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<section id="module-_thread">
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<span id="thread-low-level-threading-api"></span><h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">_thread</span></code> — Low-level threading API<a class="headerlink" href="#module-_thread" title="Link to this heading">¶</a></h1>
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<hr class="docutils" id="index-0" />
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<p>This module provides low-level primitives for working with multiple threads
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(also called <em class="dfn">light-weight processes</em> or <em class="dfn">tasks</em>) — multiple threads of
|
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control sharing their global data space. For synchronization, simple locks
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(also called <em class="dfn">mutexes</em> or <em class="dfn">binary semaphores</em>) are provided.
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The <a class="reference internal" href="threading.html#module-threading" title="threading: Thread-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">threading</span></code></a> module provides an easier to use and higher-level
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threading API built on top of this module.</p>
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<div class="versionchanged" id="index-1">
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<p><span class="versionmodified changed">Changed in version 3.7: </span>This module used to be optional, it is now always available.</p>
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</div>
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<p>This module defines the following constants and functions:</p>
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<dl class="py exception">
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<dt class="sig sig-object py" id="thread.error">
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<em class="property"><span class="k"><span class="pre">exception</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">error</span></span><a class="headerlink" href="#thread.error" title="Link to this definition">¶</a></dt>
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||
<dd><p>Raised on thread-specific errors.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.3: </span>This is now a synonym of the built-in <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a>.</p>
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</div>
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</dd></dl>
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<dl class="py data">
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<dt class="sig sig-object py" id="thread.LockType">
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<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">LockType</span></span><a class="headerlink" href="#thread.LockType" title="Link to this definition">¶</a></dt>
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<dd><p>This is the type of lock objects.</p>
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</dd></dl>
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<dl class="py function">
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<dt class="sig sig-object py" id="thread.start_new_thread">
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<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">start_new_thread</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">function</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">args</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">kwargs</span></span></em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.start_new_thread" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Start a new thread and return its identifier. The thread executes the
|
||
function <em>function</em> with the argument list <em>args</em> (which must be a tuple).
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||
The optional <em>kwargs</em> argument specifies a dictionary of keyword arguments.</p>
|
||
<p>When the function returns, the thread silently exits.</p>
|
||
<p>When the function terminates with an unhandled exception,
|
||
<a class="reference internal" href="sys.html#sys.unraisablehook" title="sys.unraisablehook"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.unraisablehook()</span></code></a> is called to handle the exception. The <em>object</em>
|
||
attribute of the hook argument is <em>function</em>. By default, a stack trace is
|
||
printed and then the thread exits (but other threads continue to run).</p>
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||
<p>When the function raises a <a class="reference internal" href="exceptions.html#SystemExit" title="SystemExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SystemExit</span></code></a> exception, it is silently
|
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ignored.</p>
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||
<p class="audit-hook">Raises an <a class="reference internal" href="sys.html#auditing"><span class="std std-ref">auditing event</span></a> <code class="docutils literal notranslate"><span class="pre">_thread.start_new_thread</span></code> with arguments <code class="docutils literal notranslate"><span class="pre">function</span></code>, <code class="docutils literal notranslate"><span class="pre">args</span></code>, <code class="docutils literal notranslate"><span class="pre">kwargs</span></code>.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.8: </span><a class="reference internal" href="sys.html#sys.unraisablehook" title="sys.unraisablehook"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.unraisablehook()</span></code></a> is now used to handle unhandled exceptions.</p>
|
||
</div>
|
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</dd></dl>
|
||
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="thread.interrupt_main">
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<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">interrupt_main</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">signum</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">signal.SIGINT</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em><span class="sig-paren">)</span><a class="headerlink" href="#thread.interrupt_main" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Simulate the effect of a signal arriving in the main thread.
|
||
A thread can use this function to interrupt the main thread, though
|
||
there is no guarantee that the interruption will happen immediately.</p>
|
||
<p>If given, <em>signum</em> is the number of the signal to simulate.
