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<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">queue</span></code> — A synchronized queue class</a><ul>
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<section id="module-queue">
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<span id="queue-a-synchronized-queue-class"></span><h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">queue</span></code> — A synchronized queue class<a class="headerlink" href="#module-queue" title="Link to this heading">¶</a></h1>
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<p><strong>Source code:</strong> <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/3.13/Lib/queue.py">Lib/queue.py</a></p>
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<hr class="docutils" />
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<p>The <a class="reference internal" href="#module-queue" title="queue: A synchronized queue class."><code class="xref py py-mod docutils literal notranslate"><span class="pre">queue</span></code></a> module implements multi-producer, multi-consumer queues.
|
||
It is especially useful in threaded programming when information must be
|
||
exchanged safely between multiple threads. The <a class="reference internal" href="#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a> class in this
|
||
module implements all the required locking semantics.</p>
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<p>The module implements three types of queue, which differ only in the order in
|
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which the entries are retrieved. In a <abbr title="first-in, first-out">FIFO</abbr>
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||
queue, the first tasks added are the first retrieved. In a
|
||
<abbr title="last-in, first-out">LIFO</abbr> queue, the most recently added entry is
|
||
the first retrieved (operating like a stack). With a priority queue,
|
||
the entries are kept sorted (using the <a class="reference internal" href="heapq.html#module-heapq" title="heapq: Heap queue algorithm (a.k.a. priority queue)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">heapq</span></code></a> module) and the
|
||
lowest valued entry is retrieved first.</p>
|
||
<p>Internally, those three types of queues use locks to temporarily block
|
||
competing threads; however, they are not designed to handle reentrancy
|
||
within a thread.</p>
|
||
<p>In addition, the module implements a “simple”
|
||
<abbr title="first-in, first-out">FIFO</abbr> queue type, <a class="reference internal" href="#queue.SimpleQueue" title="queue.SimpleQueue"><code class="xref py py-class docutils literal notranslate"><span class="pre">SimpleQueue</span></code></a>, whose
|
||
specific implementation provides additional guarantees
|
||
in exchange for the smaller functionality.</p>
|
||
<p>The <a class="reference internal" href="#module-queue" title="queue: A synchronized queue class."><code class="xref py py-mod docutils literal notranslate"><span class="pre">queue</span></code></a> module defines the following classes and exceptions:</p>
|
||
<dl class="py class">
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||
<dt class="sig sig-object py" id="queue.Queue">
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||
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">queue.</span></span><span class="sig-name descname"><span class="pre">Queue</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">maxsize</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Constructor for a <abbr title="first-in, first-out">FIFO</abbr> queue. <em>maxsize</em> is
|
||
an integer that sets the upperbound
|
||
limit on the number of items that can be placed in the queue. Insertion will
|
||
block once this size has been reached, until queue items are consumed. If
|
||
<em>maxsize</em> is less than or equal to zero, the queue size is infinite.</p>
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</dd></dl>
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<dl class="py class">
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<dt class="sig sig-object py" id="queue.LifoQueue">
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<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">queue.</span></span><span class="sig-name descname"><span class="pre">LifoQueue</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">maxsize</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.LifoQueue" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Constructor for a <abbr title="last-in, first-out">LIFO</abbr> queue. <em>maxsize</em> is
|
||
an integer that sets the upperbound
|
||
limit on the number of items that can be placed in the queue. Insertion will
|
||
block once this size has been reached, until queue items are consumed. If
|
||
<em>maxsize</em> is less than or equal to zero, the queue size is infinite.</p>
|
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</dd></dl>
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||
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<dl class="py class">
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<dt class="sig sig-object py" id="queue.PriorityQueue">
