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<span id="run-subprocess-with-callback"></span><h1>run_subprocess_with_callback<a class="headerlink" href="#module-edifice" title="Link to this heading">#</a></h1>
<dl class="py function">
<dt class="sig sig-object py" id="edifice.run_subprocess_with_callback">
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">edifice.</span></span><span class="sig-name descname"><span class="pre">run_subprocess_with_callback</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">subprocess</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">callback</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">daemon</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="reference internal" href="_modules/edifice/run_subprocess_with_callback.html#run_subprocess_with_callback"><span class="viewcode-link"><span class="pre">[source]</span></span></a><a class="headerlink" href="#edifice.run_subprocess_with_callback" title="Link to this definition">#</a></dt>
<dd><p>Run a
<code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> function in a
<a class="reference external" href="https://docs.python.org/3/library/multiprocessing.html#multiprocessing.Process">Process</a>
and return the result.</p>
<dl class="field-list simple">
<dt class="field-odd">Parameters<span class="colon">:</span></dt>
<dd class="field-odd"><ul class="simple">
<li><p><strong>subprocess</strong> (<span class="sphinx_autodoc_typehints-type"><code class="xref py py-data docutils literal notranslate"><span class="pre">Callable</span></code>[[<code class="xref py py-data docutils literal notranslate"><span class="pre">Callable</span></code>[[<code class="xref py py-class docutils literal notranslate"><span class="pre">ParamSpec</span></code>(<code class="docutils literal notranslate"><span class="pre">_P_callback</span></code>)], <code class="xref py py-obj docutils literal notranslate"><span class="pre">None</span></code>]], <code class="xref py py-class docutils literal notranslate"><span class="pre">TypeVar</span></code>(<code class="docutils literal notranslate"><span class="pre">_T_subprocess</span></code>)]</span>) – <p>The function to run in a
<a class="reference external" href="https://docs.python.org/3/library/multiprocessing.html#multiprocessing.Process">Process</a>.
This <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> function takes a single argument: a function with the same type
as the <code class="code docutils literal notranslate"><span class="pre">callback</span></code> function.
The <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> function must be picklable.</p>
</p></li>
<li><p><strong>callback</strong> (<span class="sphinx_autodoc_typehints-type"><code class="xref py py-data docutils literal notranslate"><span class="pre">Callable</span></code>[[<code class="xref py py-class docutils literal notranslate"><span class="pre">ParamSpec</span></code>(<code class="docutils literal notranslate"><span class="pre">_P_callback</span></code>)], <code class="xref py py-obj docutils literal notranslate"><span class="pre">None</span></code>]</span>) – The <code class="code docutils literal notranslate"><span class="pre">callback</span></code> function to pass to the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> when it starts.
The <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> may call the <code class="code docutils literal notranslate"><span class="pre">callback</span></code> function
at any time.
The <code class="code docutils literal notranslate"><span class="pre">callback</span></code> function will run in the main process event loop.
All of the arguments to the <code class="code docutils literal notranslate"><span class="pre">callback</span></code> function must be picklable.</p></li>
<li><p><strong>daemon</strong> (<span class="sphinx_autodoc_typehints-type"><code class="xref py py-data docutils literal notranslate"><span class="pre">Optional</span></code>[<code class="xref py py-class docutils literal notranslate"><span class="pre">bool</span></code>]</span>) – Optional argument which will be passed to the Process
<a class="reference external" href="https://docs.python.org/3/library/multiprocessing.html#multiprocessing.Process.daemon">daemon</a>
argument.</p></li>
</ul>
</dd>
<dt class="field-even">Return type<span class="colon">:</span></dt>
<dd class="field-even"><p><span class="sphinx_autodoc_typehints-type"><code class="xref py py-class docutils literal notranslate"><span class="pre">TypeVar</span></code>(<code class="docutils literal notranslate"><span class="pre">_T_subprocess</span></code>)</span></p>
</dd>
</dl>
<p>The advantage of <a class="reference internal" href="#edifice.run_subprocess_with_callback" title="edifice.run_subprocess_with_callback"><code class="xref py py-func docutils literal notranslate"><span class="pre">run_subprocess_with_callback()</span></code></a> over
<a class="reference external" href="https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.loop.run_in_executor">run_in_executor</a>
<a class="reference external" href="https://docs.python.org/3/library/concurrent.futures.html#concurrent.futures.ProcessPoolExecutor">ProcessPoolExecutor</a>
is that <a class="reference internal" href="#edifice.run_subprocess_with_callback" title="edifice.run_subprocess_with_callback"><code class="xref py py-func docutils literal notranslate"><span class="pre">run_subprocess_with_callback()</span></code></a> behaves
well and cleans up properly in the event of
<a class="reference external" href="https://docs.python.org/3/library/asyncio-task.html#task-cancellation">cancellation</a>,
exceptions, and crashes.
