信号量

#include <unistd.h>

#include <stdlib.h>

#include <stdio.h>

#include <sys/sem.h>//包含信号量定义的头文件

//联合类型semun定义

union semun{

int val;

struct semid_ds *buf;

unsigned short *array;

};

//函数声明

//函数：设置信号量的值

static int set_semvalue(int);

//函数：删除信号量

static void del_semvalue(void);

//函数：信号量P操作

static int semaphore_p(void);

//函数：信号量V操作

static int semaphore_v(void);

static int get_semvalue(void);

static int sem_id;//信号量ID

int main(int argc,char *argv[])

{

int i,val;

//创建一个新的信号量或者是取得一个已有信号量的键

sem_id = semget((key_t)1234,1,0666 | IPC_CREAT);

val=get_semvalue();

printf("val=%d\n",val);

set_semvalue(5);

val=get_semvalue();

printf("val2=%d\n",val);

semaphore_p();

val=get_semvalue();

printf("val3=%d\n",val);

//V操作，尝试离开缓冲区

semaphore_v();

val=get_semvalue();

printf("val4=%d\n",val);

printf("\n %d - finished \n",getpid());

}

//函数：设置信号量的值

static int set_semvalue(int val)

{

union semun sem_union;

sem_union.val = val;

if(semctl(sem_id,0,SETVAL,sem_union))

return 0;

return 1;

}

//获取信号量的值

static int get_semvalue(void)

{

int ret=semctl(sem_id,0,GETVAL);

return ret;

}

//函数：删除信号量

static void del_semvalue(void)

{

union semun sem_union;

if(semctl(sem_id,0,IPC_RMID,sem_union))

fprintf(stderr,"Failed to delete semaphore\n");

}

//函数：信号量P操作：对信号量进行减一操作

static int semaphore_p(void)

{

struct sembuf sem_b;

sem_b.sem_num = 0;//信号量编号

sem_b.sem_op = -1;//P操作

sem_b.sem_flg = SEM_UNDO;

if(semop(sem_id,&sem_b,1) == -1)

{

fprintf(stderr,"semaphore_p failed\n");

return 0;

}

return 1;

}

//函数：信号量V操作：对信号量进行加一操作

static int semaphore_v(void)

{

struct sembuf sem_b;

sem_b.sem_num = 0;//信号量编号

sem_b.sem_op = 1;//V操作

sem_b.sem_flg = SEM_UNDO;

if(semop(sem_id,&sem_b,1) == -1)

{

fprintf(stderr,"semaphore_v failed\n");

return 0;

}

return 1;

}