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<section id="synchronization-primitives">
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<span id="asyncio-sync"></span><h1>Synchronization Primitives<a class="headerlink" href="#synchronization-primitives" 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/asyncio/locks.py">Lib/asyncio/locks.py</a></p>
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<hr class="docutils" />
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<p>asyncio synchronization primitives are designed to be similar to
|
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those of 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 with two important caveats:</p>
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<ul class="simple">
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<li><p>asyncio primitives are not thread-safe, therefore they should not
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be used for OS thread synchronization (use <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> for
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that);</p></li>
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<li><p>methods of these synchronization primitives do not accept the <em>timeout</em>
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argument; use the <a class="reference internal" href="asyncio-task.html#asyncio.wait_for" title="asyncio.wait_for"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.wait_for()</span></code></a> function to perform
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operations with timeouts.</p></li>
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</ul>
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<p>asyncio has the following basic synchronization primitives:</p>
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<ul class="simple">
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<li><p><a class="reference internal" href="#asyncio.Lock" title="asyncio.Lock"><code class="xref py py-class docutils literal notranslate"><span class="pre">Lock</span></code></a></p></li>
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<li><p><a class="reference internal" href="#asyncio.Event" title="asyncio.Event"><code class="xref py py-class docutils literal notranslate"><span class="pre">Event</span></code></a></p></li>
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<li><p><a class="reference internal" href="#asyncio.Condition" title="asyncio.Condition"><code class="xref py py-class docutils literal notranslate"><span class="pre">Condition</span></code></a></p></li>
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<li><p><a class="reference internal" href="#asyncio.Semaphore" title="asyncio.Semaphore"><code class="xref py py-class docutils literal notranslate"><span class="pre">Semaphore</span></code></a></p></li>
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<li><p><a class="reference internal" href="#asyncio.BoundedSemaphore" title="asyncio.BoundedSemaphore"><code class="xref py py-class docutils literal notranslate"><span class="pre">BoundedSemaphore</span></code></a></p></li>
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<li><p><a class="reference internal" href="#asyncio.Barrier" title="asyncio.Barrier"><code class="xref py py-class docutils literal notranslate"><span class="pre">Barrier</span></code></a></p></li>
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</ul>
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<hr class="docutils" />
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<section id="lock">
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<h2>Lock<a class="headerlink" href="#lock" title="Link to this heading">¶</a></h2>
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<dl class="py class">
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<dt class="sig sig-object py" id="asyncio.Lock">
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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">asyncio.</span></span><span class="sig-name descname"><span class="pre">Lock</span></span><a class="headerlink" href="#asyncio.Lock" title="Link to this definition">¶</a></dt>
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<dd><p>Implements a mutex lock for asyncio tasks. Not thread-safe.</p>
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<p>An asyncio lock can be used to guarantee exclusive access to a
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shared resource.</p>
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<p>The preferred way to use a Lock is an <a class="reference internal" href="../reference/compound_stmts.html#async-with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">with</span></code></a>
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statement:</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">lock</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">Lock</span><span class="p">()</span>
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<span class="c1"># ... later</span>
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<span class="k">async</span> <span class="k">with</span> <span class="n">lock</span><span class="p">:</span>
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<span class="c1"># access shared state</span>
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</pre></div>
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</div>
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<p>which is equivalent to:</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">lock</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">Lock</span><span class="p">()</span>
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<span class="c1"># ... later</span>
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<span class="k">await</span> <span class="n">lock</span><span class="o">.</span><span class="n">acquire</span><span class="p">()</span>
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<span class="k">try</span><span class="p">:</span>
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<span class="c1"># access shared state</span>
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<span class="k">finally</span><span class="p">:</span>
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<span class="n">lock</span><span class="o">.</span><span class="n">release</span><span class="p">()</span>
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</pre></div>
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</div>
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<div class="versionchanged">
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<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>
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</div>
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<dl class="py method">