<a class="reference external" href="https://discuss.python.org/t/cancel-running-work-in-processpoolexecutor/58605">ProcessPoolExecutor cannot be cancelled.</a>.
This function is useful for a CPU-bound parallel worker
subprocess for which we want to report progress back to the main GUI event loop.
Like <em>PyTorch</em> stuff.</p>
<p>The <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> will be started when <code class="code docutils literal notranslate"><span class="pre">await</span></code> <a class="reference internal" href="#edifice.run_subprocess_with_callback" title="edifice.run_subprocess_with_callback"><code class="xref py py-func docutils literal notranslate"><span class="pre">run_subprocess_with_callback()</span></code></a>
is entered, and the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> is guaranteed to be terminated when
<code class="code docutils literal notranslate"><span class="pre">await</span></code> <a class="reference internal" href="#edifice.run_subprocess_with_callback" title="edifice.run_subprocess_with_callback"><code class="xref py py-func docutils literal notranslate"><span class="pre">run_subprocess_with_callback()</span></code></a> completes.</p>
<p>While the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> is running, it may call the supplied <code class="code docutils literal notranslate"><span class="pre">callback</span></code> function.
The <code class="code docutils literal notranslate"><span class="pre">callback</span></code> function will run in the main event loop of the calling process.</p>
<p>The <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> will be started with the
<a class="reference external" href="https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods">“spawn” start method</a>,
so it will not inherit any file handles from the calling process.</p>
<div class="literal-block-wrapper docutils container" id="id6">
<div class="code-block-caption"><span class="caption-text">Example</span><a class="headerlink" href="#id6" title="Link to this code">#</a></div>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">my_subprocess</span><span class="p">(</span><span class="n">callback</span><span class="p">:</span> <span class="n">Callable</span><span class="p">[[</span><span class="nb">int</span><span class="p">],</span> <span class="kc">None</span><span class="p">])</span> <span class="o">-></span> <span class="nb">str</span><span class="p">:</span>
<span class="c1"># This function will run in a new Process.</span>
<span class="n">callback</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="n">time</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">callback</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
<span class="n">time</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">callback</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="k">return</span> <span class="s2">"done"</span>
<span class="k">def</span> <span class="nf">my_callback</span><span class="p">(</span><span class="n">x</span><span class="p">:</span><span class="nb">int</span><span class="p">)</span> <span class="o">-></span> <span class="kc">None</span><span class="p">:</span>
<span class="c1"># This function will run in the main process event loop.</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"callback </span><span class="si">{</span><span class="n">x</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">()</span> <span class="o">-></span> <span class="kc">None</span><span class="p">:</span>
<span class="n">y</span> <span class="o">=</span> <span class="k">await</span> <span class="n">run_subprocess_with_callback</span><span class="p">(</span><span class="n">my_subprocess</span><span class="p">,</span> <span class="n">my_callback</span><span class="p">)</span>
<span class="c1"># If this main() function is cancelled while awaiting</span>
<span class="c1"># run_subprocess_with_callback then the subprocess will be terminated.</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"my_subprocess returned </span><span class="si">{</span><span class="n">y</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
</pre></div>
</div>
</div>
<section id="cancellation-exceptions-crashes">
<h2>Cancellation, Exceptions, Crashes<a class="headerlink" href="#cancellation-exceptions-crashes" title="Link to this heading">#</a></h2>
<p>If this <code class="code docutils literal notranslate"><span class="pre">async</span></code> <a class="reference internal" href="#edifice.run_subprocess_with_callback" title="edifice.run_subprocess_with_callback"><code class="xref py py-func docutils literal notranslate"><span class="pre">run_subprocess_with_callback()</span></code></a> function is
<a class="reference external" href="https://docs.python.org/3/library/asyncio-task.html#task-cancellation">cancelled</a>,
then the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> will be terminated by calling
<a class="reference external" href="https://docs.python.org/3/library/multiprocessing.html#multiprocessing.Process.terminate">Process.terminate()</a>.