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<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">queue.</span></span><span class="sig-name descname"><span class="pre">PriorityQueue</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">maxsize</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.PriorityQueue" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Constructor for a priority queue. <em>maxsize</em> is an integer that sets the upperbound
|
||
limit on the number of items that can be placed in the queue. Insertion will
|
||
block once this size has been reached, until queue items are consumed. If
|
||
<em>maxsize</em> is less than or equal to zero, the queue size is infinite.</p>
|
||
<p>The lowest valued entries are retrieved first (the lowest valued entry is the
|
||
one that would be returned by <code class="docutils literal notranslate"><span class="pre">min(entries)</span></code>). A typical pattern for
|
||
entries is a tuple in the form: <code class="docutils literal notranslate"><span class="pre">(priority_number,</span> <span class="pre">data)</span></code>.</p>
|
||
<p>If the <em>data</em> elements are not comparable, the data can be wrapped in a class
|
||
that ignores the data item and only compares the priority number:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span><span class="w"> </span><span class="nn">dataclasses</span><span class="w"> </span><span class="kn">import</span> <span class="n">dataclass</span><span class="p">,</span> <span class="n">field</span>
|
||
<span class="kn">from</span><span class="w"> </span><span class="nn">typing</span><span class="w"> </span><span class="kn">import</span> <span class="n">Any</span>
|
||
|
||
<span class="nd">@dataclass</span><span class="p">(</span><span class="n">order</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
|
||
<span class="k">class</span><span class="w"> </span><span class="nc">PrioritizedItem</span><span class="p">:</span>
|
||
<span class="n">priority</span><span class="p">:</span> <span class="nb">int</span>
|
||
<span class="n">item</span><span class="p">:</span> <span class="n">Any</span><span class="o">=</span><span class="n">field</span><span class="p">(</span><span class="n">compare</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py class">
|
||
<dt class="sig sig-object py" id="queue.SimpleQueue">
|
||
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">queue.</span></span><span class="sig-name descname"><span class="pre">SimpleQueue</span></span><a class="headerlink" href="#queue.SimpleQueue" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Constructor for an unbounded <abbr title="first-in, first-out">FIFO</abbr> queue.
|
||
Simple queues lack advanced functionality such as task tracking.</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">Added in version 3.7.</span></p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py exception">
|
||
<dt class="sig sig-object py" id="queue.Empty">
|
||
<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">queue.</span></span><span class="sig-name descname"><span class="pre">Empty</span></span><a class="headerlink" href="#queue.Empty" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Exception raised when non-blocking <a class="reference internal" href="#queue.Queue.get" title="queue.Queue.get"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get()</span></code></a> (or
|
||
<a class="reference internal" href="#queue.Queue.get_nowait" title="queue.Queue.get_nowait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get_nowait()</span></code></a>) is called
|
||
on a <a class="reference internal" href="#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a> object which is empty.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py exception">
|
||
<dt class="sig sig-object py" id="queue.Full">
|
||
<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">queue.</span></span><span class="sig-name descname"><span class="pre">Full</span></span><a class="headerlink" href="#queue.Full" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Exception raised when non-blocking <a class="reference internal" href="#queue.Queue.put" title="queue.Queue.put"><code class="xref py py-meth docutils literal notranslate"><span class="pre">put()</span></code></a> (or
|
||
<a class="reference internal" href="#queue.Queue.put_nowait" title="queue.Queue.put_nowait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">put_nowait()</span></code></a>) is called
|
||
on a <a class="reference internal" href="#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a> object which is full.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py exception">
|
||
<dt class="sig sig-object py" id="queue.ShutDown">
|
||
<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">queue.</span></span><span class="sig-name descname"><span class="pre">ShutDown</span></span><a class="headerlink" href="#queue.ShutDown" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Exception raised when <a class="reference internal" href="#queue.Queue.put" title="queue.Queue.put"><code class="xref py py-meth docutils literal notranslate"><span class="pre">put()</span></code></a> or <a class="reference internal" href="#queue.Queue.get" title="queue.Queue.get"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get()</span></code></a> is called on
|
||
a <a class="reference internal" href="#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a> object which has been shut down.</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">Added in version 3.13.</span></p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<section id="queue-objects">
