stream_select

aks at esoft dot dk (2010-11-10 07:56:21)

stream_select() looks deceptively like a simple wrapper around POSIX select(2).
But beware: while select(2) allows you to pass no file descriptors and use it as a "portable subsecond sleep", PHP will complain with "Warning: stream_select(): No stream arrays were passed in ****" if all arrays are empty or null, and it WONT sleep, it will return immediately. So... if the number of file descriptors you have isn't static, you have to deal with the special case yourself.

lynch at php dot net (2010-03-15 12:48:32)

Note: At least one of the input arrays must be non-empty, or you get an E_WARNING message:
PHP Warning: stream_select(): unable to select [9]: Bad file descriptor (max_fd=0) in

jerrywilborn at gmail dot com (2009-07-27 10:55:09)

http://bugs.php.net/bug.php?id=42682
This function will not return the number of changed streams under certain systems with older versions, but instead it will return '0'. Be careful.

php at richardneill dot org (2009-07-04 19:45:55)

Note that reading from a regular file which is on end-of-file will *not* block. You'll get a non-blocking, zero-byte read. However, stream_select *will* block if the input is a pipe, and there is no more data to be had.

Maxdamantus (2007-09-29 22:28:11)

Simple stream_select wrapper.. Returns the first stream in the array, and sets parameter 2 to the key (So that it is easy to identify what received data):

<?php
function select($array, &$vkey, $timeout=0){
    $select = array();
    $null = NULL;
    foreach($array as $key => $sock){
        $x = count($select);
        $select[$x] = $sock;
        $keys[$x] = $key;
    }
    if(stream_select($select, $null, $null, $timeout)){
        foreach($keys as $key){
            if($array[$key] == $select[0]){
                $vkey = $key;
                return($select[0]);
            }
        }
    }
}

$streams = array("foo" => $stream_one, "bar" => $stream_two); // Create an array of two (already existant) streams.
if($new = select($streams, $key, 60)){ //Sets $new to the resource that next gets new data, and $key to either "foo", or "bar", depending which one it is.
    echo $key.":".stream_get_line($new, 2048)."\n";
}
?>

bluej100@gmail (2007-08-21 16:31:09)

@mbaynton at gmail dot com

A handy syntactic trick:

<?php
$r = Array($stream1, $stream2);
stream_select($r, $w = null, $x = null, 1337);
?>

I've seen it recommended elsewhere in the documentation for clarifying magic arguments so maintainers don't have to go check the function itself, but it also solves your problem here.

mbaynton at gmail dot com (2007-08-17 07:35:35)

The documentation states that:
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 appears to be incorrect, at least in PHP 5.1.6, because PHP sees these parameters are passed by reference and thus insists on a bona fide variable for the reference to refer to:
Fatal error: Only variables can be passed by reference
is what you get if you pass NULL or anything else literally.

Ben (2007-02-01 17:35:10)

You can key on file descriptors just fine by casting them to an int or a string, which returns what you would expect.

maartenwolzak at gmail dot com (2007-01-25 01:36:00)

Note that you should change the calctimeout function below to divide the outcome by 1.000.000 otherwise you'll be waiting for two years instead of one minute for the socket to timeout...

<?php

// The function to calculate the timeout
function calctimeout($maxtime, $starttime)
{
   return ($maxtime - ((microtime(true) - $starttime) * 1000000))/1000000;
}

?>

aidan at aidans dot org (2006-12-07 19:53:39)

Note that contrary to what the previous poster said, one is not able to use a stream resource as a key for an array. Rather, if you want to know which socket you are dealing with, consider using code similar to this:

<?php
$sockets = array("sock_1" => $sock1, "sock_2" => $sock2, "sock_3" => $sock_3);

$read = $write = $error = $sockets;
$num = stream_select($read, $write, $error, 10);
if ($n > 0) {
    foreach ($read as $r) {
        $key = array_search($r, $sockets);
        // $key will be "sock_1", "sock_2", "sock_3", etc.
    }
}
?>

Hope that helps someone out there!

phpdoc at shemesh dot biz (2005-03-14 01:33:10)

Please note that, on return, the key of "read" will be zero based, serially numbered according to the streams for which there is read data ready only. In other words, if you want to know which of the original streams placed in "read" is ready, there is no immediate way of knowing that.
If you want to know which of the original stream is which, you can either use "==", or possibly set a reverse map array, in which the stream is the key, and the key to the original "read" array is the data.

aidan at php dot net (2004-06-22 11:30:23)

If you want to set an absolute maximum execution time for stream_select in a loop, it's important to decrement the max_time value passed to stream_select.

<?php
// The maximum time for execution in milliseconds
$maxtime = 200000;
// The time the loop started
$starttime = microtime(true);
// Original array of sockets
$r = $orig_sockets;

// The function to calculate the timeout
function calctimeout($maxtime, $starttime)
{
    return $maxtime - ((microtime(true) - $starttime) * 1000000);
}

while (stream_select($r, $w = null, $e = null, 0, calctimeout($maxtime, $starttime)) !== 0)
{
    // loop through the sockets that showed activity
    foreach ($r as $socket) {
        // $socket talked
    }

    // stream_select modifies the contents of $r
    // in a loop we should replace it with the original
    $r = $orig_sockets;
}

?>