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  • 条件锁详解

    等待线程

      1。使用pthread_cond_wait前要先加锁

      2。pthread_cond_wait内部会解锁,然后等待条件变量被其它线程激活

      3。pthread_cond_wait被激活后会再自动加锁

    激活线程:

      1。加锁(和等待线程用同一个锁)

      2。pthread_cond_signal发送信号

      3。解锁

       激活线程的上面三个操作在运行时间上都在等待线程的pthread_cond_wait函数内部。

       程序示例:

       #include <stdio.h>

       #include <pthread.h>

       #include <unistd.h>

       pthread_mutex_t count_lock;

         pthread_cond_t count_nonzero;

       unsigned count = 0;

       void * decrement_count(void *arg)

      {

      pthread_mutex_lock (&count_lock);

      printf("decrement_count get count_lock ");

      while(count==0) {

      printf("decrement_count count == 0 ");

      printf("decrement_count before cond_wait ");

      pthread_cond_wait( &count_nonzero, &count_lock);

      printf("decrement_count after cond_wait ");

      }

      count = count -1;

      pthread_mutex_unlock (&count_lock);

      }

      void * increment_count(void *arg){

      pthread_mutex_lock(&count_lock);

      printf("increment_count get count_lock ");

      if(count==0) {

      printf("increment_count before cond_signal ");

      pthread_cond_signal(&count_nonzero);

      printf("increment_count after cond_signal ");

      }

      count=count+1;

      pthread_mutex_unlock(&count_lock);

      }

      int main(void)

      {

      pthread_t tid1,tid2;

      pthread_mutex_init(&count_lock,NULL);

      pthread_cond_init(&count_nonzero,NULL);

      pthread_create(&tid1,NULL,decrement_count,NULL);

      sleep(2);

      pthread_create(&tid2,NULL,increment_count,NULL);

      sleep(10);

      pthread_exit(0);

      }

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  • 原文地址:https://www.cnblogs.com/lgz24/p/3603269.html
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