Please help:program hang stuck there signal handling on POSIX Message Queue UNIX C programming


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Top Forums Programming Please help:program hang stuck there signal handling on POSIX Message Queue UNIX C programming
# 1  
Java help:wrong behavior code:client-server IPC signal handling on POSIX Message Queue UNIX C programming

in a single main() function,so need signal handling. Use Posix Message Queue IPC mechanism , can ignore the priority and other linked list message,to implement the scenario:

client:Knock Knock
server:who's there
client: Eric
Server:Eric,Welcome.
client:exit
all process terminated

stdin->POSIX MsgQ client send "knock knock" to server->Server compares string and send "who's there" back to client

Below is my code,

What I got is :
client:knock knock
Server:Who's there?
client:eric
eric
client:Exit
Exit


1st round succeed get the right result.From 2nd round, the client put the same typing on console.
Please help. Remember to use gcc -lrt to link mq_function.


Code:
#include <mqueue.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>
#include <string.h>
#define MSG_SIZE 100  //max size of msg
#define MAX_MSG 1  //max # of msg
#define FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
static void sig_usr1(int signo) {
    mqflag = 1;
    sigprocmask(SIG_BLOCK, &newmask, &oldmask);
    return;
}


Last edited by ouou; 07-09-2011 at 09:00 PM.. Reason: How to get right indention when place code?
# 2  
I strongly advise you to check the return code by the system calls. That way, you'll catch early error like invalid mq descriptor caused by a failed mq_open.

HTH, Loc
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