(PHP 4 >= 4.1.0, PHP 5)
socket_create_pair — Creates a pair of indistinguishable sockets and stores them in an array
$domain
   , int $type
   , int $protocol
   , array &$fd
   )
   socket_create_pair() creates two connected and
   indistinguishable sockets, and stores them in fd.
   This function is commonly used in IPC (InterProcess Communication).
  
domain
       The domain parameter specifies the protocol
       family to be used by the socket. See socket_create()
       for the full list.
      
type
       The type parameter selects the type of communication
       to be used by the socket. See socket_create() for the 
       full list.
      
protocol
       The protocol parameter sets the specific
       protocol within the specified domain to be used
       when communicating on the returned socket. The proper value can be retrieved by
       name by using getprotobyname(). If
       the desired protocol is TCP, or UDP the corresponding constants
       SOL_TCP, and SOL_UDP
       can also be used.
      
See socket_create() for the full list of supported protocols.
fdReference to an array in which the two socket resources will be inserted.
   Returns TRUE on success or FALSE on failure.
  
| Version | Description | 
|---|---|
| 5.3.0 | This function is now re-enabled on Windows platforms. | 
| 4.3.0 | This function was due to a bug made unavailable on Windows platforms. | 
Example #1 socket_create_pair() example
<?php
$sockets = array();
/* On Windows we need to use AF_INET */
$domain = (strtoupper(substr(PHP_OS, 0, 3)) == 'WIN' ? AF_INET : AF_UNIX);
/* Setup socket pair */
if (socket_create_pair($domain, SOCK_STREAM, 0, $sockets) === false) {
    echo "socket_create_pair failed. Reason: ".socket_strerror(socket_last_error());
}
/* Send and Recieve Data */
if (socket_write($sockets[0], "ABCdef123\n", strlen("ABCdef123\n")) === false) {
    echo "socket_write() failed. Reason: ".socket_strerror(socket_last_error($sockets[0]));
}
if (($data = socket_read($sockets[1], strlen("ABCdef123\n"), PHP_BINARY_READ)) === false) {
    echo "socket_read() failed. Reason: ".socket_strerror(socket_last_error($sockets[1]));
}
var_dump($data);
/* Close sockets */
socket_close($sockets[0]);
socket_close($sockets[1]);
?>
Example #2 socket_create_pair() IPC example
<?php
$ary = array();
$strone = 'Message From Parent.';
$strtwo = 'Message From Child.';
if (socket_create_pair(AF_UNIX, SOCK_STREAM, 0, $ary) === false) {
    echo "socket_create_pair() failed. Reason: ".socket_strerror(socket_last_error());
}
$pid = pcntl_fork();
if ($pid == -1) {
    echo 'Could not fork Process.';
} elseif ($pid) {
    /*parent*/
    socket_close($ary[0]);
    if (socket_write($ary[1], $strone, strlen($strone)) === false) {
        echo "socket_write() failed. Reason: ".socket_strerror(socket_last_error($ary[1]));
    }
    if (socket_read($ary[1], strlen($strtwo), PHP_BINARY_READ) == $strtwo) {
        echo "Recieved $strtwo\n";
    }
    socket_close($ary[1]);
} else {
    /*child*/
    socket_close($ary[1]);
    if (socket_write($ary[0], $strtwo, strlen($strtwo)) === false) {
        echo "socket_write() failed. Reason: ".socket_strerror(socket_last_error($ary[0]));
    }
    if (socket_read($ary[0], strlen($strone), PHP_BINARY_READ) == $strone) {
        echo "Recieved $strone\n";
    }
    socket_close($ary[0]);
}
?>