msg_get_queue

(PHP 4 >= 4.3.0, PHP 5, PHP 7, PHP 8)

msg_get_queue — Create or attach to a message queue

Descrição

msg_get_queue(int $key, int $permissions = 0666): SysvMessageQueue|false

msg_get_queue() returns an id that can be used to access the System V message queue with the given key. The first call creates the message queue with the optional permissions. A second call to msg_get_queue() for the same key will return a different message queue identifier, but both identifiers access the same underlying message queue.

Parâmetros

key: Message queue numeric ID
permissions: Queue permissions. Default to 0666. If the message queue already exists, the permissions will be ignored.

Valor Retornado

Returns SysvMessageQueue instance that can be used to access the System V message queue, ou false em caso de falha.

Registro de Alterações

Versão	Descrição
8.0.0	On success, this function returns a SysvMessageQueue instance now; previously, a resource was returned.

Veja Também

msg_remove_queue() - Destroy a message queue
msg_receive() - Receive a message from a message queue
msg_send() - Send a message to a message queue
msg_stat_queue() - Returns information from the message queue data structure
msg_set_queue() - Set information in the message queue data structure

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User Contributed Notes 7 notes

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Michael Iatrou ¶

14 years ago


If you are getting the following message (on Linux):



Warning: msg_get_queue() [function.msg-get-queue]: failed for key 0x12345678: No space left on device in /path/to/script.php on line 1



aside from what [others have] suggested, you should also check and set an appropriate value for kernel parameter kernel.msgmni, e.g. sysctl -w kernel.msgmni=256

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david dot schueler at tel-billig dot de ¶

16 years ago


If you are getting this message on your *NIX box:

Warning: msg_get_queue() [function.msg-get-queue]: failed for key 0x12345678: No space left on device in /path/to/script.php on line 1

you may use the command "ipcrm" as root to clear the message queue. Use "man ipcrm" to get more info on it.
The default setting for maximum messages in the queue is stored in /proc/sys/fs/mqueue/msg_max. To increase it to a maximum of 100 messages, just run:
echo 100 > /proc/sys/fs/mqueue/msg_max

Please ensure to follow a good programming style and close/free all your message queues before your script exits to avoid those warning messages.

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pail dot luo at gmail dot com ¶

15 years ago


A simple Sample to introduce Message Queue. 

<?php 
if ( sizeof($argv)<2 ) { 
        echo "Usage: $argv[0] stat|send|receive|remove msgType MSG [msg] \n\n" ; 
        echo "   EX: $argv[0] send 1 \"This is no 1\" \n" ; 
        echo "       $argv[0] receive ID \n" ; 
        echo "       $argv[0] stat \n" ; 
        echo "       $argv[0] remove \n" ; 
        exit; 
} 

$MSGKey = "123456" ; 

## Create or attach to a message queue 
$seg = msg_get_queue($MSGKey) ; 

switch ( $argv[1] ) { 
    case "send": 
        msg_send($seg, $argv[2], $argv[3]); 
        echo "msg_send done...\n" ; 
        break; 
        
    case "receive": 
        $stat = msg_stat_queue( $seg ); 
        echo 'Messages in the queue: '.$stat['msg_qnum']."\n"; 
        if ( $stat['msg_qnum']>0 ) { 
            msg_receive($seg, $argv[2], $msgtype, 1024, $data); 
            var_dump($msgtype); 
            var_dump($data); 
            echo "\n"; 
        } 
        else { 
            echo "No Msg...\n"; 
        } 
        break; 
    
    case "stat": 
      print_r( msg_stat_queue($seg) ); 
        break; 
        
    case "remove": 
        msg_remove_queue($seg); 
        break; 
} 
?>

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Joey ¶

5 years ago


I find it hard to work out how to really use this reliably particularly in respect to collisions.

It maps to SysV IPC msgget.

As I see it you have three options...