|
||
<span id="queueobjects"></span><h2>Queue Objects<a class="headerlink" href="#queue-objects" title="Link to this heading">¶</a></h2>
|
||
<p>Queue objects (<a class="reference internal" href="#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a>, <a class="reference internal" href="#queue.LifoQueue" title="queue.LifoQueue"><code class="xref py py-class docutils literal notranslate"><span class="pre">LifoQueue</span></code></a>, or <a class="reference internal" href="#queue.PriorityQueue" title="queue.PriorityQueue"><code class="xref py py-class docutils literal notranslate"><span class="pre">PriorityQueue</span></code></a>)
|
||
provide the public methods described below.</p>
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.Queue.qsize">
|
||
<span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">qsize</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.qsize" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Return the approximate size of the queue. Note, qsize() > 0 doesn’t
|
||
guarantee that a subsequent get() will not block, nor will qsize() < maxsize
|
||
guarantee that put() will not block.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.Queue.empty">
|
||
<span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">empty</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.empty" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the queue is empty, <code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise. If empty()
|
||
returns <code class="docutils literal notranslate"><span class="pre">True</span></code> it doesn’t guarantee that a subsequent call to put()
|
||
will not block. Similarly, if empty() returns <code class="docutils literal notranslate"><span class="pre">False</span></code> it doesn’t
|
||
guarantee that a subsequent call to get() will not block.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.Queue.full">
|
||
<span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">full</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.full" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the queue is full, <code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise. If full()
|
||
returns <code class="docutils literal notranslate"><span class="pre">True</span></code> it doesn’t guarantee that a subsequent call to get()
|
||
will not block. Similarly, if full() returns <code class="docutils literal notranslate"><span class="pre">False</span></code> it doesn’t
|
||
guarantee that a subsequent call to put() will not block.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.Queue.put">
|
||
<span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">put</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">item</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">block</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">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.put" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Put <em>item</em> into the queue. If optional args <em>block</em> is true and <em>timeout</em> is
|
||
<code class="docutils literal notranslate"><span class="pre">None</span></code> (the default), block if necessary until a free slot is available. If
|
||
<em>timeout</em> is a positive number, it blocks at most <em>timeout</em> seconds and raises
|
||
the <a class="reference internal" href="#queue.Full" title="queue.Full"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Full</span></code></a> exception if no free slot was available within that time.
|
||
Otherwise (<em>block</em> is false), put an item on the queue if a free slot is
|
||
immediately available, else raise the <a class="reference internal" href="#queue.Full" title="queue.Full"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Full</span></code></a> exception (<em>timeout</em> is
|
||
ignored in that case).</p>
|
||
<p>Raises <a class="reference internal" href="#queue.ShutDown" title="queue.ShutDown"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ShutDown</span></code></a> if the queue has been shut down.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.Queue.put_nowait">
|
||
<span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">put_nowait</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">item</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.put_nowait" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">put(item,</span> <span class="pre">block=False)</span></code>.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.Queue.get">
|
||
<span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">get</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">block</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">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.get" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Remove and return an item from the queue. If optional args <em>block</em> is true and
|
||
<em>timeout</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code> (the default), block if necessary until an item is available.
|
||
If <em>timeout</em> is a positive number, it blocks at most <em>timeout</em> seconds and
|
||
raises the <a class="reference internal" href="#queue.Empty" title="queue.Empty"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Empty</span></code></a> exception if no item was available within that time.
