这是什么的std ::的Thread.join（）呢？(What does std::thread.

通过从C ++参考定义：

阻止当前线程，直到被标识的线程*this完成它的执行。

那么，这是否使用时的意思.join()有没有必要mutex.lock()当线程调用一些功能？我是新来的相互排斥和线程，所以我有点困惑。

注：我发现了一本书C ++并发在行动，我读的书。它写的很好的多线程上像我这样的初学者。

谢谢大家的帮助。

Answer 1:

你仍然需要互斥和条件。加入一个线程进行执行一个线程等待另一个线程完成运行。你仍然需要互斥来保护共享资源。它允许的main（）在这个例子中，以等待所有线程戒烟本身之前完成。

#include <iostream>
#include <thread>
#include <chrono>
#include <mutex>

using namespace std;



int global_counter = 0;
std::mutex counter_mutex;

void five_thread_fn(){
    for(int i = 0; i<5; i++){
        counter_mutex.lock();
        global_counter++;
        counter_mutex.unlock();
        std::cout << "Updated from five_thread"  << endl;
        std::this_thread::sleep_for(std::chrono::seconds(5));
    }
    //When this thread finishes we wait for it to join
}

void ten_thread_fn(){
    for(int i = 0; i<10; i++){
        counter_mutex.lock();
        global_counter++;
        counter_mutex.unlock();
        std::cout << "Updated from ten_thread"  << endl;
        std::this_thread::sleep_for(std::chrono::seconds(1));
    }
    //When this thread finishes we wait for it to join
}
int main(int argc, char *argv[]) {
    std::cout << "starting thread ten..." << std::endl;
    std::thread ten_thread(ten_thread_fn);

    std::cout << "Running ten thread" << endl;
    std::thread five_thread(five_thread_fn);


    ten_thread.join();
    std::cout << "Ten Thread is done." << std::endl;
    five_thread.join();
    std::cout << "Five Thread is done." << std::endl;
}

请注意，输出可能是这样的：

starting thread ten...
Running ten thread
Updated frUopmd atteend_ tfhrroema df
ive_thread
Updated from ten_thread
Updated from ten_thread
Updated from ten_thread
Updated from ten_thread
Updated from five_thread
Updated from ten_thread
Updated from ten_thread
Updated from ten_thread
Updated from ten_thread
Updated from ten_thread
Updated from five_thread
Ten Thread is done.
Updated from five_thread
Updated from five_thread
Five Thread is done.

由于的std :: cout是共享资源的访问和使用还应当互斥保护了。