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<section id="module-fcntl">
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<span id="fcntl-the-fcntl-and-ioctl-system-calls"></span><h1><a class="reference internal" href="#module-fcntl" title="fcntl: The fcntl() and ioctl() system calls. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">fcntl</span></code></a> —— 系统调用 <code class="docutils literal notranslate"><span class="pre">fcntl</span></code> 和 <code class="docutils literal notranslate"><span class="pre">ioctl</span></code><a class="headerlink" href="#module-fcntl" title="永久链接至标题">¶</a></h1>
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<p>本模块基于文件描述符来进行文件控制和 I/O 控制。它是 Unix 系统调用 <code class="xref c c-func docutils literal notranslate"><span class="pre">fcntl()</span></code> 和 <code class="xref c c-func docutils literal notranslate"><span class="pre">ioctl()</span></code> 的接口。关于这些调用的完整描述，请参阅 Unix 手册的 <em class="manpage"><a class="manpage reference external" href="https://manpages.debian.org/fcntl(2)">fcntl(2)</a></em> 和 <em class="manpage"><a class="manpage reference external" href="https://manpages.debian.org/ioctl(2)">ioctl(2)</a></em> 页面。</p>
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<p>本模块的所有函数都接受文件描述符 <em>fd</em> 作为第一个参数。可以是一个整数形式的文件描述符，比如 <code class="docutils literal notranslate"><span class="pre">sys.stdin.fileno()</span></code> 的返回结果，或为 <a class="reference internal" href="io.html#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">io.IOBase</span></code></a> 对象，比如 <code class="docutils literal notranslate"><span class="pre">sys.stdin</span></code> 提供一个 <a class="reference internal" href="io.html#io.IOBase.fileno" title="io.IOBase.fileno"><code class="xref py py-meth docutils literal notranslate"><span class="pre">fileno()</span></code></a>，可返回一个真正的文件描述符。</p>
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<div class="versionchanged">
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<p><span class="versionmodified changed">在 3.3 版更改: </span>本模块的操作以前触发的是 <a class="reference internal" href="exceptions.html#IOError" title="IOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IOError</span></code></a>，现在则会触发 <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a>。</p>
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</div>
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<div class="versionchanged">
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<p><span class="versionmodified changed">在 3.8 版更改: </span>fcntl 模块现在有了 <code class="docutils literal notranslate"><span class="pre">F_ADD_SEALS</span></code> 、<code class="docutils literal notranslate"><span class="pre">F_GET_SEALS</span></code> 和 <code class="docutils literal notranslate"><span class="pre">F_SEAL_*</span></code> 常量，用于文件描述符 <a class="reference internal" href="os.html#os.memfd_create" title="os.memfd_create"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.memfd_create()</span></code></a> 的封装。</p>
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</div>
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<p>这个模块定义了以下函数：</p>
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<dl class="function">
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<dt id="fcntl.fcntl">
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<code class="sig-prename descclassname">fcntl.</code><code class="sig-name descname">fcntl</code><span class="sig-paren">(</span><em class="sig-param">fd</em>, <em class="sig-param">cmd</em>, <em class="sig-param">arg=0</em><span class="sig-paren">)</span><a class="headerlink" href="#fcntl.fcntl" title="永久链接至目标">¶</a></dt>
