LinuxQuestions.org
Download your favorite Linux distribution at LQ ISO.
Go Back   LinuxQuestions.org > Forums > Non-*NIX Forums > Programming
User Name
Password
Programming This forum is for all programming questions.
The question does not have to be directly related to Linux and any language is fair game.

Notices



Reply
 
Search this Thread
Old 10-18-2004, 05:54 PM   #1
feetyouwell
Member
 
Registered: Dec 2003
Location: NC, US
Distribution: Novell Linux Eval (2.6.5)
Posts: 240

Rep: Reputation: 30
programming for message queue and such ...


I am writing a practise for using message queue in linux, there are a few mistries i can't seem to figure out. code are posted after this
i have two programs, ./server and ./client, when I do ./client <cmd>, ./client supposes to send the <cmd> to the queue and server will retrieve it, exec it and send the results back to the queue and client gets it, display it and quit.
when I do one ./client <cmd> and then do ipcs, it shows me there is no messages
i open another terminal and do it again, it shows me there is one message
i open another terminal and do it again, it shows me there is 2 messages
and so on, why the first one didn't get added to the queue, that's my biggest question right now
queue struct
Code:
const long int  SERVER = 1L;    //msg type for server
                                                                                                                             
typedef struct {
        long int msg_to;
        long int msg_fm;
        char buffer[BUFSIZ];
} MESSAGE;
[code]
client code
Code:
#include "local.h"
#include <stdio.h>

int main (int argc, char *argv[]) {
	pid_t c_pid;
	int mid, n=0, i, pos =0;
	char *pch;
	MESSAGE msg;
	bzero(msg.buffer, BUFSIZ);
	c_pid = getpid();
	
	if ((mid=msgget(2,IPC_CREAT)) == -1) {
		perror ("Server is not running");
		return 1;
	}
printf("mid is %d\n", mid);
	while (1) {
		msg.msg_to = SERVER;
		msg.msg_fm = c_pid;
		memset(msg.buffer, 0x0, BUFSIZ);
		for(i=0; i<argc; i++) {
			strcat(msg.buffer, argv[i]);
			strcat(msg.buffer, " ");
printf("argv[%i] is %s and n is %d and str is %s and size %d\n", i, argv[i], n, msg.buffer, sizeof(msg.buffer));	
		}	
		n = sizeof(char) * strlen(msg.buffer);
		n += sizeof(msg.msg_fm);
printf("n is %d\n", n);

		if(msgsnd(mid, &msg, n, 0) == -1) {
			perror ("Client: msgsnd");
			return 3;
		}
		if ( (n=msgrcv(mid, &msg, BUFSIZ, c_pid, 0)) != -1 ) {
			printf("Client MSQID: %d\n", c_pid);
			write(fileno(stdout), msg.buffer, n);
			break;
		}
	}
	printf("Client exit\n");
	return 0;
}
server code
Code:
#include "local.h"
#include <signal.h>
#include <fcntl.h>

int smid;
MESSAGE msg;
void server_cmd();
void sig_catch_u1(int);

int main (int argc, char *argv[]) {
	int n,t=0;
	FILE *fp;	
	
	signal(SIGUSR1, sig_catch_u1);

	if ((smid=msgget(2, 0)) == -1) {
		smid = msgget(2, IPC_CREAT | IPC_EXCL | 0660);		//create msg queue
	}
	while (1) {
		memset(msg.buffer, 0x0, BUFSIZ);
		if ((n=msgrcv(smid, &msg, BUFSIZ, SERVER, 0)) == -1) {
			perror("Server: msgrcv");
			return 2;
		}
		else if (n == 0) {
			break;
		}
printf("server: get here and n is %d\n", n);
printf("server: msg.buffer is %s\n", msg.buffer);

		switch(fork()) {
			case -1:
				perror("Fork error");
				exit(1);
			case 0:
				server_cmd();
		}

printf("server: after fork\n");

		if ((fp = fopen("/tmp/server_tmp", "r")) == NULL) {	
			perror("Open file error");
			exit(1);
		}

		do {
			msg.buffer[t++] = getc(fp);
		}while(msg.buffer[t] != EOF || t>= BUFSIZ);

		msg.msg_to = msg.msg_fm;
		msg.msg_fm = SERVER;

		n = sizeof(char) * strlen(msg.buffer);
		n += sizeof(msg.msg_fm);
		
		if (msgsnd(smid, &msg, n, 0) == -1) {
			perror("Server: msgsnd");
			return 3;
		}	
	}	
}

void server_cmd() {
	char *s_cmd, *new_args[20];
	int s_fd, i=0;

	if ((s_fd=open("/tmp/server_tmp", O_WRONLY|O_CREAT|O_TRUNC, S_IRUSR|S_IWUSR))==-1) {
		perror ("Open error");
		exit(0);
	}
	if (dup2(s_fd, fileno(stdout)) == -1) {
		perror ("Dup2 erorr");
		exit(0);
	}
	
	s_cmd = msg.buffer;
	new_args[i] = strtok(s_cmd, " \t");
	while (*new_args[i] != '\0'){
		i++;
	}
	new_args[i] = NULL;
	
	execvp(new_args[1], &new_args[1]);
	perror("Execvp failure");
	exit(1);	
}

void sig_catch_u1 (int sig) 
{
	signal(sig, sig_catch_u1);
	msgctl(smid, IPC_RMID, (struct msqid_ds *) 0);		
	exit(0);
}
 
  


Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
does rh9.0 support POSIX message queue? simon_qwl Programming 1 07-22-2005 06:25 PM
multithreaded server using single message queue ekern Programming 0 11-19-2004 02:30 AM
Share programming code, Instant Message firefly2442 Programming 7 09-27-2004 12:42 AM
Qmail Message Queue dadepfan Linux - Software 0 07-22-2004 04:54 PM
Overfilled message queue. I need very ugent help! J_Szucs Linux - Software 2 05-23-2002 10:25 AM


All times are GMT -5. The time now is 09:43 AM.

Main Menu
Advertisement
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
identi.ca: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration