10-10.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 <signal.h>

#if defined_GNU_LIBRARY_) && !defined(_SEM_SEMUN_UNDEFINED)
/* union semun is defined by including <sys/sem.h> */
#else
/* according to X/OPEN we have to define it ourselves */
union semun {
      int val;                  /* value for SETVAL */
      struct semid_ds *buf;     /* buffer for IPC_STAT, IPC_SET */
      unsigned short *array;    /* array for GETALL, SETALL */
                                /* Linux specific part: */
      struct seminfo *_buf;    /* buffer for IPC_INFO */
};
#endif

#define PROJID 0xFF
int semid;

void terminate_handler(int signo)
{
	semctl(semid, 0, IPC_RMID);
	exit(0);
}

int main(void)
{
	char filenm[] = "shared-file";
	char zero_blk[4096];
	char * mmap_addr;
	int fd;
	key_t semkey;
	struct sembuf getsem, setsem;
	union semun seminit;
	int ret;

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

	semid = semget(semkey, 2, IPC_CREAT | IPC_EXCL | 0666);
	if (semid == －1) {
		perror("semget error: ");
		exit(－1);
	}
	seminit.val = 0;
	semctl(semid, 0, SETVAL, seminit);
	semctl(semid, 1, SETVAL, seminit);

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

	setsem.sem_num = 0;
        setsem.sem_op = 1;
        setsem.sem_flg = SEM_UNDO;

	signal(SIGINT, terminate_handler);
	signal(SIGTERM, terminate_handler);

	memset(zero_blk, 0, 4096);
	fd = open(filenm, O_RDWR | O_CREAT);
        if (fd == －1) {
		perror("open error: ");
		semctl(semid, 0, IPC_RMID);
		exit(－1);
	}
	write(fd, zero_blk, 4096);
	mmap_addr = (char *)mmap(0, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
	if (mmap_addr == (char *)－1) {
		perror("mmap error: ");
		semctl(semid, 0, IPC_RMID);
		close(fd);
		exit(－1);
	}

	while (1) {
		printf("Lucy: ");
		fgets(mmap_addr, 256, stdin);
		if (strncmp("quit", mmap_addr, 4) == 0) {
			if (munmap(mmap_addr, 4096) == －1) {
				perror("munmap error: ");
			}
			close(fd);
			semctl(semid, 0, IPC_RMID);
			exit(0);
		}
		mmap_addr[strlen(mmap_addr)－1] = '\0';
		ret = semop(semid, &setsem, 1);
		if (ret == －1) {
			perror("semop error: ");
		}
		ret = semop(semid, &getsem, 1);
		if (ret == －1) {
			perror("semop error: ");
		}
		printf("Peter: %s\n", mmap_addr);
	}
		
}