stream_select()

(PHP 4 >= 4.3.0, PHP 5, PHP 7)

Runs the equivalent of the select() system call on the given arrays of streams with a timeout specified by tv_sec and tv_usec

说明

stream_select(array &$read,array &$write,array &$except,int $tv_sec[,int $tv_usec= 0]): int

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

参数

$read

The streams listed in the$readarray 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 anfread()will return a zero length string).

$write

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

$except

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

Note:

Whenstream_select()returns, the arrays$read,$writeand$exceptare modified to indicate which stream resource(s) actually changed status.

You do not need to pass every array tostream_select(). You can leave it out and use an empty array orNULLinstead. Also do not forget that those arrays are passedby referenceand will be modified afterstream_select()returns.

$tv_sec

The$tv_secand$tv_usectogether form thetimeoutparameter,$tv_secspecifies the number of seconds while$tv_usecthe number of microseconds.The$timeoutis an upper bound on the amount of time thatstream_select()will wait before it returns.If$tv_secand$tv_usecare both set to0,stream_select()will not wait for data - instead it will return immediately, indicating the current status of the streams.

If$tv_secisNULLstream_select()can block indefinitely, returning only when an event on one of the watched streams occurs (or if a signal interrupts the system call).

Warning

Using a timeout value of0allows you to instantaneously poll the status of the streams, however, it is NOT a good idea to use a0timeout 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 least200000microseconds 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.

$tv_usec

See$tv_secdescription.

返回值

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

范例

Example #1stream_select()Example

This example checks to see if data has arrived for reading on either$stream1or$stream2. Since the timeout value is0it will return immediately:

<?php
/* Prepare the read array */
$read   = array($stream1, $stream2);
$write  = NULL;
$except = NULL;
if (false === ($num_changed_streams = stream_select($read, $write, $except, 0))) {
    /* Error handling */
} elseif ($num_changed_streams > 0) {
    /* At least on one of the streams something interesting happened */
}
?>

注释

Note:

Due to a limitation in the current Zend Engine it is not possible to pass a constant modifier likeNULLdirectly 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 $e = NULL; stream_select($r, $w, $e, 0); ?>

Note:

Be sure to use the===operator when checking for an error. Since thestream_select()may return 0 the comparison with==would evaluate toTRUE:<?php $e = NULL; if (false === stream_select($r, $w, $e, 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.

Note:

Some streams (likezlib) cannot be selected by this function.

Note:

Windows compatibility:stream_select()used on a pipe returned fromproc_open()may cause data loss under Windows 98.

Use ofstream_select()on file descriptors returned byproc_open()will fail and returnFALSEunder Windows.

参见

• stream_set_blocking() 为资源流设置阻塞或者阻塞模式

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;
}
?>

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;
}
?>

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.

Maintaining connection with multiple clients can be tricky, PHP script is single-thread process, so if you like to do more than one thing at once (like waiting for new connections and waiting for new data), you’ll have to use some sort of multiplexing. 
<?php
$socket = stream_socket_server("tcp://0.0.0.0:8000", $errno, $errstr, STREAM_SERVER_BIND | STREAM_SERVER_LISTEN);
stream_set_blocking($socket, 0);
$connections = [];
$read = [];
$write = null;
$except = null;
while (1) {
  // look for new connections
  if ($c = @stream_socket_accept($socket, empty($connections) ? -1 : 0, $peer)) {
    echo $peer.' connected'.PHP_EOL;
    fwrite($c, 'Hello '.$peer.PHP_EOL);
    $connections[$peer] = $c;
  }
  // wait for any stream data
  $read = $connections;
  if (stream_select($read, $write, $except, 5)) {
    foreach ($read as $c) {
      $peer = stream_socket_get_name($c, true);
      if (feof($c)) {
        echo 'Connection closed '.$peer.PHP_EOL;
        fclose($c);
        unset($connections[$peer]);
      } else {
        $contents = fread($c, 1024);
        echo $peer.': '.trim($contents).PHP_EOL;
      }
    }
  }
}
?>

If you use stream_select() with a blocking stream, you are doing it wrong!
Just because this function returns something in one or more of the arrays does NOT mean that a future read or write operation will not block.
The above sentence is the most important sentence you will ever read regarding stream manipulation. Using stream_select() with blocking streams is a very common amateur mistake and causes major headaches when tracking down usage of this and similar select() system functions. PHP (and really the underlying OS) should verify that the supplied stream set is not blocking and throw an error/exception if any socket is set to block so that people are forced to fix their code. The documentation for stream_select() is, at best, misleading.
If you want a non-blocking stream, then set the stream to not block. Otherwise, live with the blocking stream. That is, after all, the whole point of blocking - to block indefinitely until the operation completes. select() is built for non-blocking streams ONLY. Any other use will result in very hard to track down bugs.
I got the above lecture many years ago after encountering the very bugs I mention. I fixed my code and now correct similar mistakes when I run into the issue elsewhere. Writing code for non-blocking streams is simpler than trying to write hacks for blocking streams with select() functions and ending up with application bugs.

If you try to use stream_select() with fread(), you may get bit by a combination of bugs (https://bugs.php.net/bug.php?id=52602 and https://bugs.php.net/bug.php?id=51056). As of PHP 5.5.10, fread() and stream_select() don't reliably play well together.
If you need stream_select() and you don't need an encrypted connection (e.g. TLS), use stream_socket_recvfrom() instead of fread().
I can't find a way to reliably handle an encrypted connection with blocking functions in PHP; non-blocking might be the only way to do it.

If you're getting unexplainable problems with nonblocking sockets using stream_select, disable the buffers using:
stream_set_read_buffer($socket, 0);
stream_set_write_buffer($socket, 0);
For some reason when writing (in total) ~256k, sockets start returning FALSE when reading, yet always appear in the stream_select arrays. This fixed that problem. (for us.)

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.

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

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

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!

Make sure not to pass the same variable in the 3 arguments to stream_select, or you'll only get the results from one of them and the others will be overwritten.

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.

When stream_select() fails you SHOULD NOT use the results of the arrays (i.e. read, write, except) that were passed into it as parameters. While doing so anyway won't trigger undefined behaviour, you are depending on unspecified behaviour that by definition is not guaranteed.
At the time of writing the PHP 7.2 interpreter does not modify the arrays upon stream_select() failure (see the code around https://github.com/php/php-src/blob/php-7.2.14/ext/standard/streamsfuncs.c#L842) thus a PHP program that doesn't heed the advice above can deceive itself as to the state of those streams.
(Hopefully this warning can be added to the main documentation one day)

@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.

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.

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";
}
?>