Termination of the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> will occur even if
the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> is blocked. Note that
<a class="reference external" href="https://docs.python.org/3/library/asyncio-exceptions.html#asyncio.CancelledError">CancelledError</a>
will not be raised in the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code>,
instead the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> will be terminated immediately. If you
want to perform sudden cleanup and halt of the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> then
send it a message as in the below <cite>Example of Queue messaging.</cite></p>
<p>Exceptions raised in the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> will be re-raised from <a class="reference internal" href="#edifice.run_subprocess_with_callback" title="edifice.run_subprocess_with_callback"><code class="xref py py-func docutils literal notranslate"><span class="pre">run_subprocess_with_callback()</span></code></a>,
including
<a class="reference external" href="https://docs.python.org/3/library/asyncio-exceptions.html#asyncio.CancelledError">CancelledError</a>.
Because the Exception must be pickled back to the main process, it will
lose its <a class="reference external" href="https://docs.python.org/3/reference/datamodel.html#traceback-objects">traceback</a>.
In Python ≥3.11, the traceback string from the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> stack will be added
to the Exception <a class="reference external" href="https://docs.python.org/3/library/exceptions.html#BaseException.__notes__">__notes__</a>.</p>
<p>Exceptions raised in the <code class="code docutils literal notranslate"><span class="pre">callback</span></code> will be suppressed.</p>
<p>If the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> exits abnormally without returning a value then a
<a class="reference external" href="https://docs.python.org/3/library/multiprocessing.html#multiprocessing.ProcessError">ProcessError</a>
will be raised from <a class="reference internal" href="#edifice.run_subprocess_with_callback" title="edifice.run_subprocess_with_callback"><code class="xref py py-func docutils literal notranslate"><span class="pre">run_subprocess_with_callback()</span></code></a>.</p>
</section>
<section id="pickling-the-subprocess">
<h2>Pickling the subprocess<a class="headerlink" href="#pickling-the-subprocess" title="Link to this heading">#</a></h2>
<p>Because “only picklable objects can be executed” by a
<a class="reference external" href="https://docs.python.org/3/library/multiprocessing.html#multiprocessing.Process">Process</a>.
we cannot pass a local function with local variable bindings
as the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code>. The best workaround is to define at the module
top-level a <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> function which takes all its parameters as
arguments, and then use
<a class="reference external" href="https://docs.python.org/3/library/functools.html#functools.partial">functools.partial</a>
to bind local values to the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> parameters.
See below <cite>Example of Queue messaging.</cite></p>
<p>The <code class="code docutils literal notranslate"><span class="pre">callback</span></code> does not have this problem; we can pass a local
function as the <code class="code docutils literal notranslate"><span class="pre">callback</span></code>.</p>
</section>
<section id="messaging-to-the-subprocess">
<h2>Messaging to the subprocess<a class="headerlink" href="#messaging-to-the-subprocess" title="Link to this heading">#</a></h2>
<p>The <a class="reference internal" href="#edifice.run_subprocess_with_callback" title="edifice.run_subprocess_with_callback"><code class="xref py py-func docutils literal notranslate"><span class="pre">run_subprocess_with_callback()</span></code></a> function provides a <code class="code docutils literal notranslate"><span class="pre">callback</span></code>
function for messaging back up to the main process, but it does not provide a
built-in way to message down to the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code>.</p>
<p>To message down to the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> we can create
and pass a messaging object to the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code>, for example a
<a class="reference external" href="https://docs.python.org/3/library/multiprocessing.html#multiprocessing.Queue">multiprocessing.Queue</a>.</p>
<p>Because the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> is started in the
<a class="reference external" href="https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods">“spawn” context</a>,
we must create the <code class="code docutils literal notranslate"><span class="pre">Queue</span></code> in the <code class="code docutils literal notranslate"><span class="pre">"spawn"</span></code> context.</p>
<div class="literal-block-wrapper docutils container" id="id7">
<div class="code-block-caption"><span class="caption-text">Example of Queue messaging from the main process to the subprocess</span><a class="headerlink" href="#id7" title="Link to this code">#</a></div>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">my_subprocess</span><span class="p">(</span>
<span class="c1"># This function will run in a new Process.</span>
<span class="n">msg_queue</span><span class="p">:</span> <span class="n">multiprocessing</span><span class="o">.</span><span class="n">queues</span><span class="o">.</span><span class="n">Queue</span><span class="p">[</span><span class="nb">str</span><span class="p">],</span>
<span class="n">callback</span><span class="p">:</span> <span class="n">typing</span><span class="o">.</span><span class="n">Callable</span><span class="p">[[</span><span class="nb">int</span><span class="p">],</span> <span class="kc">None</span><span class="p">],</span>
<span class="p">)</span> <span class="o">-></span> <span class="nb">str</span><span class="p">:</span>
<span class="k">while</span> <span class="p">(</span><span class="n">msg</span> <span class="o">:=</span> <span class="n">msg_queue</span><span class="o">.</span><span class="n">get</span><span class="p">())</span> <span class="o">!=</span> <span class="s2">"finish"</span><span class="p">:</span>
<span class="n">callback</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">msg</span><span class="p">))</span>
<span class="k">return</span> <span class="s2">"done"</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">()</span> <span class="o">-></span> <span class="kc">None</span><span class="p">:</span>
<span class="n">msg_queue</span><span class="p">:</span> <span class="n">multiprocessing</span><span class="o">.</span><span class="n">queues</span><span class="o">.</span><span class="n">Queue</span><span class="p">[</span><span class="nb">str</span><span class="p">]</span> <span class="o">=</span> <span class="n">multiprocessing</span><span class="o">.</span><span class="n">get_context</span><span class="p">(</span><span class="s2">"spawn"</span><span class="p">)</span><span class="o">.</span><span class="n">Queue</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">local_callback</span><span class="p">(</span><span class="n">x</span><span class="p">:</span><span class="nb">int</span><span class="p">)</span> <span class="o">-></span> <span class="kc">None</span><span class="p">:</span>
<span class="c1"># This function will run in the main process event loop.</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"callback </span><span class="si">{</span><span class="n">x</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">send_messages</span><span class="p">()</span> <span class="o">-></span> <span class="kc">None</span><span class="p">:</span>
<span class="n">msg_queue</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="s2">"one"</span><span class="p">)</span>
<span class="n">msg_queue</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="s2">"finish"</span><span class="p">)</span>
<span class="c1"># In this example we use gather() to run these 2 functions</span>
<span class="c1"># concurrently (“at the same time”).</span>
<span class="c1">#</span>
<span class="c1"># 1. run_subprocess_with_callback()</span>
<span class="c1"># 2. send_messages()</span>
