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264 lines
14 KiB
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>Runs the equivalent of the select() system call on the given
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arrays of streams with a timeout specified by tv_sec and tv_usec</title>
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</head>
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<body class="docs"></div>
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<div id="layout">
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<div id="layout-content"><div id="function.stream-select" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">stream_select</h1>
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<p class="verinfo">(PHP 4 >= 4.3.0, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">stream_select</span> — <span class="dc-title">Runs the equivalent of the select() system call on the given
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arrays of streams with a timeout specified by tv_sec and tv_usec </span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.stream-select-description">
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<h3 class="title">说明</h3>
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<div class="methodsynopsis dc-description">
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<span class="methodname"><strong>stream_select</strong></span>
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( <span class="methodparam"><span class="type">array</span> <code class="parameter reference">&$read</code></span>
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, <span class="methodparam"><span class="type">array</span> <code class="parameter reference">&$write</code></span>
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, <span class="methodparam"><span class="type">array</span> <code class="parameter reference">&$except</code></span>
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, <span class="methodparam"><span class="type">int</span> <code class="parameter">$tv_sec</code></span>
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[, <span class="methodparam"><span class="type">int</span> <code class="parameter">$tv_usec</code><span class="initializer"> = 0</span></span>
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] ) : <span class="type">int</span></div>
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<p class="para rdfs-comment">
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The <span class="function"><strong>stream_select()</strong></span> function accepts arrays of streams and
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waits for them to change status. Its operation is equivalent to that of
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the <span class="function"><a href="socket_select.html" class="function">socket_select()</a></span> function except in that it acts on streams.
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</p>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.stream-select-parameters">
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<h3 class="title">参数</h3>
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<p class="para">
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<dl>
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<dt>
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<code class="parameter">read</code></dt>
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<dd>
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<p class="para">
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The streams listed in the <code class="parameter">read</code> array will be watched to
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see if characters become available for reading (more precisely, to see if
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a read will not block - in particular, a stream resource is also ready on
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end-of-file, in which case an <span class="function"><a href="fread.html" class="function">fread()</a></span> will return
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a zero length string).
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</p>
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</dd>
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<dt>
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<code class="parameter">write</code></dt>
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<dd>
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<p class="para">
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The streams listed in the <code class="parameter">write</code> array will be
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watched to see if a write will not block.
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</p>
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</dd>
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<dt>
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<code class="parameter">except</code></dt>
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<dd>
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<p class="para">
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The streams listed in the <code class="parameter">except</code> array will be
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watched for high priority exceptional ("out-of-band") data arriving.
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</p>
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<blockquote class="note"><p><strong class="note">Note</strong>:
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<p class="para">
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When <span class="function"><strong>stream_select()</strong></span> returns, the arrays
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<code class="parameter">read</code>, <code class="parameter">write</code> and
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<code class="parameter">except</code> are modified to indicate which stream
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resource(s) actually changed status.
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</p>
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</p></blockquote>
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<span class="simpara">
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You do not need to pass every array to
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<span class="function"><strong>stream_select()</strong></span>. You can leave it out and use an
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empty array or <strong><code>NULL</code></strong> instead. Also do not forget that those arrays are
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passed <em class="emphasis">by reference</em> and will be modified after
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<span class="function"><strong>stream_select()</strong></span> returns.
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</span>
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</dd>
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<dt>
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<code class="parameter">tv_sec</code></dt>
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<dd>
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<p class="para">
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The <code class="parameter">tv_sec</code> and <code class="parameter">tv_usec</code>
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together form the <em class="emphasis">timeout</em> parameter,
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<code class="parameter">tv_sec</code> specifies the number of seconds while
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<code class="parameter">tv_usec</code> the number of microseconds.
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The <code class="parameter">timeout</code> is an upper bound on the amount of time
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that <span class="function"><strong>stream_select()</strong></span> will wait before it returns.
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If <code class="parameter">tv_sec</code> and <code class="parameter">tv_usec</code> are
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both set to <em>0</em>, <span class="function"><strong>stream_select()</strong></span> will
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not wait for data - instead it will return immediately, indicating the
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current status of the streams.
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</p>
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<p class="para">
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If <code class="parameter">tv_sec</code> is <strong><code>NULL</code></strong> <span class="function"><strong>stream_select()</strong></span>
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can block indefinitely, returning only when an event on one of the
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watched streams occurs (or if a signal interrupts the system call).
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</p>
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<div class="warning"><strong class="warning">Warning</strong>
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<p class="para">
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Using a timeout value of <em>0</em> allows you to
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instantaneously poll the status of the streams, however, it is NOT a
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good idea to use a <em>0</em> timeout value in a loop as it
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will cause your script to consume too much CPU time.
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</p>
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<p class="para">
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It is much better to specify a timeout value of a few seconds, although
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if you need to be checking and running other code concurrently, using a
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timeout value of at least <em>200000</em> microseconds will
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help reduce the CPU usage of your script.
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</p>
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<p class="para">
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Remember that the timeout value is the maximum time that will elapse;
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<span class="function"><strong>stream_select()</strong></span> will return as soon as the
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requested streams are ready for use.
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</p>
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</div>
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</dd>
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<dt>
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<code class="parameter">tv_usec</code></dt>
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<dd>
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<p class="para">
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See <code class="parameter">tv_sec</code> description.
