进程间的通信-消息队列

1.创建或打开一个消息队列:

int msgget(key_t key,int flag);//#include<sys/msg.h>

成功则返回消息队列的id，否则返回-1;key是消息队列的外部名称，标识符是队列的内部名称.

2.每个消息队列都有一个msqid_ds结构与其相关，该结构规定了队列的当前状态。

struct msqid_ds {

struct ipc_perm msg_perm;

struct msg *msg_first; /* first message on queue */

struct msg *msg_last; /* last message in queue */

__kernel_time_t msg_stime; /* last msgsnd time */

__kernel_time_t msg_rtime; /* last msgrcv time */

__kernel_time_t msg_ctime; /* last change time */

struct wait_queue *wwait;

struct wait_queue *rwait;

unsigned short msg_cbytes; /* current number of bytes on queue */

unsigned short msg_qnum; /* number of messages in queue */

unsigned short msg_qbytes; /* max number of bytes on queue */

__kernel_ipc_pid_t msg_lspid; /* pid of last msgsnd */

__kernel_ipc_pid_t msg_lrpid; /* last receive pid */

};

3.int msgctl(int msqid,int cmd,struct msqid_ds *buf);////#include<sys/msg.h>

成功返回消息队列id，否则返回-1；该函数是对消息队列的操作。

4 int msgsnd(int msqid,const void *ptr,size_t nbytes,int flag);//#include<sys/msg.h>

返回值：成功0，失败-1，讲数据放到消息队列中

5.ssize_t msgsnd(int msqid,const void *ptr,size_t nbytes,int flag);//#include<sys/msg.h>

返回值：成功返回接收数据长度，失败-1，讲数据放到消息队列中