学步园

一、多线程的创建和启动

               一个多线程的程序是通过先创建后启用的方式运行起来的。可以在创建的时候传递参数，也可以在结束的时候返回参数。注意当第二个进程sleep时，第一个线程也在运行。当线程退出时，才继续向下运行主程序。上一个线程未退出，是不会向下执行主程序的。

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

pthread_t tid,tid2;
void* myfunc1(void* argv){
    printf("receive %s\n",(char*)argv);
    printf("New process:  PID: %d,TID: %u.\n",getpid(),pthread_self());      //得到TID
    printf("New process:  PID: %d,TID: %u.\n",getpid(),tid);
    //sleep(6);   //测试结果为6秒以后阻塞的信息一起输出
    sleep(2);
    pthread_exit((void*)1);
}

void* myfunc2(void* argv){
    printf("the second thread is running......\n");
    sleep(3);
    return (void*)2;
}

int main(){
    void* ret;
    if(pthread_create(&tid,NULL,myfunc1,"gaga")!=0){     //传递参数
        printf("create error\n");
        exit(1);
    }
    if(pthread_create(&tid2,NULL,myfunc2,NULL)!=0){
        printf("create error\n");
        exit(1);
    }
    printf("the pthread id is %d \n",tid);
    printf("Main process: PID: %d,TID: %u.\n",getpid(),pthread_self());
    if(pthread_join(tid,&ret) !=0){
        printf("join thread 1 error!\n");
        return 1;
    }
    printf("wa kakaka it is %d\n",(int)ret);
    if(pthread_join(tid2,&ret) != 0){
        printf("join thread 2 error!\n");
        return 1;
    }
    printf(" %d \n",(int)ret);
}

运行结果为：

[fsy@localhost thread]$ ./thread_create 
the pthread id is -1216914576                 //此处还未初始化
Main process: PID: 6333,TID: 3078055616.
the second thread is running......            //2线程先运行然后sleep
receive gaga                                  //1线程运行
New process:  PID: 6333,TID: 3078052720.
New process:  PID: 6333,TID: 3078052720.
wa kakaka it is 1                            //两秒后打印,sleep(6)就在此阻塞6秒
 2                                           //2线程退出，再运行主程序
[fsy@localhost thread]$ 

二、取消线程

             通过pthread_cancel() 函数来结束另一个线程。

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

pthread_t tid,tid2;
void* myfunc1(void* argv){
    pthread_setcancelstate(PTHREAD_CANCEL_ENABLE,NULL); //设置可被其他进程取消
    while(1){
        printf("thread 1 is read to be killed\n");
        sleep(1);
    }
    return 0;
}

void* myfunc2(void* argv){
    printf("thread 2 is running!\n");
    sleep(3);
    if(pthread_cancel(tid) == 0){
        printf("Thread 2  will kill Thread 1\n");
    }
    return 0;
}

int main(){
    if(pthread_create(&tid,NULL,myfunc1,NULL)!=0){
        printf("create error\n");
        exit(1);
    }
    if(pthread_create(&tid2,NULL,myfunc2,NULL)!=0){
        printf("create error\n");
        exit(1);
    }
    if(pthread_join(tid,NULL) !=0){
        printf("join thread 1 error!\n");
        return 1;
    }
    printf("Thread 1 is never back.....\n");
    if(pthread_join(tid2,NULL) != 0){
        printf("join thread 2 error!\n");
        return 1;
    }
}

     运行输出结果为：

[fsy@localhost thread]$ ./thread
thread 2 is running!
thread 1 is read to be killed
thread 1 is read to be killed
thread 1 is read to be killed
Thread 2  will kill Thread 1
Thread 1 is never back.....

三、互斥锁

               两个进程同时访问一个数据就需要加锁。

      用pthread_mutex_lock、pthread_mutex_unlock控制锁。pthread_mutex_destory删除锁。pthread_mutex_trylock判断是否加锁。

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

pthread_mutex_t mutex;
pthread_t tid,tid2;
int meter=0;
int seconds=0;
void* myfunc1(void* argv){
    pthread_mutex_lock(&mutex);    //上锁
    while(1){
        printf("thread is running %d seconds it is %d meter\n",seconds,meter);
        meter++;
        seconds++;
        sleep(1);
    }
    pthread_mutex_unlock(&mutex);  //去锁
    return 0;
}

void* myfunc2(void* argv){
    sleep(1);
    pthread_mutex_lock(&mutex);
    while(1){
        meter++;
        seconds++;
    }
    pthread_mutex_unlock(&mutex);
}

int main(){
    pthread_mutex_init(&mutex,NULL);    //第二个参数NULL为互斥锁
    if(pthread_create(&tid,NULL,myfunc1,NULL)!=0){
        printf("create error\n");
        exit(1);
    }
    if(pthread_create(&tid2,NULL,myfunc2,NULL)!=0){
        printf("create error\n");
        exit(1);
    }
    if(pthread_join(tid,NULL) !=0){
        printf("join thread 1 error!\n");
        return 1;
    }
    if(pthread_join(tid2,NULL) != 0){
        printf("join thread 2 error!\n");
        return 1;
    }
}

     经过加锁，能够依次输出数字。

四、信号量

             解决同步问题，加锁可以用信号量，它更强大一些，可以用它来控制进程的运行顺序。

             sem_init()初始化一个函数。sem_wait()执行P操作。sem_post()执行V操作。sem_destory()销毁信号量。

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

pthread_t tid,tid2;
sem_t sem1;
sem_t sem2;
void* myfunc1(void* argv){
    sem_wait(&sem1);    //p操作使其他线程无法访问
    sleep(2);
    printf("thread 1 is running....\n");
    sem_post(&sem2);   //V操作使2线程可以运行
}

void* myfunc2(void* argv){
    sem_wait(&sem2);   //在未进行V操作之前会卡住 
    printf("thread 2 is running!\n");
    sleep(1);
    sem_post(&sem1);
}

int main(){
    if(pthread_create(&tid,NULL,myfunc1,NULL)!=0){
        printf("create error\n");
        exit(1);
    }
    if(pthread_create(&tid2,NULL,myfunc2,NULL)!=0){
        printf("create error\n");
        exit(1);
    }
    //第二个参数为固定的0，第三个参数为1表示线程可访问，0表示线程不可访问
    sem_init(&sem1,0,1);
    sem_init(&sem2,0,0);
    if(pthread_join(tid,NULL) !=0){
        printf("join thread 1 error!\n");
        return 1;
    }
    if(pthread_join(tid2,NULL) != 0){
        printf("join thread 2 error!\n");
        return 1;
    }
    sem_destroy(&sem1);
    sem_destroy(&sem2);
    printf("finish!\n");
}

    通过信号量和P、V的操作实现了线程同步的控制。
 

 本篇博客出自 
阿修罗道，转载请注明出处：http://blog.csdn.net/fansongy/article/details/6882586