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<dd><p>对文件描述符 <em>fd</em> 执行 <em>cmd</em> 操作（能够提供 <a class="reference internal" href="io.html#io.IOBase.fileno" title="io.IOBase.fileno"><code class="xref py py-meth docutils literal notranslate"><span class="pre">fileno()</span></code></a> 方法的文件对象也可以接受）。 <em>cmd</em> 可用的值与操作系统有关，在 <a class="reference internal" href="#module-fcntl" title="fcntl: The fcntl() and ioctl() system calls. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">fcntl</span></code></a> 模块中可作为常量使用，名称与相关 C 语言头文件中的一样。参数 <em>arg</em> 可以是整数或 <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> 对象。若为整数值，则本函数的返回值是 C 语言 <code class="xref c c-func docutils literal notranslate"><span class="pre">fcntl()</span></code> 调用的整数返回值。若为字节串，则其代表一个二进制结构，比如由 <a class="reference internal" href="struct.html#struct.pack" title="struct.pack"><code class="xref py py-func docutils literal notranslate"><span class="pre">struct.pack()</span></code></a> 创建的数据。该二进制数据将被复制到一个缓冲区，缓冲区地址传给 C 调用 <code class="xref c c-func docutils literal notranslate"><span class="pre">fcntl()</span></code>。调用成功后的返回值位于缓冲区内，转换为一个 <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> 对象。返回的对象长度将与 <em>arg</em> 参数的长度相同。上限为 1024 字节。如果操作系统在缓冲区中返回的信息大于 1024 字节，很可能导致内存段冲突，或更为不易察觉的数据错误。</p>
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<p>如果 <code class="xref c c-func docutils literal notranslate"><span class="pre">fcntl()</span></code> 调用失败，会触发 <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a> 。</p>
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<p class="audit-hook">引发一个 <a class="reference internal" href="sys.html#auditing"><span class="std std-ref">审计事件</span></a> <code class="docutils literal notranslate"><span class="pre">fcntl.fcntl</span></code> 并附带参数 <code class="docutils literal notranslate"><span class="pre">fd</span></code>, <code class="docutils literal notranslate"><span class="pre">cmd</span></code>, <code class="docutils literal notranslate"><span class="pre">arg</span></code>。</p>
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</dd></dl>
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<dl class="function">
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<dt id="fcntl.ioctl">
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<code class="sig-prename descclassname">fcntl.</code><code class="sig-name descname">ioctl</code><span class="sig-paren">(</span><em class="sig-param">fd</em>, <em class="sig-param">request</em>, <em class="sig-param">arg=0</em>, <em class="sig-param">mutate_flag=True</em><span class="sig-paren">)</span><a class="headerlink" href="#fcntl.ioctl" title="永久链接至目标">¶</a></dt>
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<dd><p>本函数与 <a class="reference internal" href="#fcntl.fcntl" title="fcntl.fcntl"><code class="xref py py-func docutils literal notranslate"><span class="pre">fcntl()</span></code></a> 函数相同，只是参数的处理更加复杂。</p>
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<p><em>request</em> 参数的上限是 32位。<a class="reference internal" href="termios.html#module-termios" title="termios: POSIX style tty control. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">termios</span></code></a> 模块中包含了可用作 <em>request</em> 参数其他常量，名称与相关 C 头文件中定义的相同。</p>
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<p>参数 <em>arg</em> 可为整数、支持只读缓冲区接口的对象（如 <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> ）或支持读写缓冲区接口的对象（如 <a class="reference internal" href="stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytearray</span></code></a> ）。</p>
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<p>除了最后一种情况，其他情况下的行为都与 <a class="reference internal" href="#fcntl.fcntl" title="fcntl.fcntl"><code class="xref py py-func docutils literal notranslate"><span class="pre">fcntl()</span></code></a> 函数一样。</p>
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<p>如果传入的是个可变缓冲区，那么行为就由 <em>mutate_flag</em> 参数决定。</p>
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<p>如果 <em>mutate_flag</em> 为 False，缓冲区的可变性将被忽略，行为与只读缓冲区一样，只是没有了上述 1024 字节的上限——只要传入的缓冲区能容纳操作系统放入的数据即可。</p>
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<p>如果 <em>mutate_flag</em> 为 True（默认值），那么缓冲区（实际上）会传给底层的 系统调用 <a class="reference internal" href="#fcntl.ioctl" title="fcntl.ioctl"><code class="xref py py-func docutils literal notranslate"><span class="pre">ioctl()</span></code></a> ，其返回代码则会回传给调用它的 Python，而缓冲区的新数据则反映了 <a class="reference internal" href="#fcntl.ioctl" title="fcntl.ioctl"><code class="xref py py-func docutils literal notranslate"><span class="pre">ioctl()</span></code></a> 的运行结果。这里做了一点简化，因为若是给出的缓冲区少于 1024 字节，首先会被复制到一个 1024 字节长的静态缓冲区再传给 <a class="reference internal" href="#fcntl.ioctl" title="fcntl.ioctl"><code class="xref py py-func docutils literal notranslate"><span class="pre">ioctl()</span></code></a> ，然后把结果复制回给出的缓冲区去。</p>
