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><H1
><A
NAME="function.stream-select"
></A
>stream_select</H1
><DIV
CLASS="refnamediv"
><A
NAME="AEN73968"
></A
><P
> (PHP 4 >= 4.3.0)</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="AEN73971"
></A
><H2
>Description</H2
>int <B
CLASS="methodname"
>stream_select</B
> ( resource &read, resource &write, resource &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 opperation 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 <TT
CLASS="parameter"
><I
>read</I
></TT
> 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 <TT
CLASS="parameter"
><I
>write</I
></TT
> array will be
watched to see if a write will not block.
</P
><P
> The streams listed in the <TT
CLASS="parameter"
><I
>except</I
></TT
> array will be
watched for exceptions.
</P
><DIV
CLASS="warning"
><P
></P
><TABLE
CLASS="warning"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Aviso</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> On exit, the arrays are modified to indicate which stream resource
actually changed status.
</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
> Example:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>/* Prepare the read array */
$read = array($stream1, $stream2);
if (false === ($num_changed_streams = stream_select($read, $write = NULL, $except = NULL, 0))) {
/* Error handling */
else if ($num_changed_streams > 0) {
/* At least on one of the streams something interesting happened */
}</PRE
></TD
></TR
></TABLE
>
</P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Nota: </B
>
Due 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
><PRE
CLASS="php"
>stream_select($r, $w, $e = NULL, 0);</PRE
></TD
></TR
></TABLE
>
</P
></BLOCKQUOTE
></DIV
><P
> The <TT
CLASS="parameter"
><I
>tv_sec</I
></TT
> and <TT
CLASS="parameter"
><I
>tv_usec</I
></TT
>
together form the <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>timeout</I
></SPAN
> parameter. The
<SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>timeout</I
></SPAN
> is an upper bound on the amount of time
elapsed before <B
CLASS="function"
>stream_select()</B
> returns.
<TT
CLASS="parameter"
><I
>tv_sec</I
></TT
> may be zero , causing
<B
CLASS="function"
>stream_select()</B
> to return immediately. This is useful
for polling. If <TT
CLASS="parameter"
><I
>tv_sec</I
></TT
> is <TT
CLASS="constant"
><B
>NULL</B
></TT
> (no timeout),
<B
CLASS="function"
>stream_select()</B
> can block indefinitely.
</P
><P
> On success <B
CLASS="function"
>stream_select()</B
> returns the number of
stream resorces contained in the modified arrays, which may be zero if
the timeout expires before anything interesting happens. On error <TT
CLASS="constant"
><B
>FALSE</B
></TT
>
is returned.
</P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Nota: </B
>
Be sure to use the <TT
CLASS="literal"
>===</TT
> operator when checking for an
error. Since the <B
CLASS="function"
>stream_select()</B
> may return 0 the
comparison with <TT
CLASS="literal"
>==</TT
> would evaluate to <TT
CLASS="constant"
><B
>TRUE</B
></TT
>:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>if (false === stream_select($r, $w, $e = NULL, 0)) {
echo "stream_select() failed\n";
}</PRE
></TD
></TR
></TABLE
>
</P
></BLOCKQUOTE
></DIV
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Nota: </B
>
Be aware that some stream implementations need to be handled very
carefully. A few basic rules:
<P
></P
><UL
><LI
><P
> You should always try to use <B
CLASS="function"
>stream_select()</B
>
without timeout. Your program should have nothing to do if there is
no data available. Code that depends on timeouts is not usually
portable and difficult to debug.
</P
></LI
><LI
><P
> 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
></LI
></UL
>
</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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