|
||
Otherwise (<em>block</em> is false), return an item if one is immediately available,
|
||
else raise the <a class="reference internal" href="#queue.Empty" title="queue.Empty"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Empty</span></code></a> exception (<em>timeout</em> is ignored in that case).</p>
|
||
<p>Prior to 3.0 on POSIX systems, and for all versions on Windows, if
|
||
<em>block</em> is true and <em>timeout</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code>, this operation goes into
|
||
an uninterruptible wait on an underlying lock. This means that no exceptions
|
||
can occur, and in particular a SIGINT will not trigger a <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>.</p>
|
||
<p>Raises <a class="reference internal" href="#queue.ShutDown" title="queue.ShutDown"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ShutDown</span></code></a> if the queue has been shut down and is empty, or if
|
||
the queue has been shut down immediately.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.Queue.get_nowait">
|
||
<span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">get_nowait</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.get_nowait" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">get(False)</span></code>.</p>
|
||
</dd></dl>
|
||
|
||
<p>Two methods are offered to support tracking whether enqueued tasks have been
|
||
fully processed by daemon consumer threads.</p>
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.Queue.task_done">
|
||
<span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">task_done</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.task_done" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Indicate that a formerly enqueued task is complete. Used by queue consumer
|
||
threads. For each <a class="reference internal" href="#queue.Queue.get" title="queue.Queue.get"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get()</span></code></a> used to fetch a task, a subsequent call to
|
||
<a class="reference internal" href="#queue.Queue.task_done" title="queue.Queue.task_done"><code class="xref py py-meth docutils literal notranslate"><span class="pre">task_done()</span></code></a> tells the queue that the processing on the task is complete.</p>
|
||
<p>If a <a class="reference internal" href="#queue.Queue.join" title="queue.Queue.join"><code class="xref py py-meth docutils literal notranslate"><span class="pre">join()</span></code></a> is currently blocking, it will resume when all items have been
|
||
processed (meaning that a <a class="reference internal" href="#queue.Queue.task_done" title="queue.Queue.task_done"><code class="xref py py-meth docutils literal notranslate"><span class="pre">task_done()</span></code></a> call was received for every item
|
||
that had been <a class="reference internal" href="#queue.Queue.put" title="queue.Queue.put"><code class="xref py py-meth docutils literal notranslate"><span class="pre">put()</span></code></a> into the queue).</p>
|
||
<p><code class="docutils literal notranslate"><span class="pre">shutdown(immediate=True)</span></code> calls <a class="reference internal" href="#queue.Queue.task_done" title="queue.Queue.task_done"><code class="xref py py-meth docutils literal notranslate"><span class="pre">task_done()</span></code></a> for each remaining item
|
||
in the queue.</p>
|
||
<p>Raises 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> if called more times than there were items placed in
|
||
the queue.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.Queue.join">
|
||
<span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">join</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.join" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Blocks until all items in the queue have been gotten and processed.</p>
|
||
<p>The count of unfinished tasks goes up whenever an item is added to the queue.
|
||
The count goes down whenever a consumer thread calls <a class="reference internal" href="#queue.Queue.task_done" title="queue.Queue.task_done"><code class="xref py py-meth docutils literal notranslate"><span class="pre">task_done()</span></code></a> to
|
||
indicate that the item was retrieved and all work on it is complete. When the
|
||
count of unfinished tasks drops to zero, <a class="reference internal" href="#queue.Queue.join" title="queue.Queue.join"><code class="xref py py-meth docutils literal notranslate"><span class="pre">join()</span></code></a> unblocks.</p>
|
||
</dd></dl>
|
||
|
||
<p>Example of how to wait for enqueued tasks to be completed:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">threading</span>
|
||
<span class="kn">import</span><span class="w"> </span><span class="nn">queue</span>
|
||
|
||
<span class="n">q</span> <span class="o">=</span> <span class="n">queue</span><span class="o">.</span><span class="n">Queue</span><span class="p">()</span>
|
||
|
||
<span class="k">def</span><span class="w"> </span><span class="nf">worker</span><span class="p">():</span>
|
||
<span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
|
||
<span class="n">item</span> <span class="o">=</span> <span class="n">q</span><span class="o">.</span><span class="n">get</span><span class="p">()</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'Working on </span><span class="si">{</span><span class="n">item</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'Finished </span><span class="si">{</span><span class="n">item</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span>
