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<li><a class="reference internal" href="#">Synchronization Primitives</a><ul>
<li><a class="reference internal" href="#lock">Lock</a></li>
<li><a class="reference internal" href="#event">Event</a></li>
<li><a class="reference internal" href="#condition">Condition</a></li>
<li><a class="reference internal" href="#semaphore">Semaphore</a></li>
<li><a class="reference internal" href="#boundedsemaphore">BoundedSemaphore</a></li>
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 <section id="synchronization-primitives">
<h1>Synchronization Primitives<a class="headerlink" href="#synchronization-primitives" title="Permalink to this headline">¶</a></h1>
Source code: <a class="reference external" href="https://github.com/python/cpython/tree/3.10/Lib/asyncio/locks.py">Lib/asyncio/locks.py</a>
<hr class="docutils" />
asyncio synchronization primitives are designed to be similar to
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">threading</code></a> module with two important caveats:
<ul class="simple">
<li>asyncio primitives are not thread-safe, therefore they should not
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">threading</code></a> for
that);</li>
<li>methods of these synchronization primitives do not accept the timeout
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">asyncio.wait_for()</code></a> function to perform
operations with timeouts.</li>
</ul>
asyncio has the following basic synchronization primitives:
<ul class="simple">
<li><a class="reference internal" href="#asyncio.Lock" title="asyncio.Lock"><code class="xref py py-class docutils literal notranslate">Lock</code></a></li>
<li><a class="reference internal" href="#asyncio.Event" title="asyncio.Event"><code class="xref py py-class docutils literal notranslate">Event</code></a></li>
<li><a class="reference internal" href="#asyncio.Condition" title="asyncio.Condition"><code class="xref py py-class docutils literal notranslate">Condition</code></a></li>
<li><a class="reference internal" href="#asyncio.Semaphore" title="asyncio.Semaphore"><code class="xref py py-class docutils literal notranslate">Semaphore</code></a></li>
<li><a class="reference internal" href="#asyncio.BoundedSemaphore" title="asyncio.BoundedSemaphore"><code class="xref py py-class docutils literal notranslate">BoundedSemaphore</code></a></li>
</ul>
<hr class="docutils" />
<section id="lock">
<h2>Lock<a class="headerlink" href="#lock" title="Permalink to this headline">¶</a></h2>
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.Lock">
class asyncio.Lock<a class="headerlink" href="#asyncio.Lock" title="Permalink to this definition">¶</a></dt>
<dd>Implements a mutex lock for asyncio tasks. Not thread-safe.
An asyncio lock can be used to guarantee exclusive access to a
shared resource.
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">async with</code></a>
statement:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>lock = asyncio.Lock()

# ... later
async with lock:
 # access shared state
</pre></div>
</div>
which is equivalent to:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>lock = asyncio.Lock()

# ... later
await lock.acquire()
try:
 # access shared state
finally:
 lock.release()
</pre></div>
</div>
<div class="versionchanged">
Changed in version 3.10: Removed the loop parameter.
</div>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Lock.acquire">
coroutine acquire()<a class="headerlink" href="#asyncio.Lock.acquire" title="Permalink to this definition">¶</a></dt>
<dd>Acquire the lock.
This method waits until the lock is unlocked, sets it to
locked and returns <code class="docutils literal notranslate">True</code>.
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">acquire()</code></a>
waiting for the lock to be unlocked, only one coroutine
eventually proceeds.
Acquiring a lock is fair: the coroutine that proceeds will be
the first coroutine that started waiting on the lock.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Lock.release">
release()<a class="headerlink" href="#asyncio.Lock.release" title="Permalink to this definition">¶</a></dt>
<dd>Release the lock.
When the lock is locked, reset it to unlocked and return.
If the lock is unlocked, a <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate">RuntimeError</code></a> is raised.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Lock.locked">
locked()<a class="headerlink" href="#asyncio.Lock.locked" title="Permalink to this definition">¶</a></dt>
<dd>Return <code class="docutils literal notranslate">True</code> if the lock is locked.
</dd></dl>

</dd></dl>

</section>
<section id="event">
<h2>Event<a class="headerlink" href="#event" title="Permalink to this headline">¶</a></h2>
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.Event">
class asyncio.Event<a class="headerlink" href="#asyncio.Event" title="Permalink to this definition">¶</a></dt>
<dd>An event object. Not thread-safe.
An asyncio event can be used to notify multiple asyncio tasks
that some event has happened.
An Event object manages an internal flag that can be set to true
with the <a class="reference internal" href="#asyncio.Event.set" title="asyncio.Event.set"><code class="xref py py-meth docutils literal notranslate">set()</code></a> method and reset to false with the
<a class="reference internal" href="#asyncio.Event.clear" title="asyncio.Event.clear"><code class="xref py py-meth docutils literal notranslate">clear()</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">wait()</code></a> method blocks until the
flag is set to true. The flag is set to false initially.
<div class="versionchanged">
Changed in version 3.10: Removed the loop parameter.
</div>
Example:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>async def waiter(event):
 print(&#39;waiting for it ...&#39;)
 await event.wait()
 print(&#39;... got it!&#39;)

async def main():
 # Create an Event object.
 event = asyncio.Event()

