msg_send()

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

Send a message to a message queue

说明

msg_send(resource $queue,int $msgtype, mixed $message[,bool $serialize= TRUE[,bool $blocking= TRUE[,int &$errorcode]]]): bool

msg_send() sends a$messageof type$msgtype(which MUST be greater than 0)to the message queue specified by$queue.

参数

$queue: Message queue resource handle
$msgtype: The type of the message(MUST be greater than 0)
$message: The body of the message.
Note:
If$serializeset to FALSE is supplied, MUST be of type:string,integer,float or bool. In other case a warning will be issued.
$serialize: The optional$serializecontrols how the$messageis sent.$serializedefaults to TRUE which means that the$messageis serialized using the same mechanism as the session module before being sent to the queue. This allows complex arrays and objects to be sent to other PHP scripts, or if you are using the WDDX serializer, to any WDDX compatible client.
$blocking: If the message is too large to fit in the queue, your script will wait until another process reads messages from the queue and frees enough space for your message to be sent. This is called blocking; you can prevent blocking by setting the optional$blockingparameter to FALSE, in which case msg_send() will immediately return FALSE if the message is too big for the queue, and set the optional$errorcodeto MSG_EAGAIN, indicating that you should try to send your message again a little later on.
$errorcode: If the function fails, the optional errorcode will be set to the value of the system errno variable.

返回值

成功时返回TRUE，或者在失败时返回FALSE。

Upon successful completion the message queue data structure is updated as follows:$msg_lspidis set to the process-ID of the calling process,$msg_qnumis incremented by 1 and$msg_stimeis set to the current time.

参见

msg_remove_queue()Destroy a message queue
msg_receive()Receive a message from 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

I created example how to comunnicate with programe written in C throught messages queues. First run C program (it will create queue) then PHP script.
C code compile with: gcc -std=c99 -o test_queue test_queue.c
test_queue.c:
/**
* Example how to use System V Messages Queues with PHP and C program.
* This is simple server which create message queue and receive message from it.
* Based on Beej's Guide to Unix IPC
* Autor: Jan Drazil, <qeekin at gmail dot com>
*/
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
/* Buffer struct for receiving messages */
struct php_buf {
  long mtype;
  char msg[200];
};
int main(void)
{
  struct php_buf buf;
  int msqid;
  key_t key;
  /* Generate key (/var/www/index.php must be accessible file) */
  if((key = ftok("/var/www/index.php", 'G')) == -1) {
    perror("ftok");
    exit(EXIT_FAILURE);
  }
  /* Create message queue */
  if((msqid = msgget(key, 0666 | IPC_CREAT)) == -1) {
    perror("msgget");
    exit(EXIT_FAILURE);
  }
  printf("Ready to get string from PHP!\n");
  /* Receive message */
  if(msgrcv(msqid, &buf, sizeof(buf.msg)-1, 0, 0) == -1) {
    perror("msgrcv");
    exit(EXIT_FAILURE);
  }
  /* Eliminate segmentation fault */
  buf.msg[199] = '\0';
  printf("Recieved from PHP: %s\n", buf.msg);
  /* Destroy message queue */
  if(msgctl(msqid, IPC_RMID, NULL) == -1) {
    perror("msgctl");
    exit(EXIT_FAILURE);
  }
  return EXIT_SUCCESS;
}
test_queue.php:
<?php
/**
* Example how to use System V Messages Queues with PHP and C program.
* This is simple server which create message queue and receive message from it.
* Based on Beej's Guide to Unix IPC
* Autor: Jan Drazil, <qeekin at gmail dot com>
*/
/* Generate key, param fot ftok must be same as in test_msg.c */
if(($key = ftok("/var/www/index.php", "G")) == -1)
  die("ftok");
if(!msg_queue_exists($key))
  die("message queue doesn't exists");
/* Connect to message queue */
if(($msqid = msg_get_queue($key)) === FALSE)
  die("msg_get_queue");
echo "Sending text to msg queue.\n";
/* Send message to C program */
if(!msg_send($msqid, 12, "Hello from PHP!\0", false))
  die("msg_send");
echo "Done"
?>

When sending non-complex (serialize = false) messages to a program in C, you need to add the null character to the string (\0). Otherwise the previous message will be partially visible if it is longer than the current message. Took some kind help from comp.lang.php for me to figure that out. While it seems so obvious now, I thought I'd share it here.

$msgtype used in msg_send function can be any positive integer.

After about an hour of debugging I've discovered the meaning of the undocumented "PHP Warning: msg_send(): msgsnd failed: Invalid argument" ($errorcode = 13).
This occurred when the size of $message was larger than msg_qbytes (see msg_stat_queue() for how to determine and change msg_qbytes).

I think it is kinda lame why I cannot find out (easily) explicitly which types of messages are allowed and which ones are not. Maybe we can start our own little list. I know that strings work, and arrays do not.

Sample sending webpage, see msg_receive for matching service
<?php
  $MSGKEY = 519051;
  $msg_id = msg_get_queue ($MSGKEY, 0600);
  if (!msg_send ($msg_id, 1, 'Hi', true, true, $msg_err))
    echo "Msg not sent because $msg_err\n";
?>