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><H1
><A
NAME="function.socket-select"
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>socket_select</H1
><DIV
CLASS="refnamediv"
><A
NAME="AEN87866"
></A
><P
>    (PHP 4 &#62;= 4.1.0)</P
>socket_select&nbsp;--&nbsp;Runs the select() system call on the given arrays of sockets with a timeout specified by tv_sec and tv_usec </DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN87869"
></A
><H2
>Description</H2
>int <B
CLASS="methodname"
>socket_select</B
> ( resource &#38;read, resource &#38;write, resource &#38;except, int tv_sec [, int tv_usec])<BR
></BR
><DIV
CLASS="warning"
><P
></P
><TABLE
CLASS="warning"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Warning</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
>This function is
<SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>EXPERIMENTAL</I
></SPAN
>. The behaviour of this function, the
name of this function, and anything else documented about this
function may change without notice in a future release of PHP. 
Use this function at your own risk.</P
></TD
></TR
></TABLE
></DIV
><P
>&#13;     The <B
CLASS="function"
>socket_select()</B
> accepts arrays of sockets and
     waits for them to change status. Those coming with BSD sockets background
     will recognize that those socket resource arrays are in fact the
     so-called file descriptor sets. Three independent arrays of socket
     resources are watched.
    </P
><P
>&#13;     The sockets 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 socket resource is also ready on
     end-of-file, in which case a <A
HREF="function.socket-read.html"
><B
CLASS="function"
>socket_read()</B
></A
> will return
     a zero length string).
    </P
><P
>&#13;     The sockets listed in the <TT
CLASS="parameter"
><I
>write</I
></TT
> array will be
     watched  to  see if a write will not block.
    </P
><P
>&#13;     The sockets 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
>Warning</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
>&#13;      On exit, the arrays are modified to indicate which socket resource
      actually changed status.
     </P
></TD
></TR
></TABLE
></DIV
><P
>&#13;     You do not need to pass every array to
     <B
CLASS="function"
>socket_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"
>socket_select()</B
> returns.
    </P
><P
>&#13;     Example:
     <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>/* Prepare the read array */
$read = array($socket1, $socket2);

if (false === ($num_changed_sockets = socket_select($read, $write = NULL, $except = NULL, 0))) {
    /* Error handling */
else if ($num_changed_sockets &#62; 0) {
    /* At least at one of the sockets something interesting happened */
}</PRE
></TD
></TR
></TABLE
>
    </P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </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"
>socket_select($r, $w, $e = NULL, 0);</PRE
></TD
></TR
></TABLE
>
     </P
></BLOCKQUOTE
></DIV
><P
>&#13;     The <TT
CLASS="parameter"
><I
>tv_sec</I
></TT
> and <TT
CLASS="parameter"
><I
>tv_usec</I
></TT
>
     together form the <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>timeout</I
></SPAN
> parameter. The
     <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>timeout</I
></SPAN
> is an upper bound on the amount of time
     elapsed before <B
CLASS="function"
>socket_select()</B
> return.
     <TT
CLASS="parameter"
><I
>tv_sec</I
></TT
> may be zero , causing
     <B
CLASS="function"
>socket_select()</B
> to return immediately. This is useful
     for polling. If <TT
CLASS="parameter"
><I
>tv_sec</I
></TT
> is <TT
CLASS="constant"
><B
>NULL</B
></TT
> (no timeout),
     <B
CLASS="function"
>socket_select()</B
> can block indefinitely.
    </P
><P
>&#13;     On success <B
CLASS="function"
>socket_select()</B
> returns the number of
     socket resorces contained in the modified arrays, which may be zero if
     the timeout expires before anything interesting happens. On error <TT
CLASS="constant"
><B
>FALSE</B
></TT
>
     is returned. The error code can be retrieved with
     <A
HREF="function.socket-last-error.html"
><B
CLASS="function"
>socket_last_error()</B
></A
>.
    </P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
     Be sure to use the <TT
CLASS="literal"
>===</TT
> operator when checking for an
     error. Since the <B
CLASS="function"
>socket_select()</B
> may return 0 the
     comparison with <TT
CLASS="literal"
>==</TT
> would evaluate to <TT
CLASS="constant"
><B
>TRUE</B
></TT
>:
     <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>if (false === socket_select($r, $w, $e = NULL, 0)) {
    echo "socket_select() failed, reason: " . socket_strerror(socket_last_error()) . "\n";
}</PRE
></TD
></TR
></TABLE
>
     </P
></BLOCKQUOTE
></DIV
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
      Be aware that some socket implementations need to be handled very
      carefully. A few basic rules:
      <P
></P
><UL
><LI
><P
>&#13;         You should always try to use <B
CLASS="function"
>socket_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
>&#13;         No socket resource must be added to any set if you do not intend to
         check its result after the <B
CLASS="function"
>socket_select()</B
> call,
         and respond appropriately. After <B
CLASS="function"
>socket_select()</B
>
         returns, all socket resources in all arrays must be checked. Any
         socket resource that is available for writing must be written to, and
         any socket resource available for reading must be read from.
        </P
></LI
><LI
><P
>&#13;         If you read/write to a socket returns 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
><LI
><P
>&#13;         It's common to most socket implementations that the only exception
         caught with the <TT
CLASS="parameter"
><I
>except</I
></TT
> array is out-of-bound
         data received on a socket.
        </P
></LI
></UL
>
     </P
></BLOCKQUOTE
></DIV
><P
>&#13;     See also
     <A
HREF="function.socket-read.html"
><B
CLASS="function"
>socket_read()</B
></A
>,
     <A
HREF="function.socket-write.html"
><B
CLASS="function"
>socket_write()</B
></A
>,
     <A
HREF="function.socket-last-error.html"
><B
CLASS="function"
>socket_last_error()</B
></A
> and 
     <A
HREF="function.socket-strerror.html"
><B
CLASS="function"
>socket_strerror()</B
></A
>.
    </P
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