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</p>
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</dd>
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</dl>
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</p>
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</div>
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<div class="refsect1 returnvalues" id="refsect1-function.stream-select-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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On success <span class="function"><strong>stream_select()</strong></span> returns the number of
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stream resources contained in the modified arrays, which may be zero if
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the timeout expires before anything interesting happens. On error <strong><code>FALSE</code></strong>
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is returned and a warning raised (this can happen if the system call is
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interrupted by an incoming signal).
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</p>
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</div>
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<div class="refsect1 examples" id="refsect1-function.stream-select-examples">
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<h3 class="title">范例</h3>
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<p class="para">
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<div class="example" id="example-4833">
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<p><strong>Example #1 <span class="function"><strong>stream_select()</strong></span> Example</strong></p>
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<div class="example-contents"><p>
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This example checks to see if data has arrived for reading on either
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<code class="parameter">$stream1</code> or <code class="parameter">$stream2</code>.
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Since the timeout value is <em>0</em> it will return
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immediately:
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</p></div>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">/* Prepare the read array */<br /></span><span style="color: #0000BB">$read </span><span style="color: #007700">= array(</span><span style="color: #0000BB">$stream1</span><span style="color: #007700">, </span><span style="color: #0000BB">$stream2</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$write </span><span style="color: #007700">= </span><span style="color: #0000BB">NULL</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$except </span><span style="color: #007700">= </span><span style="color: #0000BB">NULL</span><span style="color: #007700">;<br />if (</span><span style="color: #0000BB">false </span><span style="color: #007700">=== (</span><span style="color: #0000BB">$num_changed_streams </span><span style="color: #007700">= </span><span style="color: #0000BB">stream_select</span><span style="color: #007700">(</span><span style="color: #0000BB">$read</span><span style="color: #007700">, </span><span style="color: #0000BB">$write</span><span style="color: #007700">, </span><span style="color: #0000BB">$except</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">))) {<br /> </span><span style="color: #FF8000">/* Error handling */<br /></span><span style="color: #007700">} elseif (</span><span style="color: #0000BB">$num_changed_streams </span><span style="color: #007700">> </span><span style="color: #0000BB">0</span><span style="color: #007700">) {<br /> </span><span style="color: #FF8000">/* At least on one of the streams something interesting happened */<br /></span><span style="color: #007700">}<br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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</div>
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</p>
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</div>
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<div class="refsect1 notes" id="refsect1-function.stream-select-notes">
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<h3 class="title">注释</h3>
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<blockquote class="note"><p><strong class="note">Note</strong>:
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<p class="para">
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Due to a limitation in the current Zend Engine it is not possible to pass a
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constant modifier like <strong><code>NULL</code></strong> directly as a parameter to a function
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which expects this parameter to be passed by reference. Instead use a
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temporary variable or an expression with the leftmost member being a
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temporary variable:
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br />$e </span><span style="color: #007700">= </span><span style="color: #0000BB">NULL</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">stream_select</span><span style="color: #007700">(</span><span style="color: #0000BB">$r</span><span style="color: #007700">, </span><span style="color: #0000BB">$w</span><span style="color: #007700">, </span><span style="color: #0000BB">$e</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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</p>
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</p></blockquote>
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<blockquote class="note"><p><strong class="note">Note</strong>:
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<p class="para">
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Be sure to use the <em>===</em> operator when checking for an
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error. Since the <span class="function"><strong>stream_select()</strong></span> may return 0 the
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comparison with <em>==</em> would evaluate to <strong><code>TRUE</code></strong>:
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br />$e </span><span style="color: #007700">= </span><span style="color: #0000BB">NULL</span><span style="color: #007700">;<br />if (</span><span style="color: #0000BB">false </span><span style="color: #007700">=== </span><span style="color: #0000BB">stream_select</span><span style="color: #007700">(</span><span style="color: #0000BB">$r</span><span style="color: #007700">, </span><span style="color: #0000BB">$w</span><span style="color: #007700">, </span><span style="color: #0000BB">$e</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">)) {<br /> echo </span><span style="color: #DD0000">"stream_select() failed\n"</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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</p>
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</p></blockquote>
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<blockquote class="note"><p><strong class="note">Note</strong>:
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<p class="para">
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If you read/write to a stream returned in the arrays be aware that
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they do not necessarily read/write the full amount of data you have
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requested. Be prepared to even only be able to read/write a single
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byte.
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</p>
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</p></blockquote>
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<blockquote class="note"><p><strong class="note">Note</strong>:
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<p class="para">
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Some streams (like <em>zlib</em>) cannot be selected by this
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function.
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</p>
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</p></blockquote>
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<blockquote class="note"><p><strong class="note">Note</strong>:
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<p class="para">
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Windows compatibility: <span class="function"><strong>stream_select()</strong></span> used on a
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pipe returned from <span class="function"><a href="proc_open.html" class="function">proc_open()</a></span> may cause data loss
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under Windows 98.
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</p>
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<p class="para">
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Use of <span class="function"><strong>stream_select()</strong></span> on
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file descriptors returned by <span class="function"><a href="proc_open.html" class="function">proc_open()</a></span> will fail
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and return <strong><code>FALSE</code></strong> under Windows.
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</p>
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</p></blockquote>
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</div>
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<div class="refsect1 seealso" id="refsect1-function.stream-select-seealso">
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<h3 class="title">参见</h3>
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<ul class="simplelist">
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<li class="member"><span class="function"><a href="stream_set_blocking.html" class="function" rel="rdfs-seeAlso">stream_set_blocking()</a> - 为资源流设置阻塞或者阻塞模式</span></li>
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</ul>
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</div>
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</div></div></div></body></html> |