SOCKET_SELECT(3)							 1							  SOCKET_SELECT(3)

socket_select - Runs the select() system call on the given arrays of sockets with a specified timeout

SYNOPSIS

       int socket_select (array  &$read, array	&$write, array	&$except, int  $tv_sec, [int  $tv_usec])

DESCRIPTION

       socket_select(3)  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.

PARAMETERS

	      o $read
		- The sockets listed in the $read 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 socket_read(3) will
		return a zero length string).

	      o $write
		- The sockets listed in the $write array will be watched to see if a write will not block.

	      o $except
		- The sockets listed in the $except array will be watched for exceptions.

	      o $tv_sec
		- The $tv_sec and $tv_usec together form the timeout parameter. The timeout is an upper bound on the amount of time elapsed before
		socket_select(3)  return.  $tv_sec  may  be  zero , causing socket_select(3) to return immediately. This is useful for polling. If
		$tv_sec is NULL (no timeout), socket_select(3) can block indefinitely.

	      o $tv_usec
		-

       Warning

	       On exit, the arrays are modified to indicate which socket resource actually changed status.

	You do not need to pass every array to socket_select(3). You can leave it out and use an empty array or NULL instead. Also do  not  forget
       that those arrays are passed by reference and will be modified after socket_select(3) returns.

       Note

	       Due  a  limitation in the current Zend Engine it is not possible to pass a constant modifier like NULL 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:

	      Example #1

		     Using NULL with socket_select(3)

		     <?php
		     $e = NULL;
		     socket_select($r, $w, $e, 0);
		     ?>

RETURN VALUES

	On  success  socket_select(3)  returns	the  number of socket resources contained in the modified arrays, which may be zero if the timeout
       expires before anything interesting happens. On error FALSE is returned. The error code can be retrieved with socket_last_error(3).

       Note

	       Be sure to use the === operator when checking for an error. Since the socket_select(3) may return 0 the comparison  with  ==  would
	      evaluate to TRUE:

	      Example #2

		     Understanding socket_select(3)'s result

		     <?php
		     $e = NULL;
		     if (false === socket_select($r, $w, $e, 0)) {
			 echo "socket_select() failed, reason: " .
			     socket_strerror(socket_last_error()) . "
";
		     }
		     ?>

EXAMPLES

       Example #3

	      socket_select(3) example

	      <?php
	      /* Prepare the read array */
	      $read   = array($socket1, $socket2);
	      $write  = NULL;
	      $except = NULL;
	      $num_changed_sockets = socket_select($read, $write, $except, 0);

	      if ($num_changed_sockets === false) {
		  /* Error handling */
	      } else if ($num_changed_sockets > 0) {
		  /* At least at one of the sockets something interesting happened */
	      }
	      ?>

NOTES

       Note

	       Be aware that some socket implementations need to be handled very carefully. A few basic rules:

		     o	You  should always try to use socket_select(3) 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.

		     o No socket resource must be added to any set if you do not intend to check its result after the socket_select(3)	call,  and
		     respond  appropriately.  After  socket_select(3)  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.

		     o 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.

		     o	It's  common  to  most	socket	implementations that the only exception caught with the $except array is out-of-bound data
		     received on a socket.

SEE ALSO

       socket_read(3), socket_write(3), socket_last_error(3), socket_strerror(3).

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