1. Manage the IDs yourself, allocating various ranges or using some kind of centralised mechanism.
2. Use ftok. This attempts to find a unique ID, though it's not guaranteed to be unique or constant in absolutely every circumstance. It relies on using a file, from which it uses bits from the inode and dev it expects to be unique. It's the standard way and as long as there's nothing too unusual it should probably work (but might not survive radical FS changes).
3. Use 0 as the key, which appears to map to IPC_PRIVATE, a magic value which if provided as a key creates a new queue each time (without a key in effect).

Unfortunately option #3 is of limited use in PHP.

In C that is useful might be useful as the queue resource is just identified by an int and can be passed around.

In PHP its utility is questionable as only the resource can be passed within a single process. It's not possible to pass the resource with serialize / unserialize even though it's just a wrapped int.

The msqid returned isn't exactly unpredictable either so can quite easily be accidentally accessed. The first one I got was 0.

If you create a queue like this you'll find it very annoying as it wont be possible to delete it via PHP.

Like all IO it's worth wrapping this function and launching an exception if the input is 0.

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martin dot velek at gmail dot com ¶

17 years ago


Lack of IPC_EXCL makes me unhappy. Of course, you can use ftok() to generate a unique key. This code is not allmighty, another process under the same user can open the queue and function returns true. But in some situation it could help.

code:

<?
function ipcEXCL($res,$perm)
{
 $pole = msg_stat_queue($res);
 
 if($pole['msg_perm.uid']==posix_getuid() &&
    $pole['msg_perm.gid']==posix_getgid()  &&
    $pole['msg_perm.mode']==$perm  &&
    $pole['msg_stime']==0  &&
    $pole['msg_rtime']==0  &&
    $pole['msg_qnum']==0  &&
    $pole['msg_lspid']==0  &&
    $pole['msg_rspid']==0)
        return true;
 else
        return false;
}

$res=msg_get_queue($key,$perm);

if(ipcEXCL($res,$perm))
   echo "probably I am a creator:";
else
   echo "probably not";
?>

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-1

joeldg AT listbid.com ¶

21 years ago


// Here is an example of working with message queues.
// if you have forked processes, this could be a great way of passing
// out work to them

// create the message queue
// pick a file..
  $key_t = msg_get_queue(ftok("/tmp/php_msgqueue.stat", 'R'),0666 | IPC_CREAT);

    // place two messages on the queue
    if (!msg_send ($key_t, 1, 'This is message #1', true, true, $msg_err))
       echo "Msg not sent because $msg_err\n";
    if (!msg_send ($key_t, 1, 'This is message #2 ', true, true, $msg_err))
       echo "Msg not sent because $msg_err\n";
      
    // lets look at the queue structure 'msg_qnum' is really what we want to see
    // it should be '2'
    print_r(msg_stat_queue($key_t));
    
    // pull off the stack
        if (msg_receive ($key_t, 1, $msg_type, 16384, $msg, true, 0, $msg_error)) {
           if ($msg == 'Quit');
           echo "$msg\n"; // prints 'This is message #1'
        } else {
           echo "Received $msg_error fetching message\n";
        }
    // look at the structure again, ms_qnum should be '1'    
    print_r(msg_stat_queue($key_t));
        if (msg_receive ($key_t, 1, $msg_type, 16384, $msg, true, 0, $msg_error)) {
           if ($msg == 'Quit');
           echo "$msg\n"; // prints 'This is message #2'
        } else {
           echo "Received $msg_error fetching message\n";
        }
   // look at the structure again, ms_qnum should be '0', no more messages on the queue
   print_r(msg_stat_queue($key_t));  

   // get rid of the queue we created
   msg_remove_queue ($key_t);

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-5

Morten Brrup ¶

14 years ago


IPC_CREAT has no effect in this function. The PHP source code (file sysvmsg.c) reveals that only if msgget(key,0) fails, msgget(key, IPC_CREAT | IPC_EXCL | perms) is used.

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