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<dt class="sig sig-object py" id="asyncio.Lock.acquire">
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<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">acquire</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Lock.acquire" title="Link to this definition">¶</a></dt>
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<dd><p>Acquire the lock.</p>
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<p>This method waits until the lock is <em>unlocked</em>, sets it to
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<em>locked</em> and returns <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>
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<p>When more than one coroutine is blocked in <a class="reference internal" href="#asyncio.Lock.acquire" title="asyncio.Lock.acquire"><code class="xref py py-meth docutils literal notranslate"><span class="pre">acquire()</span></code></a>
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waiting for the lock to be unlocked, only one coroutine
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eventually proceeds.</p>
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<p>Acquiring a lock is <em>fair</em>: the coroutine that proceeds will be
|
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the first coroutine that started waiting on the lock.</p>
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</dd></dl>
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<dl class="py method">
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<dt class="sig sig-object py" id="asyncio.Lock.release">
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<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="#asyncio.Lock.release" title="Link to this definition">¶</a></dt>
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<dd><p>Release the lock.</p>
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<p>When the lock is <em>locked</em>, reset it to <em>unlocked</em> and return.</p>
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<p>If the lock is <em>unlocked</em>, 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.</p>
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</dd></dl>
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|
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<dl class="py method">
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<dt class="sig sig-object py" id="asyncio.Lock.locked">
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<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="#asyncio.Lock.locked" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the lock is <em>locked</em>.</p>
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</dd></dl>
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|
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</dd></dl>
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|
|
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</section>
|
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<section id="event">
|
|
<h2>Event<a class="headerlink" href="#event" title="Link to this heading">¶</a></h2>
|
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<dl class="py class">
|
|
<dt class="sig sig-object py" id="asyncio.Event">
|
|
<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">asyncio.</span></span><span class="sig-name descname"><span class="pre">Event</span></span><a class="headerlink" href="#asyncio.Event" title="Link to this definition">¶</a></dt>
|
|
<dd><p>An event object. Not thread-safe.</p>
|
|
<p>An asyncio event can be used to notify multiple asyncio tasks
|
|
that some event has happened.</p>
|
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<p>An Event object manages an internal flag that can be set to <em>true</em>
|
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with the <a class="reference internal" href="#asyncio.Event.set" title="asyncio.Event.set"><code class="xref py py-meth docutils literal notranslate"><span class="pre">set()</span></code></a> method and reset to <em>false</em> with the
|
|
<a class="reference internal" href="#asyncio.Event.clear" title="asyncio.Event.clear"><code class="xref py py-meth docutils literal notranslate"><span class="pre">clear()</span></code></a> method. The <a class="reference internal" href="#asyncio.Event.wait" title="asyncio.Event.wait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">wait()</span></code></a> method blocks until the
|
|
flag is set to <em>true</em>. The flag is set to <em>false</em> initially.</p>
|
|
<div class="versionchanged">
|
|
<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>
|
|
</div>
|
|
<p id="asyncio-example-sync-event">Example:</p>
|
|
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">waiter</span><span class="p">(</span><span class="n">event</span><span class="p">):</span>
|
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<span class="nb">print</span><span class="p">(</span><span class="s1">'waiting for it ...'</span><span class="p">)</span>
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<span class="k">await</span> <span class="n">event</span><span class="o">.</span><span class="n">wait</span><span class="p">()</span>
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<span class="nb">print</span><span class="p">(</span><span class="s1">'... got it!'</span><span class="p">)</span>
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<span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">main</span><span class="p">():</span>
|
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<span class="c1"># Create an Event object.</span>
|
|
<span class="n">event</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">Event</span><span class="p">()</span>
|
|
|
|
<span class="c1"># Spawn a Task to wait until 'event' is set.</span>
|
|
<span class="n">waiter_task</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span><span class="n">waiter</span><span class="p">(</span><span class="n">event</span><span class="p">))</span>
|
|
|
|
<span class="c1"># Sleep for 1 second and set the event.</span>
|
|
<span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
|
|
<span class="n">event</span><span class="o">.</span><span class="n">set</span><span class="p">()</span>
|
|
|
|
<span class="c1"># Wait until the waiter task is finished.</span>
|
|
<span class="k">await</span> <span class="n">waiter_task</span>
|
|
|
|
<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
|
|
</pre></div>
|
|
</div>
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Event.wait">
|
|
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">wait</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Event.wait" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Wait until the event is set.</p>
|
|
<p>If the event is set, return <code class="docutils literal notranslate"><span class="pre">True</span></code> immediately.
