server2.c

让你了解Unix进程间的通信是如何实现的

#include	"cliserv2.h"

int
main(int argc, char **argv)
{
	int		fd, index, lastnoverflow, temp;
	long	offset;
	struct shmstruct	*ptr;

	if (argc != 2)
		err_quit("usage: server2 <name>");

		/* 4create shm, set its size, map it, close descriptor */
	shm_unlink(Px_ipc_name(argv[1]));		/* OK if this fails */
	fd = Shm_open(Px_ipc_name(argv[1]), O_RDWR | O_CREAT | O_EXCL, FILE_MODE);
	ptr = Mmap(NULL, sizeof(struct shmstruct), PROT_READ | PROT_WRITE,
			   MAP_SHARED, fd, 0);
	Ftruncate(fd, sizeof(struct shmstruct));
	Close(fd);

		/* 4initialize the array of offsets */
	for (index = 0; index < NMESG; index++)
		ptr->msgoff[index] = index * MESGSIZE;

		/* 4initialize the semaphores in shared memory */
	Sem_init(&ptr->mutex, 1, 1);
	Sem_init(&ptr->nempty, 1, NMESG);
	Sem_init(&ptr->nstored, 1, 0);
	Sem_init(&ptr->noverflowmutex, 1, 1);

		/* 4this program is the consumer */
	index = 0;
	lastnoverflow = 0;
	for ( ; ; ) {
		Sem_wait(&ptr->nstored);
		Sem_wait(&ptr->mutex);
		offset = ptr->msgoff[index];
		printf("index = %d: %s\n", index, &ptr->msgdata[offset]);
		if (++index >= NMESG)
			index = 0;				/* circular buffer */
		Sem_post(&ptr->mutex);
		Sem_post(&ptr->nempty);

		Sem_wait(&ptr->noverflowmutex);
		temp = ptr->noverflow;		/* don't printf while mutex held */
		Sem_post(&ptr->noverflowmutex);
		if (temp != lastnoverflow) {
			printf("noverflow = %d\n", temp);
			lastnoverflow = temp;
		}
	}

	exit(0);
}