socket_select
(PHP 4 >= 4.1.0, PHP 5)
socket_select — Runs the select() system call on the given arrays of sockets with a specified timeout
Описание
int socket_select
( array &$read
, array &$write
, array &$except
, int $tv_sec
[, int $tv_usec= 0
] )
Список параметров
-
read
-
The sockets 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 socket
resource is also ready on end-of-file, in which case a
socket_read() will return a zero length string).
-
write
-
The sockets listed in the write
array will be
watched to see if a write will not block.
-
except
-
The sockets listed in the except
array will be
watched for exceptions.
-
tv_sec
-
The tv_sec
and tv_usec
together form the timeout parameter. The
timeout is an upper bound on the amount of time
elapsed before socket_select() return.
tv_sec
may be zero , causing
socket_select() to return immediately. This is useful
for polling. If tv_sec
is NULL (no timeout),
socket_select() can block indefinitely.
-
tv_usec
-
Внимание
On exit, the arrays are modified to indicate which socket resource
actually changed status.
You do not need to pass every array to
socket_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
socket_select() returns.
Замечание:
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:
Пример #1 Using NULL with socket_select()
<?php
$e = NULL;
socket_select($r, $w, $e, 0);
?>
Возвращаемые значения
On success socket_select() returns the number of
socket resources 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_last_error().
Замечание:
Be sure to use the === operator when checking for an
error. Since the socket_select() may return 0 the
comparison with == would evaluate to TRUE:
Пример #2 Understanding socket_select()'s result
<?php
$e = NULL;
if (false === socket_select($r, $w, $e, 0)) {
echo "socket_select() failed, reason: " .
socket_strerror(socket_last_error()) . "\n";
}
?>
Примеры
Пример #3 socket_select() 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 */
}
?>
Примечания
Замечание:
Be aware that some socket implementations need to be handled very
carefully. A few basic rules:
-
You should always try to use socket_select()
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.
-
No socket resource must be added to any set if you do not intend to
check its result after the socket_select() call,
and respond appropriately. After socket_select()
returns, all socket resources in all arrays must be checked. Any
socket resource that is available for writing must be written to, and
any socket resource available for reading must be read from.
-
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 except
array is out-of-bound
data received on a socket.