|
|
Otherwise block until another task calls <a class="reference internal" href="#asyncio.Event.set" title="asyncio.Event.set"><code class="xref py py-meth docutils literal notranslate"><span class="pre">set()</span></code></a>.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Event.set">
|
|
<span class="sig-name descname"><span class="pre">set</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Event.set" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Set the event.</p>
|
|
<p>All tasks waiting for event to be set will be immediately
|
|
awakened.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Event.clear">
|
|
<span class="sig-name descname"><span class="pre">clear</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Event.clear" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Clear (unset) the event.</p>
|
|
<p>Tasks awaiting on <a class="reference internal" href="#asyncio.Event.wait" title="asyncio.Event.wait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">wait()</span></code></a> will now block until the
|
|
<a class="reference internal" href="#asyncio.Event.set" title="asyncio.Event.set"><code class="xref py py-meth docutils literal notranslate"><span class="pre">set()</span></code></a> method is called again.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Event.is_set">
|
|
<span class="sig-name descname"><span class="pre">is_set</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Event.is_set" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the event is set.</p>
|
|
</dd></dl>
|
|
|
|
</dd></dl>
|
|
|
|
</section>
|
|
<section id="condition">
|
|
<h2>Condition<a class="headerlink" href="#condition" title="Link to this heading">¶</a></h2>
|
|
<dl class="py class">
|
|
<dt class="sig sig-object py" id="asyncio.Condition">
|
|
<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">asyncio.</span></span><span class="sig-name descname"><span class="pre">Condition</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">lock</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="#asyncio.Condition" title="Link to this definition">¶</a></dt>
|
|
<dd><p>A Condition object. Not thread-safe.</p>
|
|
<p>An asyncio condition primitive can be used by a task to wait for
|
|
some event to happen and then get exclusive access to a shared
|
|
resource.</p>
|
|
<p>In essence, a Condition object combines the functionality
|
|
of an <a class="reference internal" href="#asyncio.Event" title="asyncio.Event"><code class="xref py py-class docutils literal notranslate"><span class="pre">Event</span></code></a> and a <a class="reference internal" href="#asyncio.Lock" title="asyncio.Lock"><code class="xref py py-class docutils literal notranslate"><span class="pre">Lock</span></code></a>. It is possible to have
|
|
multiple Condition objects share one Lock, which allows coordinating
|
|
exclusive access to a shared resource between different tasks
|
|
interested in particular states of that shared resource.</p>
|
|
<p>The optional <em>lock</em> argument must be a <a class="reference internal" href="#asyncio.Lock" title="asyncio.Lock"><code class="xref py py-class docutils literal notranslate"><span class="pre">Lock</span></code></a> object or
|
|
<code class="docutils literal notranslate"><span class="pre">None</span></code>. In the latter case a new Lock object is created
|
|
automatically.</p>
|
|
<div class="versionchanged">
|
|
<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>
|
|
</div>
|
|
<p>The preferred way to use a Condition is an <a class="reference internal" href="../reference/compound_stmts.html#async-with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">with</span></code></a>
|
|
statement:</p>
|
|
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">cond</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">Condition</span><span class="p">()</span>
|
|
|
|
<span class="c1"># ... later</span>
|
|
<span class="k">async</span> <span class="k">with</span> <span class="n">cond</span><span class="p">:</span>
|
|
<span class="k">await</span> <span class="n">cond</span><span class="o">.</span><span class="n">wait</span><span class="p">()</span>
|
|
</pre></div>
|
|
</div>
|
|
<p>which is equivalent to:</p>
|
|
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">cond</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">Condition</span><span class="p">()</span>
|
|
|
|
<span class="c1"># ... later</span>
|
|
<span class="k">await</span> <span class="n">cond</span><span class="o">.</span><span class="n">acquire</span><span class="p">()</span>
|
|
<span class="k">try</span><span class="p">:</span>
|
|
<span class="k">await</span> <span class="n">cond</span><span class="o">.</span><span class="n">wait</span><span class="p">()</span>
|
|
<span class="k">finally</span><span class="p">:</span>
|
|
<span class="n">cond</span><span class="o">.</span><span class="n">release</span><span class="p">()</span>
|
|
</pre></div>
|
|
</div>
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Condition.acquire">
|
|
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">acquire</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Condition.acquire" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Acquire the underlying lock.</p>
|
|
<p>This method waits until the underlying lock is <em>unlocked</em>,
|
|
sets it to <em>locked</em> and returns <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Condition.notify">
|
|
