[百晓生]-linux之多线程同步技术

 

[百晓生]-linux之多线程同步技术

 

１.同步机制
    线程同步机制主要有：互斥量／信号量／条件变量／读写锁等。
 
２.技术示例
    创建２个计数线程Ａ和Ｂ，每次计数加１，当为偶数时，Ａ线程计数；当为奇数时，Ｂ线程计数。
    源码：

//thread_mutex_cond.c

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <pthread.h>

#define MAX_COUNT 9

pthread_mutex_t mutex;

pthread_cond_t cond;

int count=0;

void AddCount_Odd_Func(void);

void AddCount_Even_Func(void);

int main()

{

     int ret;

pthread_t odd_thread,even_thread;

pthread_attr_t thread_attr;

count = 0;

pthread_mutex_init(&mutex,NULL);

pthread_cond_init(&cond,NULL);

ret = pthread_attr_init(&thread_attr);

if (ret != 0)

{

perror("Attribute Creation Failed");

exit(EXIT_FAILURE);

} 

pthread_attr_setdetachstate(&thread_attr,PTHREAD_CREATE_DETACHED); 

ret=pthread_create(&odd_thread,&thread_attr,(void *)&AddCount_Odd_Func,NULL);

if(ret != 0)

{

perror("Thread Creation Failed");

          exit(EXIT_FAILURE);

}

   ret = pthread_create(&even_thread,&thread_attr,(void *)&AddCount_Even_Func, NULL);

if (ret != 0)

{

perror("Thread Creation Failed");

              exit(EXIT_FAILURE);

}

while(count<MAX_COUNT);    

    printf("Finished!\n");

    pthread_cond_destroy(&cond);

    pthread_mutex_destroy(&mutex);

    return 0;

}

void AddCount_Odd_Func(void)

{

pthread_mutex_lock(&mutex);

while(count<MAX_COUNT)

{

if(count%2==1)

{

count++;

printf("AddCount_Odd_Func():count=%d.\n",count);

pthread_cond_signal(&cond);

}

else

pthread_cond_wait(&cond, &mutex);

}

pthread_mutex_unlock(&mutex);

}

void AddCount_Even_Func(void)

{

pthread_mutex_lock(&mutex);

while(count<MAX_COUNT)

{

if(count%2==0)

{

count++;

printf("AddCount_Even_Func():count=%d.\n",count);

pthread_cond_signal(&cond);

}

else

pthread_cond_wait(&cond, &mutex);

}

pthread_mutex_unlock(&mutex);

}  

３.mystery注解
１）示例中，创建了互斥量mutex与条件量cond。mutex用于互斥操作，cond用于在相关条件成立时进行操作
２）pthread_attr_setdetachstate()函数设置线程为分离状态
３）pthread_cond_wait()使线程阻塞
４）pthread_cond_broadcast()函数用来唤醒所有被阻塞在条件变量cond上的线程。
        要注意，被唤醒后的这些线程将再次竞争相应的互斥量
５）pthread_cond_init()函数创建条件变量
６）pthread_cond_signal()函数用来释放被阻塞在条件变量cond上的线程