互斥锁(mutex) 通过锁机制实现线程间的同步。
1、初始化锁。在Linux下,线程的互斥量数据类型是pthread_mutex_t。在使用前,要对它进行初始化。
2、静态分配:pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER
3、动态分配:int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutex_attr_t *mutexattr)
4、加锁。对共享资源的访问,要对互斥量进行加锁,如果互斥量已经上了锁,调用线程会阻塞,直到互斥量被解锁。
int pthread_mutex_lock(pthread_mutex *mutex)int pthread_mutex_trylock(pthread_mutex_t *mutex)
解锁。在完成了对共享资源的访问后,要对互斥量进行解锁。
int pthread_mutex_unlock(pthread_mutex_t *mutex)
销毁锁。锁在是使用完成后,需要进行销毁以释放资源。
int pthread_mutex_destroy(pthread_mutex *mutex)
#include <cstdio>
#include <cstdlib>
#include <unistd.h>
#include <pthread.h>
#include "iostream"
using namespace std
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER
int tmp
void* thread(void *arg)
{
cout << "thread id is " << pthread_self() << endl
pthread_mutex_lock(&mutex)
tmp = 12
cout << "Now a is " << tmp << endl
pthread_mutex_unlock(&mutex)
return NULL
}
int main()
{
pthread_t id
cout << "main thread id is " << pthread_self() << endl
tmp = 3
cout << "In main func tmp = " << tmp << endl
if (!pthread_create(&id, NULL, thread, NULL))
{
cout << "Create thread success!" << endl
}
else
{
cout << "Create thread failed!" << endl
}
pthread_join(id, NULL)
pthread_mutex_destroy(&mutex)
return 0
}
//编译:g++ -o thread testthread.cpp -lpthread
目测是线程退出时没有解开互斥锁,导致其它线程一直在等互斥锁被解开。
以下是修改后的thrd_func函数代码:
//线程函数入口void *thrd_func(void *arg)
{
int thrd_num = (int)arg
int delay_time = 0
int count = 0
int res
res = pthread_mutex_lock(&mutex)//互斥锁上锁
if(res)
{
printf("Thread %d lock failed\n",thrd_num)
pthread_exit(NULL)
}
printf("Thread %d is starting\n",thrd_num)
for(count = 0count < REPEAT_NUMBERcount++)
{
delay_time = (int)(rand()%5)//随机时间数
sleep(delay_time)
printf("\tThread %d: job %d delay =%d\n",thrd_num,count,delay_time)
}
pthread_mutex_unlock(&mutex) // 解开互斥锁
printf("Thread %d finished\n",thrd_num)
pthread_exit(NULL)
}
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