[C++知识库]C++并发编程(3)：移交线程归属权

C++并发编程(3)和C++并发编程(2)对应书中第二章，C++并发编程(3)是第二章的收尾部分

移交线程归属权

对于一个具体的执行线程，其归属权可在多个thread实例间转移，有以下几种用法

1. 在thread实例间转移线程所属权
2. thread对象做返回值
3. thread对象作为函数参数
4. 向STL容器中装载thread对象

示例代码如下：

#include <iostream>
#include <thread>
#include <string.h>
#include <vector>

using namespace std;

const int thread_num = 10;

void smile()
{
    cout << "Smile" << endl;
}

void cry()
{
    cout << "cry" << endl;
}

thread test()
{
    thread t_(smile);

    cout << "test t_ id:" << t_.get_id() << endl;

    return t_;
}

void test02(thread t_)
{
    if (t_.joinable())
    {
        cout << "test02 t_ joinable" << endl;
        cout << "test02 t_ id:" << t_.get_id() << endl;
        t_.join();
    }
    else
    {
        cout << "test02 t_ unjoinable" << endl;
        cout << "test02 t_ id:" << t_.get_id() << endl;
    }
}

int main()
{
    thread t;
		//从函数内部接受thread对象
    t = test();
    cout << "main t id:" << t.get_id() << endl;
    if(t.joinable())
    {
				cout << "main t joinable" << endl;
        t.join();
    }

    thread t1 = thread(cry);
    cout << "main t1 id:" << t1.get_id() << endl;
		//t = move(t1);	错误!!!	

		//在thread对象间传递线程所属权
    thread t2 = move(t1);
    cout << "main t2 id:" << t2.get_id() << endl;

		//向函数内部传递thread对象
    test02(move(t));
    t2.join();

		//用容器装在thread对象
    vector<thread> v;
    for (int i = 0; i < thread_num; ++i)
    {
        if (i % 2 == 0)
        {
            v.emplace_back(smile);
        }
        else
        {
            v.emplace_back(cry);
        }
    }
    int k = 0;
    for(auto& v_t:v)
    {
        cout << "v_t " << k << " id:" << v_t.get_id() << endl;
        v_t.join();
        k++;
    }

    cout << "main end" << endl;

    return 0;
}

运行输出：

prejudice@prejudice-VirtualBox:~/Cplus_learning/build$ ../bin/thread_03
test t_ id:140260519634688
main t id:140260519634688
main t joinable
Smile
main t1 id:140260519634688
main t2 id:140260519634688
test02 t_ unjoinable
test02 t_ id:thread::id of a non-executing thread
cry
v_t 0 id:140260519634688
Smile
cry
Smile
Smile
cry
cry
cry
Smile
cry
Smile
v_t 1 id:140260511241984
v_t 2 id:140260502849280
v_t 3 id:140260494456576
v_t 4 id:140260411438848
v_t 5 id:140260403046144
v_t 6 id:140260394653440
v_t 7 id:140260386260736
v_t 8 id:140260377868032
v_t 9 id:140260369475328
main end

若向已关联线程的thread对象转移线程所属权，则std::terminate()函数会被调用，终止整个程序

因此只要std::thread对象正管控一个线程，就不能简单向其赋新值

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