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<p>如果 <code class="xref c c-func docutils literal notranslate"><span class="pre">ioctl()</span></code> 调用失败，则会触发 <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a> 异常。</p>
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<p>举个例子：</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">array</span><span class="o">,</span> <span class="nn">fcntl</span><span class="o">,</span> <span class="nn">struct</span><span class="o">,</span> <span class="nn">termios</span><span class="o">,</span> <span class="nn">os</span>
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||
<span class="gp">>>> </span><span class="n">os</span><span class="o">.</span><span class="n">getpgrp</span><span class="p">()</span>
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<span class="go">13341</span>
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<span class="gp">>>> </span><span class="n">struct</span><span class="o">.</span><span class="n">unpack</span><span class="p">(</span><span class="s1">'h'</span><span class="p">,</span> <span class="n">fcntl</span><span class="o">.</span><span class="n">ioctl</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">termios</span><span class="o">.</span><span class="n">TIOCGPGRP</span><span class="p">,</span> <span class="s2">" "</span><span class="p">))[</span><span class="mi">0</span><span class="p">]</span>
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<span class="go">13341</span>
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<span class="gp">>>> </span><span class="n">buf</span> <span class="o">=</span> <span class="n">array</span><span class="o">.</span><span class="n">array</span><span class="p">(</span><span class="s1">'h'</span><span class="p">,</span> <span class="p">[</span><span class="mi">0</span><span class="p">])</span>
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<span class="gp">>>> </span><span class="n">fcntl</span><span class="o">.</span><span class="n">ioctl</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">termios</span><span class="o">.</span><span class="n">TIOCGPGRP</span><span class="p">,</span> <span class="n">buf</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
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<span class="go">0</span>
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<span class="gp">>>> </span><span class="n">buf</span>
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<span class="go">array('h', [13341])</span>
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</pre></div>
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</div>
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<p class="audit-hook">引发一个 <a class="reference internal" href="sys.html#auditing"><span class="std std-ref">审计事件</span></a> <code class="docutils literal notranslate"><span class="pre">fcntl.ioctl</span></code> 并附带参数 <code class="docutils literal notranslate"><span class="pre">fd</span></code>, <code class="docutils literal notranslate"><span class="pre">request</span></code>, <code class="docutils literal notranslate"><span class="pre">arg</span></code>。</p>
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</dd></dl>
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<dl class="function">
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<dt id="fcntl.flock">
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<code class="sig-prename descclassname">fcntl.</code><code class="sig-name descname">flock</code><span class="sig-paren">(</span><em class="sig-param">fd</em>, <em class="sig-param">operation</em><span class="sig-paren">)</span><a class="headerlink" href="#fcntl.flock" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>在文件描述符 <em>fd</em> 上执行加锁操作 <em>operation</em> (也接受能提供 <a class="reference internal" href="io.html#io.IOBase.fileno" title="io.IOBase.fileno"><code class="xref py py-meth docutils literal notranslate"><span class="pre">fileno()</span></code></a> 方法的文件对象)。 详见 Unix 手册 <em class="manpage"><a class="manpage reference external" href="https://manpages.debian.org/flock(2)">flock(2)</a></em>。 (在某些系统中，此函数是用 <code class="xref c c-func docutils literal notranslate"><span class="pre">fcntl()</span></code> 模拟出来的。)</p>
