#include <iostream> // std::cout

#include <thread>                // std::thread

#include <mutex>                // std::mutex, std::unique_lock

#include <condition_variable>    // std::condition_variable

std::mutex mtx;            // 全局互斥锁.

std::condition_variable cv; // 全局条件变量.

bool ready = false;        // 全局标志位.

void do_print_id(int id)

{

std::unique_lock <std::mutex> lck(mtx);

std::cout << "begin thread " << id << '\n';

while (!ready)

{

/*

如果标志位不为 true, 则等待...

当前线程被阻塞, 当全局标志位变为 true 之后, 线程被唤醒, 继续往下执行打印线程编号id.

*/

std::cout << "wait: " << id << std::endl;

cv.wait(lck);

}

std::cout << "thread " << id << '\n';

}

void go()

{

std::unique_lock <std::mutex> lck(mtx);

std::this_thread::sleep_for(std::chrono::milliseconds(2000));

ready = true; // 设置全局标志位为 true.

//cv.notify_all(); // 唤醒所有线程.

cv.notify_one();//

}

int main()

{

std::thread threads[10];

// spawn 10 threads:

for (int i = 0; i < 10; ++i)

threads[i] = std::thread(do_print_id, i);

std::cout << "10 threads ready to race...\n";

getchar();

go(); // go!

for (auto& th : threads)

th.join();

getchar();

return 0;

}