Unix/Linux 进程间通信之消息队列应用实例

场景：

    进程A向消息队列写消息，而进程B则从消息队列读消息。

消息队列和之前的管道不同，消息队列是相对独立于进程的，它不需要进程自己来提供同步方法。消息队列里面有消息就可以读。

读取消息实例：msg_rcv.c

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

struct  my_msg_st {
    long int my_msg_type;
    char some_text[BUFSIZ];
};

int main(int argc,char **argv)
{
    int running = 1;
    int msgid;
    struct  my_msg_st some_data;
    long int msg_to_receive = 0;

    msgid = msgget((key_t)1234,0666 | IPC_CREAT);
    if(msgid == -1){
        fprintf(stderr,"Msgget failed!\n");
        exit(-1);
    }

    while(running){
        if(msgrcv(msgid,(void *)&some_data,BUFSIZ,msg_to_receive,0) == -1){
            fprintf(stderr,"Msgrcv failed!\n");
            exit(-1);
        }
        printf("You wrote: %s",some_data.some_text);
        if(strncmp(some_data.some_text,"end",3) == 0){
            running = 0;
        }
    }

    if(msgctl(msgid,IPC_RMID,0) == -1){
        fprintf(stderr,"Msgctl failed!\n");
        exit(-1);
    }

    exit(0);
}

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

struct	my_msg_st {
	long int my_msg_type;
	char some_text[BUFSIZ];
};

int main(int argc,char **argv)
{
	int	running = 1;
	int	msgid;
	struct	my_msg_st some_data;
	long int msg_to_receive = 0;

	msgid = msgget((key_t)1234,0666 | IPC_CREAT);
	if(msgid == -1){
		fprintf(stderr,"Msgget failed!\n");
		exit(-1);
	}

	while(running){
		if(msgrcv(msgid,(void *)&some_data,BUFSIZ,msg_to_receive,0) == -1){
			fprintf(stderr,"Msgrcv failed!\n");
			exit(-1);
		}
		printf("You wrote: %s",some_data.some_text);
		if(strncmp(some_data.some_text,"end",3) == 0){
			running = 0;
		}
	}

	if(msgctl(msgid,IPC_RMID,0) == -1){
		fprintf(stderr,"Msgctl failed!\n");
		exit(-1);
	}

	exit(0);
}

写入消息队列应用：msg_snd.c

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

#define MAX_TEXT    256

struct  my_msg_st {
    long int my_msg_type;
    char some_text[BUFSIZ];
};

int main(int argc,char **argv)
{
    int running = 1;
    int msgid;
    struct  my_msg_st some_data;
    char    buffer[BUFSIZ];

    msgid = msgget((key_t)1234,0666 | IPC_CREAT);
    if(msgid == -1){
        fprintf(stderr,"Msgget failed!\n");
        exit(-1);
    }

    while(running){
        printf("Enter Some Text: ");
        fgets(buffer,BUFSIZ,stdin);
        some_data.my_msg_type = 1;
        strcpy(some_data.some_text,buffer);
        if(msgsnd(msgid,(void *)&some_data,MAX_TEXT,0) == -1){
            fprintf(stderr,"Msgsnd failed!\n");
            exit(-1);
        }
        if(strncmp(some_data.some_text,"end",3) == 0){
            running = 0;
        }
    }
    exit(0);
}

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

#define	MAX_TEXT	256

struct	my_msg_st {
	long int my_msg_type;
	char some_text[BUFSIZ];
};

int main(int argc,char **argv)
{
	int	running = 1;
	int	msgid;
	struct	my_msg_st some_data;
	char	buffer[BUFSIZ];

	msgid = msgget((key_t)1234,0666 | IPC_CREAT);
	if(msgid == -1){
		fprintf(stderr,"Msgget failed!\n");
		exit(-1);
	}

	while(running){
		printf("Enter Some Text: ");
		fgets(buffer,BUFSIZ,stdin);
		some_data.my_msg_type = 1;
		strcpy(some_data.some_text,buffer);
		if(msgsnd(msgid,(void *)&some_data,MAX_TEXT,0) == -1){
			fprintf(stderr,"Msgsnd failed!\n");
			exit(-1);
		}
		if(strncmp(some_data.some_text,"end",3) == 0){
			running = 0;
		}
	}
	exit(0);
}

注意，这个程序的验证并不需要两个进程同时运行。

首先运行snd进程，写入几条消息。

然后启动rcv进程，读取消息并显示，最后删除消息队列文件。

备注：查看系统进程的IPC资源命令

# ipcs      //查看ipc资源

# ipcrm   //删除ipc资源