<span class="c1">#</span>
<span class="c1"># In your code you will probably instead want to send_messages()</span>
<span class="c1"># in reaction to some event.</span>
<span class="c1">#</span>
<span class="n">y</span><span class="p">,</span> <span class="n">_</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">gather</span><span class="p">(</span>
<span class="n">run_subprocess_with_callback</span><span class="p">(</span>
<span class="n">functools</span><span class="o">.</span><span class="n">partial</span><span class="p">(</span><span class="n">my_subprocess</span><span class="p">,</span> <span class="n">msg_queue</span><span class="p">),</span>
<span class="n">local_callback</span><span class="p">,</span>
<span class="p">),</span>
<span class="n">send_messages</span><span class="p">(),</span>
<span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"my_subprocess returned </span><span class="si">{</span><span class="n">y</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>To get proper type hinting on the <code class="code docutils literal notranslate"><span class="pre">Queue</span></code>:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">__future__</span> <span class="kn">import</span> <span class="n">annotations</span>
</pre></div>
</div>
</div>
</section>
<section id="async-in-the-subprocess">
<h2>Async in the subprocess<a class="headerlink" href="#async-in-the-subprocess" title="Link to this heading">#</a></h2>
<p>If you want the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> to run an <code class="code docutils literal notranslate"><span class="pre">async</span></code> function then
make a new event loop and use that as the event loop in the
<code class="code docutils literal notranslate"><span class="pre">subprocess</span></code>.</p>
<div class="literal-block-wrapper docutils container" id="id8">
<div class="code-block-caption"><span class="caption-text">Example async subprocess function</span><a class="headerlink" href="#id8" title="Link to this code">#</a></div>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">my_subprocess</span><span class="p">(</span><span class="n">callback</span><span class="p">:</span> <span class="n">typing</span><span class="o">.</span><span class="n">Callable</span><span class="p">[[</span><span class="nb">int</span><span class="p">],</span> <span class="kc">None</span><span class="p">])</span> <span class="o">-></span> <span class="nb">str</span><span class="p">:</span>
<span class="c1"># This function will run in a new Process.</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">work</span><span class="p">()</span> <span class="o">-></span> <span class="nb">str</span><span class="p">:</span>
<span class="n">callback</span><span class="p">(</span><span class="mi">1</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">1</span><span class="p">)</span>
<span class="k">return</span> <span class="s2">"done"</span>
<span class="k">return</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">new_event_loop</span><span class="p">()</span><span class="o">.</span><span class="n">run_until_complete</span><span class="p">(</span><span class="n">work</span><span class="p">())</span>
</pre></div>
</div>
</div>
<p>A cancelled <code class="code docutils literal notranslate"><span class="pre">await</span></code> in the <code class="code docutils literal notranslate"><span class="pre">subprocess</span></code> will raise
<a class="reference external" href="https://docs.python.org/3/library/asyncio-exceptions.html#asyncio.CancelledError">CancelledError</a>
which will be propagated and re-raised from
<a class="reference internal" href="#edifice.run_subprocess_with_callback" title="edifice.run_subprocess_with_callback"><code class="xref py py-func docutils literal notranslate"><span class="pre">run_subprocess_with_callback()</span></code></a> in the usual way.</p>
</section>
<section id="pyinstaller">
<h2>PyInstaller<a class="headerlink" href="#pyinstaller" title="Link to this heading">#</a></h2>
<p>If you build a distribution with <a class="reference external" href="https://pyinstaller.org/">PyInstaller</a>
then you should call
<a class="reference external" href="https://docs.python.org/3/library/multiprocessing.html#multiprocessing.freeze_support">multiprocessing.freeze_support()</a>
to divert the spawn Process
<a class="reference external" href="https://pyinstaller.org/en/stable/common-issues-and-pitfalls.html#when-to-call-multiprocessing-freeze-support">before the __main__ imports</a>
so that the spawn Process starts up faster.</p>
</section>
<section id="independence">
<h2>Independence<a class="headerlink" href="#independence" title="Link to this heading">#</a></h2>
<p>This <a class="reference internal" href="#edifice.run_subprocess_with_callback" title="edifice.run_subprocess_with_callback"><code class="xref py py-func docutils literal notranslate"><span class="pre">run_subprocess_with_callback()</span></code></a> module depends only on the
Python standard library so this module file can be copied and pasted into
another project without depending on the Edifice package.</p>
</section>
</dd></dl>
</section>
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