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1、消息队列就是一个消息的链表。可以把消息看作一个记录,具有特定的格式以及特定的优先级
2、 对消息队列有写权限的进程可以向其中按照一定的规则添加新消息;对消息队列有读权限的进程则可以从消息队列中读走消息。
3、man 2 msgrcv
4、函数int msgget(key_t key, int msgflg)
–参数“key”:消息队列关联的标识符 key = IPC_PRIVATV = 0 –参数“msgflg”:消息队列的建立标志和存取权限。IPC_CREAT 如果内核中没有此队列则创建它;IPC_EXCL 当 和IPC_CREAT 一起使用时,如果队列已经存在,则失败。 –返回值:执行成功则返回消息队列的标识符,否则返回-1。
5、 #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h>
int msgctl(int msqid, int cmd, struct msqid_ds *buf); msqid:为指定的要操作的队列 cmd:参数指定所要进行的操作,其中有些操作需要buf参数。 IPC_STAT IPC_SET IPC_RMID //删除消息队列
struct msqid_ds { struct ipc_perm msg_perm; /* Ownership and permissions */ time_t msg_stime; /* Time of last msgsnd(2) */ time_t msg_rtime; /* Time of last msgrcv(2) */ time_t msg_ctime; /* Time of last change */ unsigned long __msg_cbytes; /* Current number of bytes in queue (nonstandard) */ msgqnum_t msg_qnum; /* Current number of messages in queue */ msglen_t msg_qbytes; /* Maximum number of bytes allowed in queue */ pid_t msg_lspid; /* PID of last msgsnd(2) */ pid_t msg_lrpid; /* PID of last msgrcv(2) */};The ipc_perm structure is defined as follows (the highlighted fields are settable using IPC_SET):struct ipc_perm { key_t __key; /* Key supplied to msgget(2) */ uid_t uid; /* Effective UID of owner */ gid_t gid; /* Effective GID of owner */ uid_t cuid; /* Effective UID of creator */ gid_t cgid; /* Effective GID of creator */ unsigned short mode; /* Permissions */ unsigned short __seq; /* Sequence number */};6、函数ssize_t msgrcv(int msqid, void *msgp, size_t msgsz, long msgtyp,int msgflg)
–参数msqid:消息队列的标识码
–参数*msgp:指向消息缓冲区的指针
–参数msgsz:消息的长短
–参数msgtyp
• msgtyp等于0 ,则返回队列的最早的一个消息
• msgtyp大于0,则返回其类型为mtype的第一个消息
• msgtyp小于0,则返回其类型小于或等于mtype参数的绝对值的最小的一个消息
–参数msgflg:标志位为0,则表示忽略
–返回值:成功返回数据长度,错误返回-1
7、函数int msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg)
–参数msqid:消息队列的标识码
–参数*msgp:指向消息缓冲区的指针,此位置用来暂时存储发送和接收的消息,是一个用户可定义的通用结构
–参数msgsz:消息的长短
–参数msgflg:标志位
–返回值:成功返回0,错误返回-1
结构体msgp,是一个标准的通用结构
struct msgbuf { long mtype; /* message type, must be > 0 */ char mtext[nbyte]; /* message data */};例:
msgsend.c
#include#include #include #include #include #include #define MAX_TEXT 512 struct msg_st { long int msg_type; char text[MAX_TEXT]; }; int main(){ int running = 1; struct msg_st data; char buffer[BUFSIZ]; int msgid = -1; //建立消息队列 msgid = msgget((key_t)1234, 0666 | IPC_CREAT); if(msgid == -1) { fprintf(stderr, "msgget failed with error: %d\n", errno); exit(EXIT_FAILURE); } //向消息队列中写消息,直到写入end while(running) { //输入数据 printf("Enter some text: "); fgets(buffer, BUFSIZ, stdin); data.msg_type = 1; //注意2 strcpy(data.text, buffer); //向队列发送数据 if(msgsnd(msgid, (void*)&data, MAX_TEXT, 0) == -1) { fprintf(stderr, "msgsnd failed\n"); exit(EXIT_FAILURE); } //输入end结束输入 if(strncmp(buffer, "end", 3) == 0) running = 0; sleep(1); } exit(EXIT_SUCCESS); }
msgreceive.c
#include#include #include #include #include #include struct msg_st{ long int msg_type; char text[BUFSIZ]; }; int main() { int running = 1; int msgid = -1; struct msg_st data; long int msgtype = 0; //注意1 //建立消息队列 msgid = msgget((key_t)1234, 0666 | IPC_CREAT); if(msgid == -1) { fprintf(stderr, "msgget failed with error: %d\n", errno); exit(EXIT_FAILURE); } //从队列中获取消息,直到遇到end消息为止 while(running) { if(msgrcv(msgid, (void*)&data, BUFSIZ, msgtype, 0) == -1) { fprintf(stderr, "msgrcv failed with errno: %d\n", errno); exit(EXIT_FAILURE); } printf("You wrote: %s\n",data.text); //遇到end结束 if(strncmp(data.text, "end", 3) == 0) running = 0; } //删除消息队列 if(msgctl(msgid, IPC_RMID, 0) == -1) { fprintf(stderr, "msgctl(IPC_RMID) failed\n"); exit(EXIT_FAILURE); } exit(EXIT_SUCCESS); }
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