linux 多线程的学习

最新推荐文章于 2023-07-15 15:21:48 发布

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最新推荐文章于 2023-07-15 15:21:48 发布

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分类专栏： linux

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本文详细介绍了pthread库中的几个关键函数：pthread_exit用于从线程退出并返回一个值；pthread_join用于等待一个线程结束并获取其返回值；pthread_cancel用于取消一个正在运行的线程；而pthread_detach则用于分离线程，使主线程不必等待该线程结束。

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pthread_exit的一个目标是，把一个指针传递给pthread_join函数

pthread_join函数的思路是：通过参数的返回值，将该指针值返回给pthread_join的调用者

#include<pthread.h>
#include<iostream>
#include<unistd.h>

using namespace std;
void* thread(void* arg){
 cout<<(long)arg<<endl;
  return (void*)20;
}
int main(){
  pthread_t tid;
  int err=pthread_create(&tid,NULL,thread,(void*)2);
  if(err!=0){
    cout<<"create failure"<<endl;
    return -1;
  }
  long* r;
  pthread_join(tid,(void**)&r);
  cout<<(long)r<<endl;
  return 0;
}

编译：g++ tt.cc -lpthread

#include<pthread.h>
#include<iostream>
#include<unistd.h>

using namespace std;

void *thread(void *arg)
{
    cout << "in thread, tid = " << pthread_self() << endl;

    long i = 2;
    pthread_exit(&i);

    return (void *)12;
}

int main()
{
    pthread_t tid;
    if(pthread_create(&tid, NULL, thread, 0) != 0)
    {
        cout << "pthread_create error" << endl;
        return 0;
    }

    long *r;
    pthread_join(tid, (void**)&r);

    cout << r << endl;

    cout << *r << endl;

    cout << "in main thread, tid = " << pthread_self() << endl;
    return 0;
}

上述代码中，*r指向了一个不再存在的对象，输出结果为：

in thread, tid = 139814095632128
0x7f2901812e88
139814095632128
in main thread, tid = 139814112380736

将

long i = 2;
    pthread_exit(&i);

改为pthread_exit(new long(2));

in thread, tid = 140514155718400
0x7fcbf80008c0
2
in main thread, tid = 140514172467008

三：pthread_cancel的使用：

#include<pthread.h>
#include<iostream>
#include<unistd.h>

using namespace std;

void *thread(void *arg)
{
    cout << "in thread, tid = " << pthread_self() << endl;

    sleep(2);

    return (void *)12;
}

int main()
{
    pthread_t tid;
    if(pthread_create(&tid, NULL, thread, 0) != 0)
    {
        cout << "pthread_create error" << endl;
        return 0;
    }
    pthread_cancel(tid);

    long *r;
    pthread_join(tid, (void**)&r);

    cout << PTHREAD_CANCELED << endl;
    cout << r << endl;

    cout << "in main thread, tid = " << pthread_self() << endl;
    return 0;
}

执行结果：
in thread, tid = 140456113821440

四：pthread_detach的使用：

若pthread_join比pthread_detach先调用，也能获取到退出信息

#include<pthread.h>
#include<iostream>
#include<unistd.h>
#include<errno.h>

using namespace std;

void *thread(void *arg)
{
    cout << "in thread, tid = " << pthread_self() << endl;

    sleep(2);

    pthread_detach(pthread_self());

    cout << "nihao" << endl;

    return (void *)0;
}

int main()
{
    pthread_t tid;
    if(pthread_create(&tid, NULL, thread, 0) != 0)
    {
        cout << "pthread_create error" << endl;
        return 0;
    }

    int *r;
    int s = pthread_join(tid, (void **)&r);
    if(s == EINVAL)
    {
        cout << "join error" << endl;
    }
    else
    {
        cout << r << endl;
    }

    cout << "in main thread, tid = " << pthread_self() << endl;

    return 0;
}

运行结果：

in thread, tid = 140355871602432
nihao
0
in main thread, tid = 140355888351040