线程锁进行互斥访问（程序示例）

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>

pthread_mutex_t Device_mutex = PTHREAD_MUTEX_INITIALIZER;

int count=0;
void * thread_func1()
{
    printf("thread id is %d
",pthread_self());
    while(1)
    {
//        printf("thread  1 ,sleep 20 ,quite c>=10,
");
        pthread_mutex_lock(&Device_mutex);
        printf("thread  1 ,sleep 20 ,quite c>=10,  c=%d 
",count);
        count++;
        if(count>=10)
        {
            pthread_mutex_unlock(&Device_mutex);
            break;
        }
        else
        {
            pthread_mutex_unlock(&Device_mutex);
        }
        sleep(20);
    }

    printf("     thread  1  quite
");
    return NULL;
}
void * thread_func2()
{
    printf("thread id is %d 
 ",pthread_self());
    while(1)
    {
//        printf("thread  2 ,sleep 5 ,quite c>=30,
");
        pthread_mutex_lock(&Device_mutex);
        printf("thread  2 ,sleep 5 ,quite c>=30, c= %d 
",count);
        count++;
        if(count>=30)
        {
            pthread_mutex_unlock(&Device_mutex);
            break;
        }
        else
        {
            pthread_mutex_unlock(&Device_mutex);
        }
        sleep(5);
    }
    printf("     thread  2  quite
");
    return NULL;
}
int main()
{
    pthread_t thread1, thread2;
//    pthread_mutex_init(&Device_mutex,NULL);
    if(pthread_create(&thread1,NULL,thread_func1,NULL) == -1)
    {
        printf("create IP81 Thread error !n");
        exit(1);
    }
    sleep(1);
    if(pthread_create(&thread2,NULL,thread_func2,NULL) == -1)
    {
        printf("create IP81_2 Thread error!n");
        exit(1);
    }
    sleep(1);
    pthread_join(thread1,NULL);
    pthread_join(thread2,NULL);
    pthread_mutex_destroy(&Device_mutex);
    return 0;
}

线程的最大特点是资源的共享性，但资源共享中的同步问题是多线程编程的难点。linux下提供了多种方式来处理线程同步，最常用的是互斥、读写锁、条件变量和信号量。

1、互斥锁（mutex）

    通过锁机制实现线程间的同步。同一时刻只允许一个线程执行一个关键部分的代码。

int pthread_mutex_init(pthread_mutex_t *mutex,const pthread_mutex_attr_t *mutexattr);

int pthread_mutex_lock(pthread_mutex *mutex);

int pthread_mutex_destroy(pthread_mutex *mutex);

int pthread_mutex_unlock(pthread_mutex *

(1)先初始化锁init()或静态赋值pthread_mutex_t mutex=PTHREAD_MUTEX_INITIALIER

attr_t有:

PTHREAD_MUTEX_TIMED_NP:其余线程等待队列

PTHREAD_MUTEX_RECURSIVE_NP:嵌套锁,允许线程多次加锁,不同线程,解锁后重新竞争

PTHREAD_MUTEX_ERRORCHECK_NP:检错,与一同,线程请求已用锁,返回EDEADLK;

PTHREAD_MUTEX_ADAPTIVE_NP:适应锁,解锁后重新竞争

(2)加锁,lock,trylock,lock阻塞等待锁,trylock立即返回EBUSY

(3)解锁,unlock需满足是加锁状态,且由加锁线程解锁

(4)清除锁,destroy(此时锁必需unlock,否则返回EBUSY,//Linux下互斥锁不占用内存资源