10-9.c

《Linux应用开发技术详解》附书光盘中的例程。

#include <stdio.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>

#define PROJID 0xFF
int main(void)
{
	char filenm[] = "shared-file";
	char * shm_addr;
	int semid, shmid;
	key_t semkey, shmkey;
	struct sembuf getsem, setsem;

	semkey = ftok(filenm, PROJID);
	if (semkey == －1) {
		perror("ftok error: ");
		exit(－1);
	}

	semid = semget(semkey, 0, 0);
	if (semid == －1) {
		perror("semget error: ");
		exit(－1);
	}

	getsem.sem_num = 0;
        getsem.sem_op = －1;
        getsem.sem_flg = SEM_UNDO;

	setsem.sem_num = 1;
        setsem.sem_op = 1;
        setsem.sem_flg = SEM_UNDO;

	shmkey = ftok(filenm, PROJID + 0x0F00);
        if (shmkey == －1) {
                perror("ftok error: ");
                exit(－1);
        }
                                                                                
        shmid = shmget(shmkey, 4096, 0);
        if (shmid == －1) {
                perror("shmget error: ");
                exit(－1);
        }
        shm_addr = (char *)shmat(shmid, NULL, 0);
        if (shm_addr == (char *)－1) {
                perror("shmat error: ");
                exit(－1);
        }

	while (1) {
		semop(semid, &getsem, 1);
		printf("Lucy: %s\n", shm_addr);
		printf("Peter: ");
		fgets(shm_addr, 256, stdin);
		if (strncmp("quit", shm_addr, 4) == 0) {
			shm_addr[strlen(shm_addr)－1] = '\0';
			semop(semid, &setsem, 1);
			if (shmdt(shm_addr) == －1) {
				perror("shmdt error: ");
			}
			exit(0);
		}
		shm_addr[strlen(shm_addr)－1] = '\0';
		semop(semid, &setsem, 1);
	}
		
}