POSIX Message Queuing for Unix IPC (1)

Section reference: http://www.cnblogs.com/Anker/archive/2013/01/04/2843832.html

The persistence of IPC objects: http://book.51cto.com/art/201006/207275.htm

Message Queuing can be thought of as a list of messages that, before a process writes a message to a message queue, does not require another process to wait for the message to arrive on that queue, as opposed to a pipeline and a FIFO. The differences between POSIX Message Queuing and System V Message Queuing are as follows:

1. The read of POSIX Message Queuing always returns the oldest message with the highest priority, and the read of System V Message Queuing can return messages of any given priority.
2. When a message is placed into an empty queue, POSIX Message Queuing allows a signal to be generated or a thread to start, and System V Message Queuing does not provide a similar mechanism.

The POSIX Message Queuing operation functions are as follows:

header files and some definitions:

#include    <mqueue.h>int mqd_t;

/*establish connection between a process and a message queue NAME and return message Queue descriptor or (mqd_t)-1 o  N error.  OFLAG determines the type of access used.    If O_creat is on OFLAG, the third argument is taken as a ' mode_t ', the mode of the created message queue, and the fourth  argument is taken as ' struct mq_attr * ', pointer to message queue attributes.  If The fourth argument is NULL, the default attributes is used. */externmqd_t Mq_open (__constChar*__name,int__oflag, ...) __throw __nonnull ((1));/*removes the association between message Queue descriptor Mqdes and its message queue. */extern intmq_close (mqd_t __mqdes) __throw;/*Remove Message Queue named NAME. */extern intMq_unlink (__constChar*__name) __throw __nonnull (1));

The following function is used to write the program process test.

Program 1 (mqcreate1.c): Creates a message queue whose name is specified as a command-line argument. The procedure is as follows:

#include"unpipc.h"intMain (intargcChar**argv) {    intC, flags; mqd_t MQD; //under Linux is the int typeFlags= O_rdwr |o_creat;  while(c = Getopt (argc, argv,"e")) != -1)    {        Switch(c) { Case 'e': Flags|=o_excl;  Break; }    }    if(Optind! = argc-1) Err_quit ("Usage:mqcreate [-e] <name>"); MQD=Mq_open (Argv[optind], flags, File_mode, NULL);    Mq_close (MQD); Exit (0);}

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Program 2 (MQUNLINK.C): Deletes a message queue. The procedure is as follows:

#include    "unpipc.h"intmain (intChar * *  argv) {    if2)        err_quit ("usage:mqunlink <name >");    Mq_unlink (argv[1]);    Exit (0);}

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Note: The code needs to be compiled in the UNIX Network programming-Volume 2 package.

POSIX Message Queuing is built into the system's virtual file system and can be mounted to the system's file system for viewing;

The Mount command format is as follows:

The Mount command is as follows:

[[email protected] pxmsg]$ mkdir/tmp/-t mqueuenone/tmp/do-1  -T mqueue none/tmp/for

Program Run Result:

[Email protected] pxmsg]$/mqunlink/temp.1234[dell@localhost pxmsg]$ ls-l/tmp/mqueue/0[Dell @localhost pxmsg]$/mqcreate1/temp.1234[dell@localhost pxmsg]$ ls-l/tmp/mqueue/0-rw-r--r-- . 1 Dell Dell 80 August  20:10 temp.1234[Dell@localhost pxmsg]$./mqunlink/temp.1234[Dell@localhost pxmsg]$ ls-l/tmp/mqueue/0[Dell

Description: Why do you want to do this, run a command query under the shell:

Mans 7 Mq_overview

Here you select some of the documentation:

mounting the message queue file system        inch Virtual file system.   (Other       implementations  -  also  provide such a feature, but the details is       likely to differ.)  This file system can is mounted (by the  superuser)       using the following commands:           
    /dev/mqueue           -t mqueue none/dev/mqueueeach message  queueis  Identi fied by a name of the form/somename.  The processes can operate on thesame queue by passing the same name to Mq_open ().

POSIX Message Queuing for Unix IPC (1)