>.</p>
<p>These will be explained in the next chapter on defining and implementing new
object types in C.</p>
</section>
</section>
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<div class="sphinxsidebar" role="navigation" aria-label="Main">
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<div>
<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Memory Management</a><ul>
<li><a class="reference internal" href="#overview">Overview</a></li>
<li><a class="reference internal" href="#allocator-domains">Allocator Domains</a></li>
<li><a class="reference internal" href="#raw-memory-interface">Raw Memory Interface</a></li>
<li><a class="reference internal" href="#memory-interface">Memory Interface</a></li>
<li><a class="reference internal" href="#object-allocators">Object allocators</a></li>
<li><a class="reference internal" href="#default-memory-allocators">Default Memory Allocators</a></li>
<li><a class="reference internal" href="#customize-memory-allocators">Customize Memory Allocators</a></li>
<li><a class="reference internal" href="#debug-hooks-on-the-python-memory-allocators">Debug hooks on the Python memory allocators</a></li>
<li><a class="reference internal" href="#the-pymalloc-allocator">The pymalloc allocator</a><ul>
<li><a class="reference internal" href="#customize-pymalloc-arena-allocator">Customize pymalloc Arena Allocator</a></li>
</ul>
</li>
<li><a class="reference internal" href="#the-mimalloc-allocator">The mimalloc allocator</a></li>
<li><a class="reference internal" href="#tracemalloc-c-api">tracemalloc C API</a></li>
<li><a class="reference internal" href="#examples">Examples</a></li>
</ul>
</li>
</ul>
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