线程3——信号量
创建信号量，并赋予初值
int sem_init(sem_t *sem, int pshared, unsigned int value);
销毁信号量
int sem_destroy(sem_t *sem);
阻塞，信号量数值-1
int sem_wait(sem_t *sem);
非阻塞申请
int sem_trywait(sem_t *sem);
计时申请一个信号量
int sem_timedwait(sem_t *sem, const struct timespec *abs_timeout);
发送信号量，数值 +1
int sem_post(sem_t *sem);
获取信号量值
int sem_getvalue(sem_t *sem, int *sval);
示例：和互斥锁案例相同
1 #include <stdio.h> 2 #include <unistd.h> 3 #include <stdlib.h> 4 #include <semaphore.h> 5 6 7 void* task1(void *arg); 8 void* task2(void *arg); 9 void* task3(void *arg); 10 11 static int i = 10 ; 12 static sem_t sem; //信号量指针 13 14 15 int main(void) 16 { 17 int ret; 18 sem_init(&sem,0,1); //初始化信号量 初值为1 19 20 //声明三个指针，指向线程的id 21 pthread_t tid1,tid2,tid3; 22 //创建三个新线程，用刚才的指针， 23 pthread_create(&tid1,NULL,task1,(void*)5); 24 pthread_create(&tid2,NULL,task2,(void*)6); 25 pthread_create(&tid3,NULL,task3,(void*)7); 26 27 printf("Main thread\r\n"); 28 //等待线程结束运行 29 pthread_join(tid1,(void **)&ret); 30 pthread_join(tid2,(void **)&ret); 31 pthread_join(tid3,(void **)&ret); 32 33 sleep(1); 34 printf("New thread1 id:%ld\r\n",tid1); 35 printf("New thread2 id:%ld\r\n",tid2); 36 printf("New thread3 id:%ld\r\n",tid3); 37 //销毁信号量 38 sem_destroy(&sem); 39 40 41 } 42 43 void* task1(void *arg) 44 { 45 while(i<30){ 46 //信号量-1 47 sem_wait(&sem); 48 i++; 49 printf("%d\r\n",i); 50 //信号量+1 51 sem_post(&sem); 52 usleep(1); 53 } 54 pthread_exit(NULL); 55 56 } 57 58 void* task2(void *arg) 59 { 60 while(i<30){ 61 //信号量-1 62 sem_wait(&sem); 63 i++; 64 printf("%d\r\n",i); 65 //信号量+1 66 sem_post(&sem); 67 usleep(1); 68 } 69 pthread_exit(NULL); 70 71 } 72 73 void* task3(void *arg) 74 { 75 while(i<30){ 76 //信号量-1 77 sem_wait(&sem); 78 i++; 79 printf("%d\r\n",i); 80 //信号量+1 81 sem_post(&sem); 82 usleep(1); 83 } 84 pthread_exit(NULL); 85 86 }
计时申请信号量：（结构体见上一篇条件变量）
1 struct timeval now; 2 struct timespec outtime; 3 gettimeofday(&now, NULL);//获取当前时间 4 outtime.tv_sec = now.tv_sec + 5; //设定唤醒的绝对时间是当前时间+5s 5 outtime.tv_nsec = now.tv_usec * 1000; 6 sem_timedwait(&sem, &outtime);
