信號(hào)量(Semphore)

#include <stdio.h>#include <unistd.h>#include <sys/types.h>#include <fcntl.h>#include <stdlib.h>#include <string.h>#include <sys/sem.h>union semun{	int val;	struct semid_ds *buf;	unsigned short *arry;};static int sem_id = 0;static int set_semvalue();static void del_semvalue();static int semaphore_p();static int semaphore_v();int main(int argc, char *argv[]) {	char message = 'X';	int i = 0;	// 創(chuàng)建信號(hào)量	sem_id = semget((key_t)1234, 1, 0666|ipC_CREAT);	if (argc > 1)	{		// 程序第一次被調(diào)用，初始化信號(hào)量		if (!set_semvalue())		{			fPRintf(stderr, "Failed to initialize semaphore./n");			exit(EXIT_FAILURE);		}		// 設(shè)置要輸出到屏幕中的信息，及其參數(shù)的第一個(gè)字符		message = argv[1][0];	}	for (i = 0; i < 10; ++i)	{		// 進(jìn)入臨界區(qū)		if (!semaphore_p())			exit(EXIT_FAILURE);		// 向屏幕中輸出數(shù)據(jù)		printf("%c", message);		// 清理緩沖區(qū)，然后休眠隨機(jī)時(shí)間		fflush(stdout);		sleep(rand() % 3);		// 離開臨界區(qū)前再次向屏幕輸出數(shù)據(jù)		printf("%c  ", message);		fflush(stdout);		// 離開臨界區(qū)，休眠隨機(jī)時(shí)間后繼續(xù)循環(huán)		if (!semaphore_v())			exit(EXIT_FAILURE);		sleep(rand() % 2);	}	sleep(10);	printf("/n%d finished./n", getpid());	if (argc > 1)	{		// 如果程序是第一次被調(diào)用，則在推出前刪除信號(hào)量		sleep(3);		del_semvalue();	}	exit(EXIT_SUCCESS);}static int set_semvalue(){	// 用于初始化信號(hào)量，在使用信號(hào)量前必須這樣做	union semun sem_union;	sem_union.val = 1;	if (semctl(sem_id, 0, SETVAL, sem_union) == -1)		return 0;	return 1;}static void del_semvalue(){	// 刪除信號(hào)量	union semun sem_union;	if (semctl(sem_id, 0, IPC_RMID, sem_union) == -1)		fprintf(stderr, "Failed to delete semaphore./n");}static int semaphore_p(){	// 對(duì)信號(hào)量做減１操作，即等待P(sv)	struct sembuf sem_b;	sem_b.sem_num = 0;	sem_b.sem_op = -1; // p()	sem_b.sem_flg = SEM_UNDO;	if (semop(sem_id, &sem_b, 1) == -1) {		fprintf(stderr, "semaphore_p failed./n");		return 0;	}	return 1;}static int semaphore_v(){	// 釋放操作，使信號(hào)量變?yōu)榭捎茫窗l(fā)送信號(hào)V(sv)	struct sembuf sem_b;	sem_b.sem_num = 0;	sem_b.sem_op = 1; // V()	sem_b.sem_flg = SEM_UNDO;	if (semop(sem_id, &sem_b, 1) == -1)	{		fprintf(stderr, "semaphore_v failed./n");		return 0;	}	return 1;}