|
||
<span class="n">q</span><span class="o">.</span><span class="n">task_done</span><span class="p">()</span>
|
||
|
||
<span class="c1"># Turn-on the worker thread.</span>
|
||
<span class="n">threading</span><span class="o">.</span><span class="n">Thread</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">worker</span><span class="p">,</span> <span class="n">daemon</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
|
||
|
||
<span class="c1"># Send thirty task requests to the worker.</span>
|
||
<span class="k">for</span> <span class="n">item</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">30</span><span class="p">):</span>
|
||
<span class="n">q</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="n">item</span><span class="p">)</span>
|
||
|
||
<span class="c1"># Block until all tasks are done.</span>
|
||
<span class="n">q</span><span class="o">.</span><span class="n">join</span><span class="p">()</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s1">'All work completed'</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<section id="terminating-queues">
|
||
<h3>Terminating queues<a class="headerlink" href="#terminating-queues" title="Link to this heading">¶</a></h3>
|
||
<p><a class="reference internal" href="#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a> objects can be made to prevent further interaction by shutting
|
||
them down.</p>
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.Queue.shutdown">
|
||
<span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">shutdown</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">immediate</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.shutdown" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Shut down the queue, making <a class="reference internal" href="#queue.Queue.get" title="queue.Queue.get"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get()</span></code></a> and <a class="reference internal" href="#queue.Queue.put" title="queue.Queue.put"><code class="xref py py-meth docutils literal notranslate"><span class="pre">put()</span></code></a> raise
|
||
<a class="reference internal" href="#queue.ShutDown" title="queue.ShutDown"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ShutDown</span></code></a>.</p>
|
||
<p>By default, <a class="reference internal" href="#queue.Queue.get" title="queue.Queue.get"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get()</span></code></a> on a shut down queue will only raise once the
|
||
queue is empty. Set <em>immediate</em> to true to make <a class="reference internal" href="#queue.Queue.get" title="queue.Queue.get"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get()</span></code></a> raise
|
||
immediately instead.</p>
|
||
<p>All blocked callers of <a class="reference internal" href="#queue.Queue.put" title="queue.Queue.put"><code class="xref py py-meth docutils literal notranslate"><span class="pre">put()</span></code></a> and <a class="reference internal" href="#queue.Queue.get" title="queue.Queue.get"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get()</span></code></a> will be
|
||
unblocked. If <em>immediate</em> is true, a task will be marked as done for each
|
||
remaining item in the queue, which may unblock callers of
|
||
<a class="reference internal" href="#queue.Queue.join" title="queue.Queue.join"><code class="xref py py-meth docutils literal notranslate"><span class="pre">join()</span></code></a>.</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">Added in version 3.13.</span></p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
</section>
|
||
</section>
|
||
<section id="simplequeue-objects">
|
||
<h2>SimpleQueue Objects<a class="headerlink" href="#simplequeue-objects" title="Link to this heading">¶</a></h2>
|
||
<p><a class="reference internal" href="#queue.SimpleQueue" title="queue.SimpleQueue"><code class="xref py py-class docutils literal notranslate"><span class="pre">SimpleQueue</span></code></a> objects provide the public methods described below.</p>
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.SimpleQueue.qsize">
|
||
<span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">qsize</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.qsize" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Return the approximate size of the queue. Note, qsize() > 0 doesn’t
|
||
guarantee that a subsequent get() will not block.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.SimpleQueue.empty">
|
||
<span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">empty</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.empty" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the queue is empty, <code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise. If empty()
|
||
returns <code class="docutils literal notranslate"><span class="pre">False</span></code> it doesn’t guarantee that a subsequent call to get()
|
||
will not block.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.SimpleQueue.put">
|
||
<span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">put</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">item</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">block</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">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.put" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Put <em>item</em> into the queue. The method never blocks and always succeeds
|
||
(except for potential low-level errors such as failure to allocate memory).