<span class="sig-name descname"><span class="pre">notify</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">n</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="#asyncio.Condition.notify" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Wake up <em>n</em> tasks (1 by default) waiting on this
|
|
condition. If fewer than <em>n</em> tasks are waiting they are all awakened.</p>
|
|
<p>The lock must be acquired before this method is called and
|
|
released shortly after. If called with an <em>unlocked</em> lock
|
|
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> error is raised.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Condition.locked">
|
|
<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="#asyncio.Condition.locked" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the underlying lock is acquired.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Condition.notify_all">
|
|
<span class="sig-name descname"><span class="pre">notify_all</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Condition.notify_all" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Wake up all tasks waiting on this condition.</p>
|
|
<p>This method acts like <a class="reference internal" href="#asyncio.Condition.notify" title="asyncio.Condition.notify"><code class="xref py py-meth docutils literal notranslate"><span class="pre">notify()</span></code></a>, but wakes up all waiting
|
|
tasks.</p>
|
|
<p>The lock must be acquired before this method is called and
|
|
released shortly after. If called with an <em>unlocked</em> lock
|
|
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> error is raised.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Condition.release">
|
|
<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="#asyncio.Condition.release" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Release the underlying lock.</p>
|
|
<p>When invoked on an unlocked lock, 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.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Condition.wait">
|
|
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">wait</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Condition.wait" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Wait until notified.</p>
|
|
<p>If the calling task has not acquired the lock when this method is
|
|
called, 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.</p>
|
|
<p>This method releases the underlying lock, and then blocks until
|
|
it is awakened by a <a class="reference internal" href="#asyncio.Condition.notify" title="asyncio.Condition.notify"><code class="xref py py-meth docutils literal notranslate"><span class="pre">notify()</span></code></a> or <a class="reference internal" href="#asyncio.Condition.notify_all" title="asyncio.Condition.notify_all"><code class="xref py py-meth docutils literal notranslate"><span class="pre">notify_all()</span></code></a> call.
|
|
Once awakened, the Condition re-acquires its lock and this method
|
|
returns <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>
|
|
<p>Note that a task <em>may</em> return from this call spuriously,
|
|
which is why the caller should always re-check the state
|
|
and be prepared to <a class="reference internal" href="#asyncio.Condition.wait" title="asyncio.Condition.wait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">wait()</span></code></a> again. For this reason, you may
|
|
prefer to use <a class="reference internal" href="#asyncio.Condition.wait_for" title="asyncio.Condition.wait_for"><code class="xref py py-meth docutils literal notranslate"><span class="pre">wait_for()</span></code></a> instead.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Condition.wait_for">
|
|
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">wait_for</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">predicate</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Condition.wait_for" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Wait until a predicate becomes <em>true</em>.</p>
|
|
<p>The predicate must be a callable which result will be
|
|
interpreted as a boolean value. The method will repeatedly
|
|
<a class="reference internal" href="#asyncio.Condition.wait" title="asyncio.Condition.wait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">wait()</span></code></a> until the predicate evaluates to <em>true</em>. The final value is the
|
|
return value.</p>
|
|
</dd></dl>
|
|
|
|
</dd></dl>
|
|
|
|
</section>
|
|
<section id="semaphore">
|
|
<h2>Semaphore<a class="headerlink" href="#semaphore" title="Link to this heading">¶</a></h2>
|
|
<dl class="py class">
|
|
<dt class="sig sig-object py" id="asyncio.Semaphore">
|
|
<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">asyncio.</span></span><span class="sig-name descname"><span class="pre">Semaphore</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</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="#asyncio.Semaphore" title="Link to this definition">¶</a></dt>
|
|
<dd><p>A Semaphore object. Not thread-safe.</p>
|
|
<p>A semaphore manages an internal counter which is decremented by each
|
|
<a class="reference internal" href="#asyncio.Semaphore.acquire" title="asyncio.Semaphore.acquire"><code class="xref py py-meth docutils literal notranslate"><span class="pre">acquire()</span></code></a> call and incremented by each <a class="reference internal" href="#asyncio.Semaphore.release" title="asyncio.Semaphore.release"><code class="xref py py-meth docutils literal notranslate"><span class="pre">release()</span></code></a> call.