# Spawn a Task to wait until &#39;event&#39; is set.
 waiter_task = asyncio.create_task(waiter(event))

# Sleep for 1 second and set the event.
 await asyncio.sleep(1)
 event.set()

# Wait until the waiter task is finished.
 await waiter_task

asyncio.run(main())
</pre></div>
</div>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Event.wait">
coroutine wait()<a class="headerlink" href="#asyncio.Event.wait" title="Permalink to this definition">¶</a></dt>
<dd>Wait until the event is set.
If the event is set, return <code class="docutils literal notranslate">True</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">set()</code></a>.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Event.set">
set()<a class="headerlink" href="#asyncio.Event.set" title="Permalink to this definition">¶</a></dt>
<dd>Set the event.
All tasks waiting for event to be set will be immediately
awakened.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Event.clear">
clear()<a class="headerlink" href="#asyncio.Event.clear" title="Permalink to this definition">¶</a></dt>
<dd>Clear (unset) the event.
Tasks awaiting on <a class="reference internal" href="#asyncio.Event.wait" title="asyncio.Event.wait"><code class="xref py py-meth docutils literal notranslate">wait()</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">set()</code></a> method is called again.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Event.is_set">
is_set()<a class="headerlink" href="#asyncio.Event.is_set" title="Permalink to this definition">¶</a></dt>
<dd>Return <code class="docutils literal notranslate">True</code> if the event is set.
</dd></dl>

</dd></dl>

</section>
<section id="condition">
<h2>Condition<a class="headerlink" href="#condition" title="Permalink to this headline">¶</a></h2>
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.Condition">
class asyncio.Condition(lock=None)<a class="headerlink" href="#asyncio.Condition" title="Permalink to this definition">¶</a></dt>
<dd>A Condition object. Not thread-safe.
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.
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">Event</code></a> and a <a class="reference internal" href="#asyncio.Lock" title="asyncio.Lock"><code class="xref py py-class docutils literal notranslate">Lock</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.
The optional lock argument must be a <a class="reference internal" href="#asyncio.Lock" title="asyncio.Lock"><code class="xref py py-class docutils literal notranslate">Lock</code></a> object or
<code class="docutils literal notranslate">None</code>. In the latter case a new Lock object is created
automatically.
<div class="versionchanged">
Changed in version 3.10: Removed the loop parameter.
</div>
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">async with</code></a>
statement:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>cond = asyncio.Condition()

# ... later
async with cond:
 await cond.wait()
</pre></div>
</div>
which is equivalent to:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>cond = asyncio.Condition()

# ... later
await cond.acquire()
try:
 await cond.wait()
finally:
 cond.release()
</pre></div>
</div>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Condition.acquire">
coroutine acquire()<a class="headerlink" href="#asyncio.Condition.acquire" title="Permalink to this definition">¶</a></dt>
<dd>Acquire the underlying lock.
This method waits until the underlying lock is unlocked,
sets it to locked and returns <code class="docutils literal notranslate">True</code>.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Condition.notify">
notify(n=1)<a class="headerlink" href="#asyncio.Condition.notify" title="Permalink to this definition">¶</a></dt>
<dd>Wake up at most n tasks (1 by default) waiting on this
condition. The method is no-op if no tasks are waiting.
The lock must be acquired before this method is called and
released shortly after. If called with an unlocked lock
a <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate">RuntimeError</code></a> error is raised.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Condition.locked">
locked()<a class="headerlink" href="#asyncio.Condition.locked" title="Permalink to this definition">¶</a></dt>
<dd>Return <code class="docutils literal notranslate">True</code> if the underlying lock is acquired.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Condition.notify_all">
notify_all()<a class="headerlink" href="#asyncio.Condition.notify_all" title="Permalink to this definition">¶</a></dt>
<dd>Wake up all tasks waiting on this condition.
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">notify()</code></a>, but wakes up all waiting
tasks.
The lock must be acquired before this method is called and
released shortly after. If called with an unlocked lock
a <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate">RuntimeError</code></a> error is raised.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Condition.release">
release()<a class="headerlink" href="#asyncio.Condition.release" title="Permalink to this definition">¶</a></dt>
<dd>Release the underlying lock.
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">RuntimeError</code></a> is
raised.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Condition.wait">
coroutine wait()<a class="headerlink" href="#asyncio.Condition.wait" title="Permalink to this definition">¶</a></dt>
<dd>Wait until notified.
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">RuntimeError</code></a> is raised.
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">notify()</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">notify_all()</code></a> call.
Once awakened, the Condition re-acquires its lock and this method
returns <code class="docutils literal notranslate">True</code>.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Condition.wait_for">
coroutine wait_for(predicate)<a class="headerlink" href="#asyncio.Condition.wait_for" title="Permalink to this definition">¶</a></dt>
<dd>Wait until a predicate becomes true.
The predicate must be a callable which result will be
interpreted as a boolean value. The final value is the
return value.
</dd></dl>

