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                                 stream_select

   (PHP 4 >= 4.3.0)
   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

Description

   int stream_select ( resource &read, resource &write, resource &except,
   int tv_sec [, int tv_usec])

   The stream_select() function accepts arrays of streams and waits for
   them to change status. Its operation is equivalent to that of the
   socket_select() function except in that it acts on streams.

   The streams 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 stream resource is also ready
   on end-of-file, in which case an fread() will return a zero length
   string).

   The streams listed in the write array will be watched to see if a
   write will not block.

   The streams listed in the except array will be watched for high
   priority exceptional ("out-of-band") data arriving.

     Note: When stream_select() returns, the arrays read, write and
     except are modified to indicate which stream resource(s) actually
     changed status.

   The tv_sec and tv_usec together form the timeout parameter, tv_sec
   specifies the number of seconds while tv_usec the number of
   microseconds. The timeout is an upper bound on the amount of time that
   stream_select() will wait before it returns. If tv_sec and tv_usec are
   both set to 0, stream_select() will not wait for data - instead it
   will return immediately, indicating the current status of the streams.
   If tv_sec is NULL stream_select() can block indefinitely, returning
   only when an event on one of the watched streams occurs (or if a
   signal interrupts the system call).

   On success stream_select() 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 FALSE is
   returned and a warning raised (this can happen if the system call is
   interrupted by an incoming signal).

   Warning

   Using a timeout value of 0 allows you to instantaneously poll the
   status of the streams, however, it is NOT a good idea to use a 0
   timeout value in a loop as it will cause your script to consume too
   much CPU time.

   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 200000 microseconds
   will help reduce the CPU usage of your script.

   Remember that the timeout value is the maximum time that will elapse;
   stream_select() will return as soon as the requested streams are ready
   for use.

   You do not need to pass every array to stream_select(). 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
   stream_select() returns.

   This example checks to see if data has arrived for reading on either
   $stream1 or $stream2. Since the timeout value is 0 it will return
   immediately:
   <?php
   /* Prepare the read array */
   $read = array($stream1, $stream2);
   if (false === ($num_changed_streams = stream_select($read, $write =
   NULL, $except = NULL, 0))) {
       /* Error handling */
   } elseif ($num_changed_streams > 0) {
       /* At least on one of the streams something interesting happened
   */
   }
   ?>

     Note: Due to 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:

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

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

   <?php
   if (false === stream_select($r, $w, $e = NULL, 0)) {
       echo "stream_select() failed\n";
   }
   ?>

     Note: 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.

     Windows 98 Note: stream_select() used on a pipe returned from
     proc_open() may cause data loss under Windows 98.

   See also stream_set_blocking()
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