|
|
The counter can never go below zero; when <a class="reference internal" href="#asyncio.Semaphore.acquire" title="asyncio.Semaphore.acquire"><code class="xref py py-meth docutils literal notranslate"><span class="pre">acquire()</span></code></a> finds
|
|
that it is zero, it blocks, waiting until some task calls
|
|
<a class="reference internal" href="#asyncio.Semaphore.release" title="asyncio.Semaphore.release"><code class="xref py py-meth docutils literal notranslate"><span class="pre">release()</span></code></a>.</p>
|
|
<p>The optional <em>value</em> argument gives the initial value for the
|
|
internal counter (<code class="docutils literal notranslate"><span class="pre">1</span></code> by default). If the given value is
|
|
less than <code class="docutils literal notranslate"><span class="pre">0</span></code> 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.</p>
|
|
<div class="versionchanged">
|
|
<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>
|
|
</div>
|
|
<p>The preferred way to use a Semaphore is an <a class="reference internal" href="../reference/compound_stmts.html#async-with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">with</span></code></a>
|
|
statement:</p>
|
|
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">sem</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">Semaphore</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span>
|
|
|
|
<span class="c1"># ... later</span>
|
|
<span class="k">async</span> <span class="k">with</span> <span class="n">sem</span><span class="p">:</span>
|
|
<span class="c1"># work with shared resource</span>
|
|
</pre></div>
|
|
</div>
|
|
<p>which is equivalent to:</p>
|
|
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">sem</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">Semaphore</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span>
|
|
|
|
<span class="c1"># ... later</span>
|
|
<span class="k">await</span> <span class="n">sem</span><span class="o">.</span><span class="n">acquire</span><span class="p">()</span>
|
|
<span class="k">try</span><span class="p">:</span>
|
|
<span class="c1"># work with shared resource</span>
|
|
<span class="k">finally</span><span class="p">:</span>
|
|
<span class="n">sem</span><span class="o">.</span><span class="n">release</span><span class="p">()</span>
|
|
</pre></div>
|
|
</div>
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Semaphore.acquire">
|
|
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">acquire</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Semaphore.acquire" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Acquire a semaphore.</p>
|
|
<p>If the internal counter is greater than zero, decrement
|
|
it by one and return <code class="docutils literal notranslate"><span class="pre">True</span></code> immediately. If it is zero, wait
|
|
until a <a class="reference internal" href="#asyncio.Semaphore.release" title="asyncio.Semaphore.release"><code class="xref py py-meth docutils literal notranslate"><span class="pre">release()</span></code></a> is called and return <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Semaphore.locked">
|
|
<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="#asyncio.Semaphore.locked" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Returns <code class="docutils literal notranslate"><span class="pre">True</span></code> if semaphore can not be acquired immediately.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Semaphore.release">
|
|
<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="#asyncio.Semaphore.release" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Release a semaphore, incrementing the internal counter by one.
