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.
stream_select
(PHP 4 >= 4.3.0, PHP 5, PHP 7, PHP 8)
stream_select — Ejecuta el equivalente de la llamada al sistema select() sobre las matrices de flujos dadas con un tiempo de espera especificado por tv_sec y tv_usec
Descripción
La función stream_select() acepta matrices de flujos y espera a que cambien su estado. Su operación es equivalente a la de la función socket_select() excepto que actúa sobre flujos.
Parámetros
-
read -
Los flujos listados en la matriz
readserán observados para comprobar si los caracteres están disponibles para la lectura (de manera más precisa, para ver si una lectura no bloqueará - en particular, un recurso de flujo está también listo en el final de archivo, en cuyo caso una llamada a fread() devolverá una cadena de longitud cero). -
write -
Los flujos listados en la matriz
writeserán observados para comprobar si una escritura no bloqueará. -
except -
Los flujos listados en la matriz
exceptserán observados para una llegada de información excepcional de alta prioridad ("fuera de banda").
No se necesita pasar cada matriz a stream_select(). Se pueden omitir y usar una matriz vacía oNota:
Cuando stream_select() devuelve, las matrices
read,writeyexceptse modifican para indicar qué recursos de flujo cambiaron de estado actualmente.nullen su lugar. No se olvide también de que estas matrices son pasadas por referencia y serán modificadas después de que stream_select() devuelva. -
tv_sec -
Los parámetros
tv_secytv_usecforman juntos el parámetro timeout,tv_secespecifica el número de segundos mientras quetv_usecespecifica el número de microsegundos. Eltimeout(tiemop de espera) es un límite superior de la cantidad de tiempo que stream_select() esperará antes de devolver. Sitv_secytv_usecestán establecidos a0, stream_select() no esperará información - en su lugar devolverá inmediantamente, indicando el estado acutal de los flujos.Si
tv_secesnullstream_select() puede bloquear indefinidamente, devolviendo sólo cuando ocurra un evento de los flujos observados (o si una señal interrumpe la llamada al sistema).AdvertenciaUsar un valor de tiempo de espera de
0permite emitir instantáneamente el estado de los flujos, sin embargo, NO es una buena idea usar un valor de tiempo de espera de0en un bucle ya que causará que el script consuma demasiado tiempo de la CPU.Es mucho mejor especificar un valor de tiempo de espera de unos pocos segundos, aunque si se necesita comprobar y ejecutar actualmente otro código, usar un valor de tiempo de espera de al menos
200000microsegundos ayudará a reducir el uso de la CPU del script.Recuerde que el valor del tiempo de espera es el tiempo máximo que transcurrirá; stream_select() devolverá tan pronto como los flujos requeridos estén listos para su uso.
-
tv_usec -
Véase la descripción de
tv_sec.
Valores devueltos
Si se tuvo éxito stream_select() devolverá el número de
recursos de flujo contenidos en las matrices modificadas, lo cual puede ser cero si
el tiempo de espera expira antes de que no ocurra nada interesante. Si se produjo un error
devolverá false y se lanzará una advertendia (esto puede suceder si la llamada al sistema es
interrumpida por una señal entrante).
Ejemplos
Ejemplo #1 Ejemplo de stream_select()
Este ejemplo hace una comprobación para ver si ha llegado información para leer sobre
$stream1 o $stream2.
Ya que el tiempo de espera es 0 devolverá
inmediatamente:
<?php
/* Prepararse para leer una matriz */
$read = array($stream1, $stream2);
$write = NULL;
$except = NULL;
if (false === ($num_changed_streams = stream_select($read, $write, $except, 0))) {
/* Manejo de errores */
} elseif ($num_changed_streams > 0) {
/* Sucedió algo interesante en al menos uno de los flujos */
}
?>Notas
Nota:
Debido a las limitaciones en el actual Zend Engine no es posible pasar un modificador constante como
nulldirectamente como un parámetro a una función que espera que este parámetro sea pasado por referencia. En su lugar use una variable temporal o una expresión con el miembro más a la izquierda como una variable temporal:<?php
$e = NULL;
stream_select($r, $w, $e, 0);
?>
Nota:
Asegúrese de usar el operador
===cuando se compruebe un error. Ya que stream_select() puede devolver 0, la comparación con==sería evaluada comotrue:<?php
$e = NULL;
if (false === stream_select($r, $w, $e, 0)) {
echo "Falló stream_select()\n";
}
?>
Nota:
Si se lee/escribe en un flujo devuelto en las matrices sea consciente de que éstas no leen/escriben necesariamente la cantidad total de información que se solicitó. Inluso sólo pueden ser capaces de leer/escribir un sólo byte.
Nota:
Algunos flujos (como
zlib) no pueden ser seleccionados por esta función.
Nota:
Compatibilidad con Windows: stream_select() usado sobre una tubería devuelta desde proc_open() puede causar pérdida de información bajo Windows 98.
El uso de stream_select() sobre descriptores de archivos devueltos por proc_open() fallará y devolverá
falsebajo Windows.
Ver también
- stream_set_blocking() - Establecer el modo bloqueo/no-bloqueo en un flujo
add a note
User Contributed Notes 17 notes
php at richardneill dot org ¶
15 years ago
maartenwolzak at gmail dot com ¶
17 years ago
Note that you should change the calctimeout function below to divide the outcome by 1.000.000 otherwise you'll be waiting for two years instead of one minute for the socket to timeout...
<?php
// The function to calculate the timeout
function calctimeout($maxtime, $starttime)
{
return ($maxtime - ((microtime(true) - $starttime) * 1000000))/1000000;
}
?>
Martin ¶
6 years ago
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;
}
}
}
}
?>
aidan at php dot net ¶
20 years ago
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;
}
?>
doingitwrong at mailismagic dot com ¶
9 years ago
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.
Sitsofe ¶
5 years ago
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)
rob at associatedtechs dot com ¶
10 years ago
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.
mark2xv at gmail dot com ¶
11 years ago
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.)
phpdoc at shemesh dot biz ¶
19 years ago
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.
lynch at php dot net ¶
14 years ago
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
Ben ¶
17 years ago
You can key on file descriptors just fine by casting them to an int or a string, which returns what you would expect.
aidan at aidans dot org ¶
18 years ago
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!
jerrywilborn at gmail dot com ¶
15 years ago
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.
asphp at dsgml dot com ¶
8 years ago
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.
bluej100@gmail ¶
17 years ago
@mbaynton at gmail dot com
A handy syntactic trick:
<?php
$r = Array($stream1, $stream2);
stream_select($r, $w = null, $x = null, 1337);
?>
I've seen it recommended elsewhere in the documentation for clarifying magic arguments so maintainers don't have to go check the function itself, but it also solves your problem here.
aks at esoft dot dk ¶
14 years ago
stream_select() looks deceptively like a simple wrapper around POSIX select(2).
But beware: while select(2) allows you to pass no file descriptors and use it as a "portable subsecond sleep", PHP will complain with "Warning: stream_select(): No stream arrays were passed in ****" if all arrays are empty or null, and it WONT sleep, it will return immediately. So... if the number of file descriptors you have isn't static, you have to deal with the special case yourself.
Maxdamantus ¶
17 years ago
Simple stream_select wrapper.. Returns the first stream in the array, and sets parameter 2 to the key (So that it is easy to identify what received data):
<?php
function select($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";
}
?>
