內容簡介

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

int msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg);

ssize_t msgrcv(int msqid, void *msgp, size_t msgsz, long msgtyp, int msgflg);

描述

The msgp argument is a pointer to caller-defined structure of the following general form:

struct msgbuf { 
	       long    mtype;   /* message type, must be > 0 */ 
	       char    mtext[1];        /* message data */ 
	  };

The mtext field is an array (or other structure) whose size is specified by msgsz, a non-negative integer value. Messages of zero length (i.e., no mtext field) are permitted. Themtype field must have a strictly positive integer value. This value can be used by the receiving process for message selection (see the description of msgrcv() below).

The msgsnd() system call appends a copy of the message pointed to by msgp to the message queue whose identifier is specified by msqid.

If sufficient space is available in the queue, msgsnd() succeeds immediately. (The queue capacity is defined by the msg_bytes field in the associated data structure for the message queue. During queue creation this field is initialised to MSGMNB bytes, but this limit can be modified using msgctl().) If insufficient space is available in the queue, then the default behaviour of msgsnd() is to block until space becomes available. IfIPC_NOWAIT is specified in msgflg, then the call instead fails with the error EAGAIN.

A blocked msgsnd() call may also fail if the queue is removed (in which case the system call fails with errno set to EIDRM), or a signal is caught (in which case the system call fails with errno set to EINTR). (msgsnd and msgrcv are never automatically restarted after being interrupted by a signal handler, regardless of the setting of theSA_RESTART flag when establishing a signal handler.)

在成功完成訊息佇列的資料結構更新如下：

RETURN VALUE

ERRORS

CONFORMING TO

NOTES

The following limits on message queue resources affect the msgsnd() call:

SEE ALSO

• msgctl (2)

• msgget (2)

• msgrcv (2)

• msgsnd (2)