函数: key_t ftok(const char *filename, int proj_id);
通过文件名和项目号获得System V IPC键值(用于创建消息队列、共享内存所用)
proj_id:项目号,不为0即可
返回:成功则返回键值,失败则返回-1
函数: int msgget(key_t key, int msgflg);
key:键值,当为IPC_PRIVATE时新建一块共享内存;
shmflg:标志。
IPC_CREAT:内存不存在则新建,否则打开;
IPC_EXCL:只有在内存不存在时才创建,否则出错。
返回:成功则返回标识符,出错返回-1
函数: int msgsnd(int msgid, const void *msgp, size_t sz, int flg);
向消息队列发送消息
msgid:通过msgget获取
msgp:指向消息内容的指针
sz:消息内容的大小
flg:处理方式;如为IPC_NOWAIT时表示空间不足时不会阻塞
返回:成功则返回0,失败返回-1
函数: int msgrcv(int msgid, void *msgp, size_t sz, long type, int flg);
从消息队列读取消息
msgid:通过msgget获取
msgp:指向消息内容的指针
sz:消息内容的大小
type:指定接收的消息类型;若为0则队列第一条消息将被读取,而不管类型;若大于0则队列中同类型的消息将被读取,如在flg中设了MSG_RXCEPT位将读取指定类型的其他消息;若小于0读取绝对值小于type的消息。
flg:处理方式;
返回:成功返回收到消息长度,错误返回-1
函数: int msgctl(int msgid, int cmd, struct msgid_ds *buf);
msgid:通过msgget获取
cmd:控制命令,如下:
IPC_STAT:获取消息队列状态
IPC_SET:改变消息队列状态
IPC_RMID:删除消息队列
buf:结构体指针,用于存放消息队列状态
返回:成功返回与cmd相关的正数,错误返回-1
Client.c
#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <sys/stat.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> #define N 1024 #define Pathname "/tmp/xkeyideal" #define MODE IPC_CREAT|IPC_EXCL|0666 #define ID 27 #define SENDMSG 1 #define RECVMSG 2 struct msgbuf{ int type; int a; int b; char text[N]; }msg_rbuf,msg_sbuf; int main(){ key_t key; key = ftok(Pathname,ID); int msgid; msgid = msgget(key,MODE); if(msgid == -1){ printf("error"); exit(1); } while(1){ pid_t pid,pid_wait; pid = fork(); if(pid > 0){ pid_wait = waitpid(pid,NULL,0);//父进程等待子进程先执行 printf("Parent process recv msg,pid = %d\n",getpid()); msgrcv(msgid,&msg_rbuf,sizeof(msg_rbuf),SENDMSG,0); int a = msg_rbuf.a; int b = msg_rbuf.b; printf("color: Receive: %s, sum %d + %d = %d\n",msg_rbuf.text,a,b,a+b); }else if(pid == 0){ char str[N]; printf("Child process send msg, pid = %d\n",getpid()); printf("Please input msg info str ,a ,b\n"); scanf("%s %d %d",str,&msg_sbuf.a,&msg_sbuf.b); strcpy(msg_sbuf.text,str); msg_sbuf.type = RECVMSG; msgsnd(msgid,&msg_sbuf,sizeof(msg_sbuf),IPC_NOWAIT); exit(0); } } msgctl(msgid,IPC_RMID,NULL); exit(0); }
Server.c
#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/msg.h> #include <sys/ipc.h> #define N 1024 #define Pathname "/tmp/xkeyideal" #define MODE IPC_CREAT|IPC_EXCL|0666 #define ID 27 #define SENDMSG 1 #define RECVMSG 2 struct msgbuf{ int type; int a; int b; char text[N]; }msg_rbuf; struct msgbuf2{ int type; int a; int b; char text[N]; }msg_sbuf; int main(){ key_t key; key = ftok(Pathname,ID); int msgid; msgid = msgget(key,0);//这里和上面的有不同 if(msgid == -1){ perror("Msgqueue has exist"); exit(1); } while(1){ pid_t pid; pid = fork(); if(pid > 0){//parent wait(NULL); msg_sbuf.type = SENDMSG; char str[N]; printf("Please input info: name , a, b\n"); scanf("%s %d %d",str,&msg_sbuf.a,&msg_sbuf.b); strcpy(msg_sbuf.text,str); printf("Parent process send msg, pid = %d\n",getpid()); msgsnd(msgid, &msg_sbuf,sizeof(msg_sbuf),IPC_NOWAIT); }else if(pid == 0){ msgrcv(msgid,&msg_rbuf,sizeof(msg_rbuf),RECVMSG,0); printf("Child process recv msg, pid = %d\n",getpid()); printf("xkey: Receive: %s, sum %d + %d = %d \n",msg_rbuf.text,msg_rbuf.a,msg_rbuf.b,msg_rbuf.a+msg_rbuf.b); exit(1); } } msgctl(msgid,IPC_RMID,NULL); exit(0); }
先启动Client再启动Server
另:在终端输入ipcs -q能看到创建的消息队列,ipcrm -q <msgqid>能够手动删除该消息队列