|
||
If <em>signum</em> is not given, <a class="reference internal" href="signal.html#signal.SIGINT" title="signal.SIGINT"><code class="xref py py-const docutils literal notranslate"><span class="pre">signal.SIGINT</span></code></a> is simulated.</p>
|
||
<p>If the given signal isn’t handled by Python (it was set to
|
||
<a class="reference internal" href="signal.html#signal.SIG_DFL" title="signal.SIG_DFL"><code class="xref py py-const docutils literal notranslate"><span class="pre">signal.SIG_DFL</span></code></a> or <a class="reference internal" href="signal.html#signal.SIG_IGN" title="signal.SIG_IGN"><code class="xref py py-const docutils literal notranslate"><span class="pre">signal.SIG_IGN</span></code></a>), this function does
|
||
nothing.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.10: </span>The <em>signum</em> argument is added to customize the signal number.</p>
|
||
</div>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p>This does not emit the corresponding signal but schedules a call to
|
||
the associated handler (if it exists).
|
||
If you want to truly emit the signal, use <a class="reference internal" href="signal.html#signal.raise_signal" title="signal.raise_signal"><code class="xref py py-func docutils literal notranslate"><span class="pre">signal.raise_signal()</span></code></a>.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="thread.exit">
|
||
<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">exit</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.exit" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Raise the <a class="reference internal" href="exceptions.html#SystemExit" title="SystemExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SystemExit</span></code></a> exception. When not caught, this will cause the
|
||
thread to exit silently.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="thread.allocate_lock">
|
||
<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">allocate_lock</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.allocate_lock" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Return a new lock object. Methods of locks are described below. The lock is
|
||
initially unlocked.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="thread.get_ident">
|
||
<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">get_ident</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.get_ident" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Return the ‘thread identifier’ of the current thread. This is a nonzero
|
||
integer. Its value has no direct meaning; it is intended as a magic cookie to
|
||
be used e.g. to index a dictionary of thread-specific data. Thread identifiers
|
||
may be recycled when a thread exits and another thread is created.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="thread.get_native_id">
|
||
<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">get_native_id</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.get_native_id" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Return the native integral Thread ID of the current thread assigned by the kernel.
|
||
This is a non-negative integer.
|
||
Its value may be used to uniquely identify this particular thread system-wide
|
||
(until the thread terminates, after which the value may be recycled by the OS).</p>
|
||
<div class="availability docutils container">
|
||
<p><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: Windows, FreeBSD, Linux, macOS, OpenBSD, NetBSD, AIX, DragonFlyBSD, GNU/kFreeBSD.</p>
|
||
</div>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">Added in version 3.8.</span></p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.13: </span>Added support for GNU/kFreeBSD.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="thread.stack_size">
|
||
<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">stack_size</span></span><span class="sig-paren">(</span><span class="optional">[</span><em class="sig-param"><span class="n"><span class="pre">size</span></span></em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.stack_size" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Return the thread stack size used when creating new threads. The optional
|
||
<em>size</em> argument specifies the stack size to be used for subsequently created
|
||
threads, and must be 0 (use platform or configured default) or a positive
|
||
integer value of at least 32,768 (32 KiB). If <em>size</em> is not specified,
|
||
0 is used. If changing the thread stack size is
|
||
unsupported, a <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a> is raised. If the specified stack size is
|
||
invalid, a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> is raised and the stack size is unmodified. 32 KiB
|
||
is currently the minimum supported stack size value to guarantee sufficient
|
||
stack space for the interpreter itself. Note that some platforms may have
|
||
particular restrictions on values for the stack size, such as requiring a
|
||
minimum stack size > 32 KiB or requiring allocation in multiples of the system
|
||
memory page size - platform documentation should be referred to for more
|
||
information (4 KiB pages are common; using multiples of 4096 for the stack size is
|
||
the suggested approach in the absence of more specific information).</p>
|
||
<div class="availability docutils container">
|
||
<p><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: Windows, pthreads.</p>
|
||
<p>Unix platforms with POSIX threads support.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py data">
|
||
<dt class="sig sig-object py" id="thread.TIMEOUT_MAX">
|
||
<span class="sig-prename descclassname"><span class="pre">_thread.</span></span><span class="sig-name descname"><span class="pre">TIMEOUT_MAX</span></span><a class="headerlink" href="#thread.TIMEOUT_MAX" title="Link to this definition">¶</a></dt>
|
||
<dd><p>The maximum value allowed for the <em>timeout</em> parameter of
|
||
<a class="reference internal" href="threading.html#threading.Lock.acquire" title="threading.Lock.acquire"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Lock.acquire</span></code></a>. Specifying a timeout greater
|
||
than this value will raise an <a class="reference internal" href="exceptions.html#OverflowError" title="OverflowError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OverflowError</span></code></a>.</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">Added in version 3.2.</span></p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<p>Lock objects have the following methods:</p>
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="thread.lock.acquire">
|
||
<span class="sig-prename descclassname"><span class="pre">lock.</span></span><span class="sig-name descname"><span class="pre">acquire</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">blocking</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">-1</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#thread.lock.acquire" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Without any optional argument, this method acquires the lock unconditionally, if
|
||
necessary waiting until it is released by another thread (only one thread at a
|
||
time can acquire a lock — that’s their reason for existence).</p>
|
||
<p>If the <em>blocking</em> argument is present, the action depends on its
|
||
value: if it is false, the lock is only acquired if it can be acquired
|
||
immediately without waiting, while if it is true, the lock is acquired
|
||
unconditionally as above.</p>
|
||
<p>If the floating-point <em>timeout</em> argument is present and positive, it
|
||
specifies the maximum wait time in seconds before returning. A negative
|
||
<em>timeout</em> argument specifies an unbounded wait. You cannot specify
|
||
a <em>timeout</em> if <em>blocking</em> is false.</p>
|
||
<p>The return value is <code class="docutils literal notranslate"><span class="pre">True</span></code> if the lock is acquired successfully,
|
||
<code class="docutils literal notranslate"><span class="pre">False</span></code> if not.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.2: </span>The <em>timeout</em> parameter is new.</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.2: </span>Lock acquires can now be interrupted by signals on POSIX.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="thread.lock.release">
|
||
<span class="sig-prename descclassname"><span class="pre">lock.</span></span><span class="sig-name descname"><span class="pre">release</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.lock.release" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Releases the lock. The lock must have been acquired earlier, but not
|
||
necessarily by the same thread.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="thread.lock.locked">
|
||
<span class="sig-prename descclassname"><span class="pre">lock.</span></span><span class="sig-name descname"><span class="pre">locked</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#thread.lock.locked" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Return the status of the lock: <code class="docutils literal notranslate"><span class="pre">True</span></code> if it has been acquired by some thread,
|
||
<code class="docutils literal notranslate"><span class="pre">False</span></code> if not.</p>
|
||
</dd></dl>
|
||
|
||
<p>In addition to these methods, lock objects can also be used via the
|
||
<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a> statement, e.g.:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">_thread</span>
|
||
|
||
<span class="n">a_lock</span> <span class="o">=</span> <span class="n">_thread</span><span class="o">.</span><span class="n">allocate_lock</span><span class="p">()</span>
|
||
|
||
<span class="k">with</span> <span class="n">a_lock</span><span class="p">:</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s2">"a_lock is locked while this executes"</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p><strong>Caveats:</strong></p>
|
||
<ul class="simple" id="index-2">
|
||
<li><p>Interrupts always go to the main thread (the <a class="reference internal" href="exceptions.html#KeyboardInterrupt" title="KeyboardInterrupt"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyboardInterrupt</span></code></a>
|
||
exception will be received by that thread.)</p></li>
|
||
<li><p>Calling <a class="reference internal" href="sys.html#sys.exit" title="sys.exit"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.exit()</span></code></a> or raising the <a class="reference internal" href="exceptions.html#SystemExit" title="SystemExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SystemExit</span></code></a> exception is
|
||
equivalent to calling <a class="reference internal" href="#thread.exit" title="_thread.exit"><code class="xref py py-func docutils literal notranslate"><span class="pre">_thread.exit()</span></code></a>.</p></li>
|
||
<li><p>It is platform-dependent whether the <a class="reference internal" href="threading.html#threading.Lock.acquire" title="threading.Lock.acquire"><code class="xref py py-meth docutils literal notranslate"><span class="pre">acquire()</span></code></a> method
|
||
on a lock can be interrupted (so that the <a class="reference internal" href="exceptions.html#KeyboardInterrupt" title="KeyboardInterrupt"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyboardInterrupt</span></code></a> exception
|
||
will happen immediately, rather than only after the lock has been acquired or
|
||
the operation has timed out). It can be interrupted on POSIX, but not on
|
||
Windows.</p></li>
|
||
<li><p>When the main thread exits, it is system defined whether the other threads
|
||
survive. On most systems, they are killed without executing
|
||
<a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> … <a class="reference internal" href="../reference/compound_stmts.html#finally"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">finally</span></code></a> clauses or executing object
|
||
destructors.</p></li>
|
||
</ul>
|
||
</section>
|
||
|
||
|
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