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socket_select

socket_select

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

 **socket_select**  $read  $write  $except  $seconds int $microseconds

accepts arrays of sockets and waits for

them to change status. Those coming with BSD sockets background will recognize that those socket arrays are in fact the so-called file descriptor sets. Three independent arrays of sockets are watched. socket_select

read The sockets listed in the 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 is also ready on end-of-file, in which case a will return a zero length string). read``socket_read

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

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

seconds The and together form the parameter. The is an upper bound on the amount of time elapsed before return. may be zero , causing to return immediately. This is useful for polling. If is null (no timeout), can block indefinitely. seconds``microseconds``timeout``timeout``socket_select``seconds``socket_select``seconds``socket_select

microseconds

Waarschuwing: > On exit, the arrays are modified to indicate which socket actually changed status.

You do not need to pass every array to . You can leave it out and use an empty array or null instead. Also do not forget that those arrays are passed and will be modified after returns. socket_selectby referencesocket_select

Opmerking: > 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:

**Voorbeeld: Using null with **

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

On success returns the number of sockets 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_select``socket_last_error

Opmerking: > Be sure to use the operator when checking for an error. Since the may return 0 the comparison with would evaluate to true:

===``socket_select``==Voorbeeld: Understanding 's result

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

Voorbeeld: 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 */
}
?>

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

  • You should always try to use 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. socket_select
  • No socket must be added to any set if you do not intend to check its result after the call, and respond appropriately. After returns, all sockets in all arrays must be checked. Any socket that is available for writing must be written to, and any socket available for reading must be read from. socket_select``socket_select
  • 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.
  • It's common to most socket implementations that the only exception caught with the array is out-of-bound data received on a socket. except

socket_read``socket_write``socket_last_error``socket_strerror

Vorige ← socket_recvmsg Volgende socket_send →

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