|
|
Can wake up a task waiting to acquire the semaphore.</p>
|
|
<p>Unlike <a class="reference internal" href="#asyncio.BoundedSemaphore" title="asyncio.BoundedSemaphore"><code class="xref py py-class docutils literal notranslate"><span class="pre">BoundedSemaphore</span></code></a>, <a class="reference internal" href="#asyncio.Semaphore" title="asyncio.Semaphore"><code class="xref py py-class docutils literal notranslate"><span class="pre">Semaphore</span></code></a> allows
|
|
making more <code class="docutils literal notranslate"><span class="pre">release()</span></code> calls than <code class="docutils literal notranslate"><span class="pre">acquire()</span></code> calls.</p>
|
|
</dd></dl>
|
|
|
|
</dd></dl>
|
|
|
|
</section>
|
|
<section id="boundedsemaphore">
|
|
<h2>BoundedSemaphore<a class="headerlink" href="#boundedsemaphore" title="Link to this heading">¶</a></h2>
|
|
<dl class="py class">
|
|
<dt class="sig sig-object py" id="asyncio.BoundedSemaphore">
|
|
<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">asyncio.</span></span><span class="sig-name descname"><span class="pre">BoundedSemaphore</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</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="#asyncio.BoundedSemaphore" title="Link to this definition">¶</a></dt>
|
|
<dd><p>A bounded semaphore object. Not thread-safe.</p>
|
|
<p>Bounded Semaphore is a version of <a class="reference internal" href="#asyncio.Semaphore" title="asyncio.Semaphore"><code class="xref py py-class docutils literal notranslate"><span class="pre">Semaphore</span></code></a> that 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> in <a class="reference internal" href="#asyncio.Semaphore.release" title="asyncio.Semaphore.release"><code class="xref py py-meth docutils literal notranslate"><span class="pre">release()</span></code></a> if it
|
|
increases the internal counter above the initial <em>value</em>.</p>
|
|
<div class="versionchanged">
|
|
<p><span class="versionmodified changed">Changed in version 3.10: </span>Removed the <em>loop</em> parameter.</p>
|
|
</div>
|
|
</dd></dl>
|
|
|
|
</section>
|
|
<section id="barrier">
|
|
<h2>Barrier<a class="headerlink" href="#barrier" title="Link to this heading">¶</a></h2>
|
|
<dl class="py class">
|
|
<dt class="sig sig-object py" id="asyncio.Barrier">
|
|
<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">asyncio.</span></span><span class="sig-name descname"><span class="pre">Barrier</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">parties</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Barrier" title="Link to this definition">¶</a></dt>
|
|
<dd><p>A barrier object. Not thread-safe.</p>
|
|
<p>A barrier is a simple synchronization primitive that allows to block until
|
|
<em>parties</em> number of tasks are waiting on it.
|
|
Tasks can wait on the <a class="reference internal" href="#asyncio.Barrier.wait" title="asyncio.Barrier.wait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">wait()</span></code></a> method and would be blocked until
|
|
the specified number of tasks end up waiting on <a class="reference internal" href="#asyncio.Barrier.wait" title="asyncio.Barrier.wait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">wait()</span></code></a>.
|
|
At that point all of the waiting tasks would unblock simultaneously.</p>
|
|
<p><a class="reference internal" href="../reference/compound_stmts.html#async-with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">with</span></code></a> can be used as an alternative to awaiting on
|
|
<a class="reference internal" href="#asyncio.Barrier.wait" title="asyncio.Barrier.wait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">wait()</span></code></a>.</p>
|
|
<p>The barrier can be reused any number of times.</p>
|
|
<p id="asyncio-example-barrier">Example:</p>
|
|
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">example_barrier</span><span class="p">():</span>
|
|
<span class="c1"># barrier with 3 parties</span>
|
|
<span class="n">b</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">Barrier</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
|
|
|
|
<span class="c1"># create 2 new waiting tasks</span>
|
|
<span class="n">asyncio</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span><span class="n">b</span><span class="o">.</span><span class="n">wait</span><span class="p">())</span>
|
|
<span class="n">asyncio</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span><span class="n">b</span><span class="o">.</span><span class="n">wait</span><span class="p">())</span>
|
|
