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📄 svmsgread.c

📁 让你了解Unix进程间的通信是如何实现的
💻 C
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#include	"unpipc.h"#define	MAXMSG	(8192 + sizeof(long))intmain(int argc, char **argv){	int		pipe1[2], pipe2[2], mqid;	char	c;	pid_t	childpid;	fd_set	rset;	ssize_t	n, nread;	struct msgbuf	*buff;	if (argc != 2)		err_quit("usage: svmsgread <pathname>");	Pipe(pipe1);			/* 2-way communication with child */	Pipe(pipe2);	buff = My_shm(MAXMSG);	/* anonymous shared memory with child */	if ( (childpid = Fork()) == 0) {		Close(pipe1[1]);			/* child */		Close(pipe2[0]);		mqid = Msgget(Ftok(argv[1], 0), MSG_R);		for ( ; ; ) {				/* 4block, waiting for message, then tell parent */			nread = Msgrcv(mqid, buff, MAXMSG, 0, 0);			Write(pipe2[1], &nread, sizeof(ssize_t));				/* 4wait for parent to say shm is available */			if ( (n = Read(pipe1[0], &c, 1)) != 1)				err_quit("child: read on pipe returned %d", n);		}		exit(0);	}/* $$.bp$$ */		/* 4parent */	Close(pipe1[0]);	Close(pipe2[1]);	FD_ZERO(&rset);	FD_SET(pipe2[0], &rset);	for ( ; ; ) {		if ( (n = select(pipe2[0] + 1, &rset, NULL, NULL, NULL)) != 1)			err_sys("select returned %d", n);		if (FD_ISSET(pipe2[0], &rset)) {			n = Read(pipe2[0], &nread, sizeof(ssize_t));/* *INDENT-OFF* */			if (n != sizeof(ssize_t))				err_quit("parent: read on pipe returned %d", n);/* *INDENT-ON* */			printf("read %d bytes, type = %ld\n", nread, buff->mtype);			Write(pipe1[1], &c, 1);		} else			err_quit("pipe2[0] not ready");	}	Kill(childpid, SIGTERM);	exit(0);}

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