Linux下进程之间信号量互斥、同步

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一、信号量

信号量一般的作用就是用在进程之间的互斥和同步操作，跟线程的锁机制差不多的作用。线程当然也可以使用信号量来进行互斥、同步。

二、程序示例

/*commom.h*/#ifndef _COMMOM_H_#define _COMMOM_H_#include <sys/ipc.h>#include <sys/sem.h>#include <sys/types.h>#include <unistd.h>union semun{int val;struct semid_ds *buf;unsigned short *array;};int init_sem(int semid){union semun sem;sem.val = 1;if (semctl(semid, 0, SETVAL, sem)==-1){printf("set_sem failed!\n");exit(1);}return 0;}int del_sem(int semid){union semun sem;if (semctl(semid, 0, IPC_RMID, sem)==-1){printf("del_sem failed!\n");exit(1);}return 0;}int create_sem(key_t key, int num_sems){int semid;semid = semget(key, num_sems, 0666|IPC_CREAT);if (semid == -1){printf("create_sem failed!\n");exit(1);}return semid;}int sem_p(int semid){struct sembuf sem_buf;sem_buf.sem_num = 0;sem_buf.sem_op = -1;sem_buf.sem_flg = SEM_UNDO;if (semop(semid, &sem_buf, 1)==-1){printf("sem_p failed!\n");exit(1);}return 0;}int sem_v(int semid){struct sembuf sem_buf;sem_buf.sem_num = 0;sem_buf.sem_op = +1;sem_buf.sem_flg = SEM_UNDO;if (semop(semid, &sem_buf, 1)==-1){printf("sem_p failed!\n");exit(1);}return 0;}#endif

/*sem_write1.c*/#include <stdio.h>#include <stdlib.h>#include "commom.h"int main(void){FILE *fp;key_t key;int semid;key = ftok("./commom.h", 0);printf("0x%x\n", key);semid = create_sem(key, 1);fp = fopen("./text.txt", "a+");sem_p(semid);fwrite("english\n", 8, 1, fp);sem_v(semid);sleep(5);sem_p(semid);fwrite("test\n", 5, 1, fp);sem_v(semid);sleep(5);fclose(fp);del_sem(semid);return 0;}

/*sem_write2.c*/#include <stdio.h>#include <stdlib.h>#include "commom.h"int main(void){int semid;key_t key;FILE *fp;fp = fopen("./text.txt", "a+");key = ftok("./commom.h", 0);printf("0x%x\n", key);semid = create_sem(key, 1);init_sem(semid);sem_p(semid);fwrite("hello\n", 6, 1, fp);sem_v(semid);sleep(5);sem_p(semid);fwrite("world\n", 6, 1, fp);sem_v(semid);fclose(fp);return 0;}

#makefileCFLAGS = -Wall -gCC = gccTARGET = sem_write1 sem_write2all:$(TARGET)sem_write1:sem_write1.o$(CC) $(CFLAGS) -o $@ $^sem_write2:sem_write2.o$(CC) $(CFLAGS) -o $@ $^%.o:%.c %.h$(CC) -c -o $@ $<clean:rm -f $(TARGET) *.o

注意：先运行sem_write2，因为sem_write2有对信号量进行初始化的操作，然后才能进行P/V操作。

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