|
||
The optional args <em>block</em> and <em>timeout</em> are ignored and only provided
|
||
for compatibility with <a class="reference internal" href="#queue.Queue.put" title="queue.Queue.put"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Queue.put()</span></code></a>.</p>
|
||
<div class="impl-detail compound">
|
||
<p><strong>CPython implementation detail:</strong> This method has a C implementation which is reentrant. That is, a
|
||
<code class="docutils literal notranslate"><span class="pre">put()</span></code> or <code class="docutils literal notranslate"><span class="pre">get()</span></code> call can be interrupted by another <code class="docutils literal notranslate"><span class="pre">put()</span></code>
|
||
call in the same thread without deadlocking or corrupting internal
|
||
state inside the queue. This makes it appropriate for use in
|
||
destructors such as <code class="docutils literal notranslate"><span class="pre">__del__</span></code> methods or <a class="reference internal" href="weakref.html#module-weakref" title="weakref: Support for weak references and weak dictionaries."><code class="xref py py-mod docutils literal notranslate"><span class="pre">weakref</span></code></a> callbacks.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.SimpleQueue.put_nowait">
|
||
<span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">put_nowait</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">item</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.put_nowait" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">put(item,</span> <span class="pre">block=False)</span></code>, provided for compatibility with
|
||
<a class="reference internal" href="#queue.Queue.put_nowait" title="queue.Queue.put_nowait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Queue.put_nowait()</span></code></a>.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.SimpleQueue.get">
|
||
<span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">get</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">block</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">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.get" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Remove and return an item from the queue. If optional args <em>block</em> is true and
|
||
<em>timeout</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code> (the default), block if necessary until an item is available.
|
||
If <em>timeout</em> is a positive number, it blocks at most <em>timeout</em> seconds and
|
||
raises the <a class="reference internal" href="#queue.Empty" title="queue.Empty"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Empty</span></code></a> exception if no item was available within that time.
|
||
Otherwise (<em>block</em> is false), return an item if one is immediately available,
|
||
else raise the <a class="reference internal" href="#queue.Empty" title="queue.Empty"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Empty</span></code></a> exception (<em>timeout</em> is ignored in that case).</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="queue.SimpleQueue.get_nowait">
|
||
<span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">get_nowait</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.get_nowait" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">get(False)</span></code>.</p>
|
||
</dd></dl>
|
||
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt>Class <a class="reference internal" href="multiprocessing.html#multiprocessing.Queue" title="multiprocessing.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">multiprocessing.Queue</span></code></a></dt><dd><p>A queue class for use in a multi-processing (rather than multi-threading)
|
||
context.</p>
|
||
</dd>
|
||
</dl>
|
||
<p><a class="reference internal" href="collections.html#collections.deque" title="collections.deque"><code class="xref py py-class docutils literal notranslate"><span class="pre">collections.deque</span></code></a> is an alternative implementation of unbounded
|
||
queues with fast atomic <a class="reference internal" href="collections.html#collections.deque.append" title="collections.deque.append"><code class="xref py py-meth docutils literal notranslate"><span class="pre">append()</span></code></a> and
|
||
<a class="reference internal" href="collections.html#collections.deque.popleft" title="collections.deque.popleft"><code class="xref py py-meth docutils literal notranslate"><span class="pre">popleft()</span></code></a> operations that do not require locking
|
||
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|
||
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|
||
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">queue</span></code> — A synchronized queue class</a><ul>
|
||
<li><a class="reference internal" href="#queue-objects">Queue Objects</a><ul>
|
||
<li><a class="reference internal" href="#terminating-queues">Terminating queues</a></li>
|
||
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|
||
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|
||
<li><a class="reference internal" href="#simplequeue-objects">SimpleQueue Objects</a></li>
|
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