linux下的信号量操作示例

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <pthread.h>
#include <errno.h>
#include <vector>
#include <iostream>
using namespace std;

union semun {
int val; /* Value for SETVAL */
struct semid_ds *buf; /* Buffer for IPC_STAT, IPC_SET */
unsigned short *array; /* Array for GETALL, SETALL */
struct seminfo *__buf; /* Buffer for IPC_INFO
(Linux specific) */
};

//工作线程函数
void * workproc(void * param)
{
int sid = *(int *)param; //信号量ID
pthread_t tid = pthread_self(); //线程ID

cout <<"thread " <<tid <<"/t opt 1 is ok!" <<endl; //第一步操作执行完成

//信号量减1
sembuf b;
b.sem_num = 0;
b.sem_op = -1;
b.sem_flg = 0;
int ret = semop(sid, &b, 1);
if (ret != 0)
return (void *)-1;

//等待信号量变成0
cout <<"thread " <<tid <<"/t begin wait for all thread ok!" <<endl;
b.sem_op = 0;
ret = semop(sid, &b, 1);
if (ret != 0)
return (void *)-1;
cout <<"thread " <<tid <<"/t end wait for all thread ok!" <<endl;

//执行第二步操作
cout <<"thread " <<tid <<"/t opt 2 is ok!" <<endl;

return 0;
}

int main()
{
//创建信号量
int sid = semget(IPC_PRIVATE, 1, IPC_CREAT|0660);
if (sid == -1)
{
cout <<"create sem error!" <<endl;
return -1;
}

//设置信号量的初始值为5
semun un;
un.val = 5;
int ret = semctl(sid, 0, SETVAL, un);
if (ret == -1)
return -1;

//启动一组工作线程
vector<pthread_t> ids; //保存启动的线程ID数组
pthread_t id;
for (int i = 0; i < 5; ++i)
{
pthread_create(&id, NULL, workproc, &sid);
ids.push_back(id);
}

//等待所有的工作线程结束
int num = ids.size();
for (int i = 0; i < num ; ++i)
{
pthread_join(ids[i], NULL);
}

//删除信号量
semctl(sid, 1, IPC_RMID);

return 1;
}