线程同步

有时候我们需要用到线程同步来控制线程运行顺序。

/***
synchro.c
***/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<pthread.h>
#include<errno.h>

void *func(void *arg)
{
    int threadno = *(int *)arg;
    int i = 0;
    for(; i < 10; i++)
    {
        printf("%d thread%d\n",threadno,i);
        sleep(1);
    }
    return NULL;
}

int main()
{
    pthread_t t1,t2;
    int i = 1,j = 2;
    pthread_create(&t1,NULL,func,&i);
    pthread_create(&t2,NULL,func,&j);
    
    pthread_join(t1,NULL);    
    pthread_join(t2,NULL);

    printf("main exit\n");
    return EXIT_SUCCESS;
}

exbot@ubuntu:~/wangqinghe/thread/20190729$ ./synchro

2 thread0

1 thread0

2 thread1

1 thread1

2 thread2

1 thread2

2 thread3

1 thread3

2 thread4

1 thread4

2 thread5

1 thread5

2 thread6

1 thread6

2 thread7

1 thread7

2 thread8

1 thread8

2 thread9

1 thread9

main exit

线程1和线程2互相抢占资源。

用互斥的方式来控制只有一个线程来使用资源。

/***
lock.c
***/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<pthread.h>
#include<errno.h>

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

void *func(void *arg)
{

    pthread_mutex_lock(&mutex);    

    int threadno = *(int *)arg;
    int i = 0;
    for(; i < 10; i++)
    {
        printf("%d thread%d\n",threadno,i);
        sleep(1);
    }
    pthread_mutex_unlock(&mutex);
    return NULL;
}

int main()
{
    pthread_t t1,t2;
    int i = 1,j = 2;
    pthread_create(&t1,NULL,func,&i);
    pthread_create(&t2,NULL,func,&j);
    
    pthread_join(t1,NULL);    
    pthread_join(t2,NULL);

    printf("main exit\n");
    return EXIT_SUCCESS;
}

运行结果：

exbot@ubuntu:~/wangqinghe/thread/20190729$ ./synchro1

2 thread0

2 thread1

2 thread2

2 thread3

2 thread4

2 thread5

2 thread6

2 thread7

2 thread8

2 thread9

1 thread0

1 thread1

1 thread2

1 thread3

1 thread4

1 thread5

1 thread6

1 thread7

1 thread8

1 thread9

main exit

 

线程2先进入后一直运行到任务结束，对mutex解锁后线程1才进入。

PTHREAD_MUTEX_INITIALIZER 是初始化一个快速锁的宏定义。

Pthread_mutex_t = PTHREAD_MUTEX_INITIALIZER

 

加锁解锁函数：

int pthread_mutex_lock(&mutex);

int pthread_mutex_unlock(&mutex);