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  <section id="support-for-perf-maps">
<span id="perfmaps"></span><h1>Support for Perf Maps<a class="headerlink" href="#support-for-perf-maps" title="Permalink to this headline">¶</a></h1>
<p>On supported platforms (as of this writing, only Linux), the runtime can take
advantage of <em>perf map files</em> to make Python functions visible to an external
profiling tool (such as <a class="reference external" href="https://perf.wiki.kernel.org/index.php/Main_Page">perf</a>).
A running process may create a file in the <code class="docutils literal notranslate"><span class="pre">/tmp</span></code> directory, which contains entries
that can map a section of executable code to a name. This interface is described in the
<a class="reference external" href="https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/Documentation/jit-interface.txt">documentation of the Linux Perf tool</a>.</p>
<p>In Python, these helper APIs can be used by libraries and features that rely
on generating machine code on the fly.</p>
<p>Note that holding the Global Interpreter Lock (GIL) is not required for these APIs.</p>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyUnstable_PerfMapState_Init">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyUnstable_PerfMapState_Init</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyUnstable_PerfMapState_Init" title="Permalink to this definition">¶</a><br /></dt>
<dd><div class="unstable-c-api warning admonition">
<em>This is <a class="reference internal" href="stable.html#unstable-c-api"><span class="std std-ref">Unstable API</span></a>. It may change without warning in minor releases.</em></div>
<p>Open the <code class="docutils literal notranslate"><span class="pre">/tmp/perf-$pid.map</span></code> file, unless it’s already opened, and create
a lock to ensure thread-safe writes to the file (provided the writes are
done through <a class="reference internal" href="#c.PyUnstable_WritePerfMapEntry" title="PyUnstable_WritePerfMapEntry"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyUnstable_WritePerfMapEntry()</span></code></a>). Normally, there’s no need
to call this explicitly; just use <a class="reference internal" href="#c.PyUnstable_WritePerfMapEntry" title="PyUnstable_WritePerfMapEntry"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyUnstable_WritePerfMapEntry()</span></code></a>
and it will initialize the state on first call.</p>
<p>Returns <code class="docutils literal notranslate"><span class="pre">0</span></code> on success, <code class="docutils literal notranslate"><span class="pre">-1</span></code> on failure to create/open the perf map file,
or <code class="docutils literal notranslate"><span class="pre">-2</span></code> on failure to create a lock. Check <code class="docutils literal notranslate"><span class="pre">errno</span></code> for more information
about the cause of a failure.</p>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyUnstable_WritePerfMapEntry">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyUnstable_WritePerfMapEntry</span></span></span><span class="sig-paren">(</span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">code_addr</span></span>, <span class="kt"><span class="pre">unsigned</span></span><span class="w"> </span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">code_size</span></span>, <span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">entry_name</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyUnstable_WritePerfMapEntry" title="Permalink to this definition">¶</a><br /></dt>
<dd><div class="unstable-c-api warning admonition">
<em>This is <a class="reference internal" href="stable.html#unstable-c-api"><span class="std std-ref">Unstable API</span></a>. It may change without warning in minor releases.</em></div>
<p>Write one single entry to the <code class="docutils literal notranslate"><span class="pre">/tmp/perf-$pid.map</span></code> file. This function is
thread safe. Here is what an example entry looks like:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp"># address      size  name</span>
<span class="mf">7f3529f</span><span class="n">cf759</span><span class="w"> </span><span class="n">b</span><span class="w">     </span><span class="n">py</span><span class="o">::</span><span class="n">bar</span><span class="o">:/</span><span class="n">run</span><span class="o">/</span><span class="n">t</span><span class="p">.</span><span class="n">py</span>
</pre></div>
</div>
<p>Will call <a class="reference internal" href="#c.PyUnstable_PerfMapState_Init" title="PyUnstable_PerfMapState_Init"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyUnstable_PerfMapState_Init()</span></code></a> before writing the entry, if
the perf map file is not already opened. Returns <code class="docutils literal notranslate"><span class="pre">0</span></code> on success, or the
same error codes as <a class="reference internal" href="#c.PyUnstable_PerfMapState_Init" title="PyUnstable_PerfMapState_Init"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyUnstable_PerfMapState_Init()</span></code></a> on failure.</p>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyUnstable_PerfMapState_Fini">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyUnstable_PerfMapState_Fini</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyUnstable_PerfMapState_Fini" title="Permalink to this definition">¶</a><br /></dt>
<dd><div class="unstable-c-api warning admonition">
<em>This is <a class="reference internal" href="stable.html#unstable-c-api"><span class="std std-ref">Unstable API</span></a>. It may change without warning in minor releases.</em></div>
<p>Close the perf map file opened by <a class="reference internal" href="#c.PyUnstable_PerfMapState_Init" title="PyUnstable_PerfMapState_Init"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyUnstable_PerfMapState_Init()</span></code></a>.
This is called by the runtime itself during interpreter shut-down. In
general, there shouldn’t be a reason to explicitly call this, except to
handle specific scenarios such as forking.</p>
</dd></dl>

</section>


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