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><H1
><A
NAME="function.stream-select"
></A
>stream_select</H1
><DIV
CLASS="refnamediv"
><A
NAME="AEN223445"
></A
><P
> (PHP 4 >= 4.3.0, PHP 5)</P
>stream_select -- Runs the equivalent of the select() system call on the given
arrays of streams with a timeout specified by tv_sec and tv_usec </DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN223448"
></A
><H2
>Description</H2
>int <B
CLASS="methodname"
>stream_select</B
> ( array &read, array &write, array &except, int tv_sec [, int tv_usec] )<BR
></BR
><P
> The <B
CLASS="function"
>stream_select()</B
> function accepts arrays of streams and
waits for them to change status. Its operation is equivalent to that of
the <A
HREF="function.socket-select.html"
><B
CLASS="function"
>socket_select()</B
></A
> function except in that it acts on streams.
</P
><P
> The streams listed in the <CODE
CLASS="parameter"
>read</CODE
> array will be watched to
see if characters become available for reading (more precisely, to see if
a read will not block - in particular, a stream resource is also ready on
end-of-file, in which case an <A
HREF="function.fread.html"
><B
CLASS="function"
>fread()</B
></A
> will return
a zero length string).
</P
><P
> The streams listed in the <CODE
CLASS="parameter"
>write</CODE
> array will be
watched to see if a write will not block.
</P
><P
> The streams listed in the <CODE
CLASS="parameter"
>except</CODE
> array will be
watched for high priority exceptional ("out-of-band") data arriving.
</P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>注意: </B
>
When <B
CLASS="function"
>stream_select()</B
> returns, the arrays
<CODE
CLASS="parameter"
>read</CODE
>, <CODE
CLASS="parameter"
>write</CODE
> and
<CODE
CLASS="parameter"
>except</CODE
> are modified to indicate which stream
resource(s) actually changed status.
</P
></BLOCKQUOTE
></DIV
><P
> The <CODE
CLASS="parameter"
>tv_sec</CODE
> and <CODE
CLASS="parameter"
>tv_usec</CODE
>
together form the <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>timeout</I
></SPAN
> parameter,
<CODE
CLASS="parameter"
>tv_sec</CODE
> specifies the number of seconds while
<CODE
CLASS="parameter"
>tv_usec</CODE
> the number of microseconds.
The <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>timeout</I
></SPAN
> is an upper bound on the amount of time
that <B
CLASS="function"
>stream_select()</B
> will wait before it returns.
If <CODE
CLASS="parameter"
>tv_sec</CODE
> and <CODE
CLASS="parameter"
>tv_usec</CODE
> are
both set to <TT
CLASS="literal"
>0</TT
>, <B
CLASS="function"
>stream_select()</B
> will
not wait for data - instead it will return immediately, indicating the
current status of the streams.
If <CODE
CLASS="parameter"
>tv_sec</CODE
> is <TT
CLASS="constant"
><B
>NULL</B
></TT
> <B
CLASS="function"
>stream_select()</B
>
can block indefinitely, returning only when an event on one of the
watched streams occurs (or if a signal interrupts the system call).
</P
><P
> On success <B
CLASS="function"
>stream_select()</B
> returns the number of
stream resources contained in the modified arrays, which may be zero if
the timeout expires before anything interesting happens. On error <TT
CLASS="constant"
><B
>FALSE</B
></TT
>
is returned and a warning raised (this can happen if the system call is
interrupted by an incoming signal).
</P
><DIV
CLASS="warning"
><P
></P
><TABLE
CLASS="warning"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>警告</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> Using a timeout value of <TT
CLASS="literal"
>0</TT
> allows you to
instantaneously poll the status of the streams, however, it is NOT a
good idea to use a <TT
CLASS="literal"
>0</TT
> timeout value in a loop as it
will cause your script to consume too much CPU time.
</P
><P
> It is much better to specify a timeout value of a few seconds, although
if you need to be checking and running other code concurrently, using a
timeout value of at least <TT
CLASS="literal"
>200000</TT
> microseconds will
help reduce the CPU usage of your script.
</P
><P
> Remember that the timeout value is the
maximum time that will elapse; <B
CLASS="function"
>stream_select()</B
> will
return as soon as the requested streams are ready for use.
</P
></TD
></TR
></TABLE
></DIV
><P
> You do not need to pass every array to
<B
CLASS="function"
>stream_select()</B
>. You can leave it out and use an
empty array or <TT
CLASS="constant"
><B
>NULL</B
></TT
> instead. Also do not forget that those arrays are
passed <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>by reference</I
></SPAN
> and will be modified after
<B
CLASS="function"
>stream_select()</B
> returns.