|
|
<span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
|
|
<span class="nb">print</span><span class="p">(</span><span class="n">b</span><span class="p">)</span>
|
|
|
|
<span class="c1"># The third .wait() call passes the barrier</span>
|
|
<span class="k">await</span> <span class="n">b</span><span class="o">.</span><span class="n">wait</span><span class="p">()</span>
|
|
<span class="nb">print</span><span class="p">(</span><span class="n">b</span><span class="p">)</span>
|
|
<span class="nb">print</span><span class="p">(</span><span class="s2">"barrier passed"</span><span class="p">)</span>
|
|
|
|
<span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
|
|
<span class="nb">print</span><span class="p">(</span><span class="n">b</span><span class="p">)</span>
|
|
|
|
<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">example_barrier</span><span class="p">())</span>
|
|
</pre></div>
|
|
</div>
|
|
<p>Result of this example is:</p>
|
|
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="o"><</span><span class="n">asyncio</span><span class="o">.</span><span class="n">locks</span><span class="o">.</span><span class="n">Barrier</span> <span class="nb">object</span> <span class="n">at</span> <span class="mi">0</span><span class="n">x</span><span class="o">...</span> <span class="p">[</span><span class="n">filling</span><span class="p">,</span> <span class="n">waiters</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="mi">3</span><span class="p">]</span><span class="o">></span>
|
|
<span class="o"><</span><span class="n">asyncio</span><span class="o">.</span><span class="n">locks</span><span class="o">.</span><span class="n">Barrier</span> <span class="nb">object</span> <span class="n">at</span> <span class="mi">0</span><span class="n">x</span><span class="o">...</span> <span class="p">[</span><span class="n">draining</span><span class="p">,</span> <span class="n">waiters</span><span class="p">:</span><span class="mi">0</span><span class="o">/</span><span class="mi">3</span><span class="p">]</span><span class="o">></span>
|
|
<span class="n">barrier</span> <span class="n">passed</span>
|
|
<span class="o"><</span><span class="n">asyncio</span><span class="o">.</span><span class="n">locks</span><span class="o">.</span><span class="n">Barrier</span> <span class="nb">object</span> <span class="n">at</span> <span class="mi">0</span><span class="n">x</span><span class="o">...</span> <span class="p">[</span><span class="n">filling</span><span class="p">,</span> <span class="n">waiters</span><span class="p">:</span><span class="mi">0</span><span class="o">/</span><span class="mi">3</span><span class="p">]</span><span class="o">></span>
|
|
</pre></div>
|
|
</div>
|
|
<div class="versionadded">
|
|
<p><span class="versionmodified added">Added in version 3.11.</span></p>
|
|
</div>
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Barrier.wait">
|
|
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">wait</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Barrier.wait" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Pass the barrier. When all the tasks party to the barrier have called
|
|
this function, they are all unblocked simultaneously.</p>
|
|
<p>When a waiting or blocked task in the barrier is cancelled,
|
|
this task exits the barrier which stays in the same state.
|
|
If the state of the barrier is “filling”, the number of waiting task
|
|
decreases by 1.</p>
|
|
<p>The return value is an integer in the range of 0 to <code class="docutils literal notranslate"><span class="pre">parties-1</span></code>, different
|
|
for each task. This can be used to select a task to do some special
|
|
housekeeping, e.g.:</p>
|
|
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="o">...</span>
|
|
<span class="k">async</span> <span class="k">with</span> <span class="n">barrier</span> <span class="k">as</span> <span class="n">position</span><span class="p">:</span>
|
|
<span class="k">if</span> <span class="n">position</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
|
|
<span class="c1"># Only one task prints this</span>
|
|
<span class="nb">print</span><span class="p">(</span><span class="s1">'End of *draining phase*'</span><span class="p">)</span>
|
|
</pre></div>
|
|
</div>
|
|
<p>This method may raise a <a class="reference internal" href="#asyncio.BrokenBarrierError" title="asyncio.BrokenBarrierError"><code class="xref py py-class docutils literal notranslate"><span class="pre">BrokenBarrierError</span></code></a> exception if the
|
|
barrier is broken or reset while a task is waiting.