|
||
<p>如果 <code class="xref c c-func docutils literal notranslate"><span class="pre">flock()</span></code> 调用失败，就会触发 <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a> 异常。</p>
|
||
<p class="audit-hook">引发一个 <a class="reference internal" href="sys.html#auditing"><span class="std std-ref">审计事件</span></a> <code class="docutils literal notranslate"><span class="pre">fcntl.flock</span></code> 并附带参数 <code class="docutils literal notranslate"><span class="pre">fd</span></code>, <code class="docutils literal notranslate"><span class="pre">operation</span></code>。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="fcntl.lockf">
|
||
<code class="sig-prename descclassname">fcntl.</code><code class="sig-name descname">lockf</code><span class="sig-paren">(</span><em class="sig-param">fd</em>, <em class="sig-param">cmd</em>, <em class="sig-param">len=0</em>, <em class="sig-param">start=0</em>, <em class="sig-param">whence=0</em><span class="sig-paren">)</span><a class="headerlink" href="#fcntl.lockf" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>本质上是对 <a class="reference internal" href="#fcntl.fcntl" title="fcntl.fcntl"><code class="xref py py-func docutils literal notranslate"><span class="pre">fcntl()</span></code></a> 加锁调用的封装。<em>fd</em> 是要加解锁的文件描述符（也接受能提供 <a class="reference internal" href="io.html#io.IOBase.fileno" title="io.IOBase.fileno"><code class="xref py py-meth docutils literal notranslate"><span class="pre">fileno()</span></code></a> 方法的文件对象），<em>cmd</em> 是以下值之一：</p>
|
||
<ul class="simple">
|
||
<li><p><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCK_UN</span></code> ——解锁</p></li>
|
||
<li><p><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCK_SH</span></code> —— 获取一个共享锁</p></li>
|
||
<li><p><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCK_EX</span></code> —— 获取一个独占锁</p></li>
|
||
</ul>
|
||
<p>如果 <em>cmd</em> 为 <code class="xref py py-const docutils literal notranslate"><span class="pre">LOCK_SH</span></code> 或 <code class="xref py py-const docutils literal notranslate"><span class="pre">LOCK_EX</span></code>，则还可以与 <code class="xref py py-const docutils literal notranslate"><span class="pre">LOCK_NB</span></code> 进行按位或运算，以避免在获取锁时出现阻塞。 如果用了 <code class="xref py py-const docutils literal notranslate"><span class="pre">LOCK_NB</span></code>，无法获取锁时将触发 <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a>，此异常的 <em>errno</em> 属性将被设为 <code class="xref py py-const docutils literal notranslate"><span class="pre">EACCES</span></code> 或 <code class="xref py py-const docutils literal notranslate"><span class="pre">EAGAIN</span></code> (视操作系统而定；为了保证可移植性，请检查这两个值)。 至少在某些系统上，只有当文件描述符指向需要写入而打开的文件时，才可以使用 <code class="xref py py-const docutils literal notranslate"><span class="pre">LOCK_EX</span></code>。</p>
|
||
<p><em>len</em> 是要锁定的字节数，<em>start</em> 是自 <em>whence</em> 开始锁定的字节偏移量，<em>whence</em> 与 <a class="reference internal" href="io.html#io.IOBase.seek" title="io.IOBase.seek"><code class="xref py py-func docutils literal notranslate"><span class="pre">io.IOBase.seek()</span></code></a> 的定义一样。</p>
|
||
<ul class="simple">
|
||
<li><p><code class="xref py py-const docutils literal notranslate"><span class="pre">0</span></code> —— 自文件起始位置（<a class="reference internal" href="os.html#os.SEEK_SET" title="os.SEEK_SET"><code class="xref py py-data docutils literal notranslate"><span class="pre">os.SEEK_SET</span></code></a>）。</p></li>
|
||
<li><p><code class="xref py py-const docutils literal notranslate"><span class="pre">1</span></code> —— 自缓冲区当前位置（ <a class="reference internal" href="os.html#os.SEEK_CUR" title="os.SEEK_CUR"><code class="xref py py-data docutils literal notranslate"><span class="pre">os.SEEK_CUR</span></code></a> ）</p></li>