</P
><P
> This example checks to see if data has arrived for reading on either
<CODE
CLASS="parameter"
>$stream1</CODE
> or <CODE
CLASS="parameter"
>$stream2</CODE
>.
Since the timeout value is <TT
CLASS="literal"
>0</TT
> it will return
immediately:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#FF8000">/* Prepare the read array */<br /></font><font color="#0000BB">$read </font><font color="#007700">= array(</font><font color="#0000BB">$stream1</font><font color="#007700">, </font><font color="#0000BB">$stream2</font><font color="#007700">);<br /></font><font color="#0000BB">$write </font><font color="#007700">= </font><font color="#0000BB">NULL</font><font color="#007700">;<br /></font><font color="#0000BB">$except </font><font color="#007700">= </font><font color="#0000BB">NULL</font><font color="#007700">;<br />if (</font><font color="#0000BB">false </font><font color="#007700">=== (</font><font color="#0000BB">$num_changed_streams </font><font color="#007700">= </font><font color="#0000BB">stream_select</font><font color="#007700">(</font><font color="#0000BB">$read</font><font color="#007700">, </font><font color="#0000BB">$write</font><font color="#007700">, </font><font color="#0000BB">$except</font><font color="#007700">, </font><font color="#0000BB">0</font><font color="#007700">))) {<br /> </font><font color="#FF8000">/* Error handling */<br /></font><font color="#007700">} elseif (</font><font color="#0000BB">$num_changed_streams </font><font color="#007700">> </font><font color="#0000BB">0</font><font color="#007700">) {<br /> </font><font color="#FF8000">/* At least on one of the streams something interesting happened */<br /></font><font color="#007700">}<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
>
</P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>注意: </B
>
Due to a limitation in the current Zend Engine it is not possible to pass a
constant modifier like <TT
CLASS="constant"
><B
>NULL</B
></TT
> directly as a parameter to a function
which expects this parameter to be passed by reference. Instead use a
temporary variable or an expression with the leftmost member being a
temporary variable:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br />$e </font><font color="#007700">= </font><font color="#0000BB">NULL</font><font color="#007700">;<br /></font><font color="#0000BB">stream_select</font><font color="#007700">(</font><font color="#0000BB">$r</font><font color="#007700">, </font><font color="#0000BB">$w</font><font color="#007700">, </font><font color="#0000BB">$e</font><font color="#007700">, </font><font color="#0000BB">0</font><font color="#007700">);<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
>
</P
></BLOCKQUOTE
></DIV
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>注意: </B
>
Be sure to use the <TT
CLASS="literal"
>===</TT
> operator when checking for an
error. Since the <B
CLASS="function"
>stream_select()</B
> may return 0 the
comparison with <TT
CLASS="literal"
>==</TT
> would evaluate to <TT
CLASS="constant"
><B
>TRUE</B
></TT
>:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br />$e </font><font color="#007700">= </font><font color="#0000BB">NULL</font><font color="#007700">;<br />if (</font><font color="#0000BB">false </font><font color="#007700">=== </font><font color="#0000BB">stream_select</font><font color="#007700">(</font><font color="#0000BB">$r</font><font color="#007700">, </font><font color="#0000BB">$w</font><font color="#007700">, </font><font color="#0000BB">$e</font><font color="#007700">, </font><font color="#0000BB">0</font><font color="#007700">)) {<br /> echo </font><font color="#DD0000">"stream_select() failed\n"</font><font color="#007700">;<br />}<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
>
</P
></BLOCKQUOTE
></DIV
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>注意: </B
>
If you read/write to a stream returned in the arrays be aware that
they do not necessarily read/write the full amount of data you have
requested. Be prepared to even only be able to read/write a single
byte.
</P
></BLOCKQUOTE
></DIV
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>注意: </B
>
Windows compatibility: <B
CLASS="function"
>stream_select()</B
> used on a
pipe returned from <A
HREF="function.proc-open.html"
><B
CLASS="function"
>proc_open()</B
></A
> may cause data loss
under Windows 98.
</P
><P
> Use of <B
CLASS="function"
>stream_select()</B
> on
file descriptors returned by <A
HREF="function.proc-open.html"
><B
CLASS="function"
>proc_open()</B
></A
> will fail
and return <TT
CLASS="constant"
><B
>FALSE</B
></TT
> under Windows.
</P
></BLOCKQUOTE
></DIV
><P
> See also
<A
HREF="function.stream-set-blocking.html"
><B
CLASS="function"
>stream_set_blocking()</B
></A
>.
</P
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