信号量

信号量(信号灯)

mutex初始化为1
lock之后为0
unlock之后为1
mutex实现的同步都是串行的

sem相当于有多个mutex, 并行

(1) 头文件: semaphore.h

(2) 信号量类型: sem_t; 加强版互斥锁

(3) 主要函数

初始化信号量:int sem_init(sem_t *sem, int pshared, unsigned int value);
  0 线程同步
  1 进程同步
  value: 最多有几个线程操作共享数据

销毁信号int sem_destroy(sem_t *sem);

加锁
int sem_wait(sem_t *sem);
调用一次相当于对sem做了-1操作
如果sem值为0, 线程会阻塞

int sem_trywait(sem_t *sem); 尝试加锁, 不阻塞, 直接返回

int sem_timedwait(sem_t *sem, const struct timespec *abs_timeout); 限时加锁

解锁int sem_post(sem_t *sem);

(4) 使用信号量实现生产者, 消费者模型

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <pthread.h>
#include <semaphore.h>

sem_t produce_sem;
sem_t custom_sem;

typedef struct node {
    int data;
    struct node *next;
}Node;

Node *head = NULL;

void* producer(void *arg) {
    while (1) {
        sem_wait(&produce_sem);
        Node *node = (Node *)malloc(sizeof(Node));
        node->data = rand() % 1000;
        node->next = head;
        head = node;
        printf("++++生产者: %lu, %d\n", pthread_self(), node->data);
        sem_post(&custom_sem);
        sleep(rand()%5);
    }
    return NULL;
}

void* customer(void *arg) {
    while (1) {
        sem_wait(&custom_sem);
        Node *del = head;
        head = head->next;
        printf("----消费者: %lu, %d\n", pthread_self(), del->data);
        free(del);
        sem_post(&produce_sem);
        sleep(rand()%5);
    }
    return NULL;
}

int main(int argc, const char *argv[]) {
    pthread_t thid[2];
    // 初始化信号量
    sem_init(&produce_sem, 0, 4);
    sem_init(&custom_sem, 0, 0);
    
    pthread_create(&thid[0], NULL, producer, NULL);
    pthread_create(&thid[1], NULL, customer, NULL);

    for (int i = 0; i < 2; i++) {
        pthread_join(thid[i], NULL);
    }
    
    sem_destroy(&produce_sem);
    sem_destroy(&custom_sem);

    return 0;
}

posted @ 2019-04-19 21:40  张飘扬  阅读(372)  评论(0编辑  收藏  举报