It looks like msg_receive() allocates a memory with size $maxsize, and only then tries to receive a message from queue into allocated memory. Because my script dies with $maxsize = 1 Gib, but works with $maxsize = 10 Kib.
(PHP 4 >= 4.3.0, PHP 5, PHP 7, PHP 8)
msg_receive — Receive a message from a message queue
$queue,$desired_message_type,&$received_message_type,$max_message_size,&$message,$unserialize = true,$flags = 0,&$error_code = null
msg_receive() will receive the first message from the
specified queue of the type specified by
desired_message_type.
queueThe message queue.
desired_message_type
If desired_message_type is 0, the message from the front
of the queue is returned. If desired_message_type is
greater than 0, then the first message of that type is returned.
If desired_message_type is less than 0, the first
message on the queue with a type less than or equal to the
absolute value of desired_message_type will be read.
If no messages match the criteria, your script will wait until a suitable
message arrives on the queue. You can prevent the script from blocking
by specifying MSG_IPC_NOWAIT in the
flags parameter.
received_message_typeThe type of the message that was received will be stored in this parameter.
max_message_size
The maximum size of message to be accepted is specified by the
max_message_size; if the message in the queue is larger
than this size the function will fail (unless you set
flags as described below).
message
The received message will be stored in message,
unless there were errors receiving the message.
unserialize
If set to
true, the message is treated as though it was serialized using the
same mechanism as the session module. The message will be unserialized
and then returned to your script. This allows you to easily receive
arrays or complex object structures from other PHP scripts, or if you
are using the WDDX serializer, from any WDDX compatible source.
If unserialize is false, the message will be
returned as a binary-safe string.
flags
The optional flags allows you to pass flags to the
low-level msgrcv system call. It defaults to 0, but you may specify one
or more of the following values (by adding or ORing them together).
MSG_IPC_NOWAIT |
If there are no messages of the
desired_message_type, return immediately and do not
wait. The function will fail and return an integer value
corresponding to MSG_ENOMSG.
|
MSG_EXCEPT |
Using this flag in combination with a
desired_message_type greater than 0 will cause the
function to receive the first message that is not equal to
desired_message_type. |
MSG_NOERROR |
If the message is longer than max_message_size,
setting this flag will truncate the message to
max_message_size and will not signal an error.
|
error_code
If the function fails, the optional error_code
will be set to the value of the system errno variable.
Returns true on success or false on failure.
Upon successful completion the message queue data structure is updated as
follows: msg_lrpid is set to the process-ID of the
calling process, msg_qnum is decremented by 1 and
msg_rtime is set to the current time.
| Version | Description |
|---|---|
| 8.0.0 |
queue expects a SysvMessageQueue
instance now; previously, a resource was expected.
|
It looks like msg_receive() allocates a memory with size $maxsize, and only then tries to receive a message from queue into allocated memory. Because my script dies with $maxsize = 1 Gib, but works with $maxsize = 10 Kib.<?php error_reporting(E_ALL);
/**
* Example for sending and receiving Messages via the System V Message Queue
*
* To try this script run it synchron/asynchron twice times. One time with ?typ=send and one time with ?typ=receive
*
* @author Thomas Eimers - Mehrkanal GmbH
*
* This document is distributed in the hope that it will be useful, but without any warranty;
* without even the implied warranty of merchantability or fitness for a particular purpose.
*/
header('Content-Type: text/plain; charset=ISO-8859-1');
echo "Start...\n";
// Create System V Message Queue. Integer value is the number of the Queue
$queue = msg_get_queue(100379);
// Sendoptions
$message='nachricht'; // Transfering Data
$serialize_needed=false; // Must the transfer data be serialized ?
$block_send=false; // Block if Message could not be send (Queue full...) (true/false)
$msgtype_send=1; // Any Integer above 0. It signeds every Message. So you could handle multible message
// type in one Queue.
// Receiveoptions
$msgtype_receive=1; // Whiche type of Message we want to receive ? (Here, the type is the same as the type we send,
// but if you set this to 0 you receive the next Message in the Queue with any type.
$maxsize=100; // How long is the maximal data you like to receive.
$option_receive=MSG_IPC_NOWAIT; // If there are no messages of the wanted type in the Queue continue without wating.
// If is set to NULL wait for a Message.
// Send or receive 20 Messages
for ($i=0;$i<20;$i++) {
sleep(1);
// This one sends
if ($_GET['typ']=='send') {
if(msg_send($queue,$msgtype_send, $message,$serialize_needed, $block_send,$err)===true) {
echo "Message sendet.\n";
} else {
var_dump($err);
}
// This one received
} else {
$queue_status=msg_stat_queue($queue);
echo 'Messages in the queue: '.$queue_status['msg_qnum']."\n";
// WARNUNG: nur weil vor einer Zeile Code noch Nachrichten in der Queue waren, muss das jetzt nciht mehr der Fall sein!
if ($queue_status['msg_qnum']>0) {
if (msg_receive($queue,$msgtype_receive ,$msgtype_erhalten,$maxsize,$daten,$serialize_needed, $option_receive, $err)===true) {
echo "Received data".$daten."\n";
} else {
var_dump($err);
}
}
}
}
?>It seems that a maxsize of 2Mb is some sort of a threshold for php, above that msg_receive() starts to use a lot of CPU (with a sender that is pushing messages non-stop receiving 10000 messages jumps up from 0.01 sec to 1.5 sec on my computer) so try to stay below that thresholod if you can.Consider this e.g. Linux situation:
<?php
//file send.php
$ip = msg_get_queue(12340);
msg_send($ip,8,"abcd",false,false,$err);
//-----------------------------------------------------
<?php
//file receive.php
$ip = msg_get_queue(12340);
msg_receive($ip,0,$msgtype,4,$data,false,null,$err);
echo "msgtype {$msgtype} data {$data}\n";
msg_receive($ip,0,$msgtype,4,$data,false,null,$err);
echo "msgtype {$msgtype} data {$data}\n";
?>
Now run:
in terminal #1 php5 receive.php
in terminal #2 php5 receive.php
in terminal #3 php5 send.php
Showing messages from queue will flip-flop. It means you run once send.php, the message will be shown in terminal #1. Second run it will be in t#2, third #1 and so on.This is meant to be run as your apache user in a terminal, call script in note of msg_send and they will communicate.
#! /usr/bin/env php
<?php
$MSGKEY = 519051; // Message
$msg_id = msg_get_queue ($MSGKEY, 0600);
while (1) {
if (msg_receive ($msg_id, 1, $msg_type, 16384, $msg, true, 0, $msg_error)) {
if ($msg == 'Quit') break;
echo "$msg\n";
} else {
echo "Received $msg_error fetching message\n";
break;
}
}
msg_remove_queue ($msg_id);
?>