</dd></dl>

</section>
<section id="semaphore">
<h2>Semaphore<a class="headerlink" href="#semaphore" title="Permalink to this headline">¶</a></h2>
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.Semaphore">
class asyncio.Semaphore(value=1)<a class="headerlink" href="#asyncio.Semaphore" title="Permalink to this definition">¶</a></dt>
<dd>A Semaphore object. Not thread-safe.
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">acquire()</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">release()</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">acquire()</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">release()</code></a>.
The optional value argument gives the initial value for the
internal counter (<code class="docutils literal notranslate">1</code> by default). If the given value is
less than <code class="docutils literal notranslate">0</code> a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a> is raised.
<div class="versionchanged">
Changed in version 3.10: Removed the loop parameter.
</div>
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">async with</code></a>
statement:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>sem = asyncio.Semaphore(10)

# ... later
async with sem:
 # work with shared resource
</pre></div>
</div>
which is equivalent to:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>sem = asyncio.Semaphore(10)

# ... later
await sem.acquire()
try:
 # work with shared resource
finally:
 sem.release()
</pre></div>
</div>
<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Semaphore.acquire">
coroutine acquire()<a class="headerlink" href="#asyncio.Semaphore.acquire" title="Permalink to this definition">¶</a></dt>
<dd>Acquire a semaphore.
If the internal counter is greater than zero, decrement
it by one and return <code class="docutils literal notranslate">True</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">release()</code></a> is called and return <code class="docutils literal notranslate">True</code>.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Semaphore.locked">
locked()<a class="headerlink" href="#asyncio.Semaphore.locked" title="Permalink to this definition">¶</a></dt>
<dd>Returns <code class="docutils literal notranslate">True</code> if semaphore can not be acquired immediately.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="asyncio.Semaphore.release">
release()<a class="headerlink" href="#asyncio.Semaphore.release" title="Permalink to this definition">¶</a></dt>
<dd>Release a semaphore, incrementing the internal counter by one.
Can wake up a task waiting to acquire the semaphore.
Unlike <a class="reference internal" href="#asyncio.BoundedSemaphore" title="asyncio.BoundedSemaphore"><code class="xref py py-class docutils literal notranslate">BoundedSemaphore</code></a>, <a class="reference internal" href="#asyncio.Semaphore" title="asyncio.Semaphore"><code class="xref py py-class docutils literal notranslate">Semaphore</code></a> allows
making more <code class="docutils literal notranslate">release()</code> calls than <code class="docutils literal notranslate">acquire()</code> calls.
</dd></dl>

</dd></dl>

</section>
<section id="boundedsemaphore">
<h2>BoundedSemaphore<a class="headerlink" href="#boundedsemaphore" title="Permalink to this headline">¶</a></h2>
<dl class="py class">
<dt class="sig sig-object py" id="asyncio.BoundedSemaphore">
class asyncio.BoundedSemaphore(value=1)<a class="headerlink" href="#asyncio.BoundedSemaphore" title="Permalink to this definition">¶</a></dt>
<dd>A bounded semaphore object. Not thread-safe.
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">Semaphore</code></a> that raises
a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a> in <a class="reference internal" href="#asyncio.Semaphore.release" title="asyncio.Semaphore.release"><code class="xref py py-meth docutils literal notranslate">release()</code></a> if it
increases the internal counter above the initial value.
<div class="versionchanged">
Changed in version 3.10: Removed the loop parameter.
</div>
</dd></dl>

<hr class="docutils" />
<div class="versionchanged">
Changed in version 3.9: Acquiring a lock using <code class="docutils literal notranslate">await lock</code> or <code class="docutils literal notranslate">yield from lock</code> and/or
<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate">with</code></a> statement (<code class="docutils literal notranslate">with await lock</code>, <code class="docutils literal notranslate">with (yield from
lock)</code>) was removed. Use <code class="docutils literal notranslate">async with lock</code> instead.
</div>
</section>
</section>

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 <ul>
<li><a class="reference internal" href="#">Synchronization Primitives</a><ul>
<li><a class="reference internal" href="#lock">Lock</a></li>
<li><a class="reference internal" href="#event">Event</a></li>
<li><a class="reference internal" href="#condition">Condition</a></li>
<li><a class="reference internal" href="#semaphore">Semaphore</a></li>
<li><a class="reference internal" href="#boundedsemaphore">BoundedSemaphore</a></li>
</ul>
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