|
|
It could raise a <a class="reference internal" href="asyncio-exceptions.html#asyncio.CancelledError" title="asyncio.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a> if a task is cancelled.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Barrier.reset">
|
|
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">reset</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Barrier.reset" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Return the barrier to the default, empty state. Any tasks waiting on it
|
|
will receive the <a class="reference internal" href="#asyncio.BrokenBarrierError" title="asyncio.BrokenBarrierError"><code class="xref py py-class docutils literal notranslate"><span class="pre">BrokenBarrierError</span></code></a> exception.</p>
|
|
<p>If a barrier is broken it may be better to just leave it and create a new one.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py method">
|
|
<dt class="sig sig-object py" id="asyncio.Barrier.abort">
|
|
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-name descname"><span class="pre">abort</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Barrier.abort" title="Link to this definition">¶</a></dt>
|
|
<dd><p>Put the barrier into a broken state. This causes any active or future
|
|
calls to <a class="reference internal" href="#asyncio.Barrier.wait" title="asyncio.Barrier.wait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">wait()</span></code></a> to fail with the <a class="reference internal" href="#asyncio.BrokenBarrierError" title="asyncio.BrokenBarrierError"><code class="xref py py-class docutils literal notranslate"><span class="pre">BrokenBarrierError</span></code></a>.
|
|
Use this for example if one of the tasks needs to abort, to avoid infinite
|
|
waiting tasks.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py attribute">
|
|
<dt class="sig sig-object py" id="asyncio.Barrier.parties">
|
|
<span class="sig-name descname"><span class="pre">parties</span></span><a class="headerlink" href="#asyncio.Barrier.parties" title="Link to this definition">¶</a></dt>
|
|
<dd><p>The number of tasks required to pass the barrier.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py attribute">
|
|
<dt class="sig sig-object py" id="asyncio.Barrier.n_waiting">
|
|
<span class="sig-name descname"><span class="pre">n_waiting</span></span><a class="headerlink" href="#asyncio.Barrier.n_waiting" title="Link to this definition">¶</a></dt>
|
|
<dd><p>The number of tasks currently waiting in the barrier while filling.</p>
|
|
</dd></dl>
|
|
|
|
<dl class="py attribute">
|
|
<dt class="sig sig-object py" id="asyncio.Barrier.broken">
|
|
<span class="sig-name descname"><span class="pre">broken</span></span><a class="headerlink" href="#asyncio.Barrier.broken" title="Link to this definition">¶</a></dt>
|
|
<dd><p>A boolean that is <code class="docutils literal notranslate"><span class="pre">True</span></code> if the barrier is in the broken state.</p>
|
|
</dd></dl>
|
|
|
|
</dd></dl>
|
|
|
|
<dl class="py exception">
|
|
<dt class="sig sig-object py" id="asyncio.BrokenBarrierError">
|
|
<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">asyncio.</span></span><span class="sig-name descname"><span class="pre">BrokenBarrierError</span></span><a class="headerlink" href="#asyncio.BrokenBarrierError" title="Link to this definition">¶</a></dt>
|
|
<dd><p>This exception, a subclass of <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 when the
|
|
<a class="reference internal" href="#asyncio.Barrier" title="asyncio.Barrier"><code class="xref py py-class docutils literal notranslate"><span class="pre">Barrier</span></code></a> object is reset or broken.</p>
|
|
</dd></dl>
|
|
|
|
<hr class="docutils" />
|
|
<div class="versionchanged">
|
|
<p><span class="versionmodified changed">Changed in version 3.9: </span>Acquiring a lock using <code class="docutils literal notranslate"><span class="pre">await</span> <span class="pre">lock</span></code> or <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span> <span class="pre">lock</span></code> and/or
|
|
<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 (<code class="docutils literal notranslate"><span class="pre">with</span> <span class="pre">await</span> <span class="pre">lock</span></code>, <code class="docutils literal notranslate"><span class="pre">with</span> <span class="pre">(yield</span> <span class="pre">from</span>
|
|
<span class="pre">lock)</span></code>) was removed. Use <code class="docutils literal notranslate"><span class="pre">async</span> <span class="pre">with</span> <span class="pre">lock</span></code> instead.</p>
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