|
||
<li><p><code class="xref py py-const docutils literal notranslate"><span class="pre">2</span></code>—— 自文件末尾（<a class="reference internal" href="os.html#os.SEEK_END" title="os.SEEK_END"><code class="xref py py-data docutils literal notranslate"><span class="pre">os.SEEK_END</span></code></a>)</p></li>
|
||
</ul>
|
||
<p><em>start</em> 的默认值为 0，表示从文件起始位置开始。<em>len</em> 的默认值是 0，表示加锁至文件末尾。 <em>whence</em> 的默认值也是 0。</p>
|
||
<p class="audit-hook">引发一个 <a class="reference internal" href="sys.html#auditing"><span class="std std-ref">审计事件</span></a> <code class="docutils literal notranslate"><span class="pre">fcntl.lockf</span></code> 并附带参数 <code class="docutils literal notranslate"><span class="pre">fd</span></code>, <code class="docutils literal notranslate"><span class="pre">cmd</span></code>, <code class="docutils literal notranslate"><span class="pre">len</span></code>, <code class="docutils literal notranslate"><span class="pre">start</span></code>, <code class="docutils literal notranslate"><span class="pre">whence</span></code>。</p>
|
||
</dd></dl>
|
||
|
||
<p>示例（都是运行于符合 SVR4 的系统）：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">struct</span><span class="o">,</span> <span class="nn">fcntl</span><span class="o">,</span> <span class="nn">os</span>
|
||
|
||
<span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="o">...</span><span class="p">)</span>
|
||
<span class="n">rv</span> <span class="o">=</span> <span class="n">fcntl</span><span class="o">.</span><span class="n">fcntl</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">fcntl</span><span class="o">.</span><span class="n">F_SETFL</span><span class="p">,</span> <span class="n">os</span><span class="o">.</span><span class="n">O_NDELAY</span><span class="p">)</span>
|
||
|
||
<span class="n">lockdata</span> <span class="o">=</span> <span class="n">struct</span><span class="o">.</span><span class="n">pack</span><span class="p">(</span><span class="s1">'hhllhh'</span><span class="p">,</span> <span class="n">fcntl</span><span class="o">.</span><span class="n">F_WRLCK</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span>
|
||
<span class="n">rv</span> <span class="o">=</span> <span class="n">fcntl</span><span class="o">.</span><span class="n">fcntl</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">fcntl</span><span class="o">.</span><span class="n">F_SETLKW</span><span class="p">,</span> <span class="n">lockdata</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>注意，在第一个例子中，返回值变量 <em>rv</em> 将存有整数；在第二个例子中，该变量中将存有一个 <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> 对象。<em>lockdata</em> 变量的结构布局视系统而定——因此采用 <a class="reference internal" href="#fcntl.flock" title="fcntl.flock"><code class="xref py py-func docutils literal notranslate"><span class="pre">flock()</span></code></a> 调用可能会更好。</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">参见</p>
|
||
<dl class="simple">
|
||
<dt>模块 <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a></dt><dd><p>如果 <a class="reference internal" href="os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> 模块中存在加锁标志 <a class="reference internal" href="os.html#os.O_SHLOCK" title="os.O_SHLOCK"><code class="xref py py-data docutils literal notranslate"><span class="pre">O_SHLOCK</span></code></a> 和 <a class="reference internal" href="os.html#os.O_EXLOCK" title="os.O_EXLOCK"><code class="xref py py-data docutils literal notranslate"><span class="pre">O_EXLOCK</span></code></a> （仅在BSD上），那么 <a class="reference internal" href="os.html#os.open" title="os.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.open()</span></code></a> 函数提供了 <a class="reference internal" href="#fcntl.lockf" title="fcntl.lockf"><code class="xref py py-func docutils literal notranslate"><span class="pre">lockf()</span></code></a> 和 <a class="reference internal" href="#fcntl.flock" title="fcntl.flock"><code class="xref py py-func docutils literal notranslate"><span class="pre">flock()</span></code></a> 函数的替代方案。</p>
|
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</dd>
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