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<section id="platform-support">
<span id="asyncio-platform-support"></span><h1>平台支持<a class="headerlink" href="#platform-support" title="永久链接至标题"></a></h1>
<p><a class="reference internal" href="asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O."><code class="xref py py-mod docutils literal notranslate"><span class="pre">asyncio</span></code></a> 模块被设计为可移植的,但由于平台的底层架构和功能,一些平台存在细微的差异和限制。</p>
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<h2>所有平台<a class="headerlink" href="#all-platforms" title="永久链接至标题"></a></h2>
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<li><p><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_reader" title="asyncio.loop.add_reader"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_reader()</span></code></a><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_writer" title="asyncio.loop.add_writer"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_writer()</span></code></a> 不能用来监视文件I/O。</p></li>
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<section id="windows">
<h2>Windows<a class="headerlink" href="#windows" title="永久链接至标题"></a></h2>
<p><strong>源代码:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.8/Lib/asyncio/proactor_events.py">Lib/asyncio/proactor_events.py</a>, <a class="reference external" href="https://github.com/python/cpython/tree/3.8/Lib/asyncio/windows_events.py">Lib/asyncio/windows_events.py</a>, <a class="reference external" href="https://github.com/python/cpython/tree/3.8/Lib/asyncio/windows_utils.py">Lib/asyncio/windows_utils.py</a></p>
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<p><span class="versionmodified changed">在 3.8 版更改: </span>在 Windows 上,<a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> 现在是默认的事件循环。</p>
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<p>Windows上的所有事件循环都不支持以下方法:</p>
<ul class="simple">
<li><p>不支持 <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_unix_connection" title="asyncio.loop.create_unix_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_unix_connection()</span></code></a><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_unix_server" title="asyncio.loop.create_unix_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_unix_server()</span></code></a><a class="reference internal" href="socket.html#socket.AF_UNIX" title="socket.AF_UNIX"><code class="xref py py-data docutils literal notranslate"><span class="pre">socket.AF_UNIX</span></code></a> 套接字相关参数仅限于Unix。</p></li>
<li><p>不支持 <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_signal_handler" title="asyncio.loop.add_signal_handler"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_signal_handler()</span></code></a><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.remove_signal_handler" title="asyncio.loop.remove_signal_handler"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.remove_signal_handler()</span></code></a></p></li>
</ul>
<p><a class="reference internal" href="asyncio-eventloop.html#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorEventLoop</span></code></a> 有下列限制:</p>
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<li><p><a class="reference internal" href="selectors.html#selectors.SelectSelector" title="selectors.SelectSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectSelector</span></code></a> 只被用于等待套接字事件它支持套接字且最多支持512个套接字。</p></li>
<li><p><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_reader" title="asyncio.loop.add_reader"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_reader()</span></code></a><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_writer" title="asyncio.loop.add_writer"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_writer()</span></code></a> 只接受套接字处理回调函数(如管道、文件描述符等都不支持)。</p></li>
<li><p>因为不支持管道,所以 <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.connect_read_pipe" title="asyncio.loop.connect_read_pipe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.connect_read_pipe()</span></code></a><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.connect_write_pipe" title="asyncio.loop.connect_write_pipe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.connect_write_pipe()</span></code></a> 方法没有实现。</p></li>
<li><p>不支持 <a class="reference internal" href="asyncio-subprocess.html#asyncio-subprocess"><span class="std std-ref">Subprocesses</span></a> ,也就是 <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_exec()</span></code></a><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_shell" title="asyncio.loop.subprocess_shell"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_shell()</span></code></a> 方法没有实现。</p></li>
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<p><a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> 有下列限制:</p>
<ul class="simple">
<li><p>不支持 <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_reader" title="asyncio.loop.add_reader"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_reader()</span></code></a><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_writer" title="asyncio.loop.add_writer"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_writer()</span></code></a> 方法。</p></li>
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<p>Windows上单调时钟的分辨率大约为 15.6 毫秒。最佳的分辨率是 0.5 毫秒。分辨率依赖于具体的硬件(<a class="reference external" href="https://zh.wikipedia.org/wiki/高精度事件计时器">HPET</a>和Windows的设置。</p>
<section id="subprocess-support-on-windows">
<span id="asyncio-windows-subprocess"></span><h3>Windows的子进程支持<a class="headerlink" href="#subprocess-support-on-windows" title="永久链接至标题"></a></h3>
<p>在 Windows 上,默认的事件循环 <a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> 支持子进程,而 <a class="reference internal" href="asyncio-eventloop.html#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorEventLoop</span></code></a> 则不支持。</p>
<p>也不支持 <a class="reference internal" href="asyncio-policy.html#asyncio.AbstractEventLoopPolicy.set_child_watcher" title="asyncio.AbstractEventLoopPolicy.set_child_watcher"><code class="xref py py-meth docutils literal notranslate"><span class="pre">policy.set_child_watcher()</span></code></a> 函数,<a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> 有不同的机制来监视子进程。</p>
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<h2>macOS<a class="headerlink" href="#macos" title="永久链接至标题"></a></h2>
<p>完整支持流行的macOS版本。</p>
<p class="rubric">macOS &lt;= 10.8</p>
<p>在 macOS 10.6, 10.7 和 10.8 上,默认的事件循环使用 <a class="reference internal" href="selectors.html#selectors.KqueueSelector" title="selectors.KqueueSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">selectors.KqueueSelector</span></code></a>,在这些版本上它并不支持字符设备。 可以手工配置 <a class="reference internal" href="asyncio-eventloop.html#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorEventLoop</span></code></a> 来使用 <a class="reference internal" href="selectors.html#selectors.SelectSelector" title="selectors.SelectSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectSelector</span></code></a><a class="reference internal" href="selectors.html#selectors.PollSelector" title="selectors.PollSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">PollSelector</span></code></a> 以在这些较老版本的 macOS 上支持字符设备。 例如:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="kn">import</span> <span class="nn">selectors</span>
<span class="n">selector</span> <span class="o">=</span> <span class="n">selectors</span><span class="o">.</span><span class="n">SelectSelector</span><span class="p">()</span>
<span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">SelectorEventLoop</span><span class="p">(</span><span class="n">selector</span><span class="p">)</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">set_event_loop</span><span class="p">(</span><span class="n">loop</span><span class="p">)</span>
</pre></div>
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