thread.cpp

#include <condition_variable> // std::condition_variable
#include <iostream>           // std::cout
#include <mutex>              // std::mutex, std::unique_lock
#include <thread>             // std::thread

// https://www.cnblogs.com/haippy/p/3252041.html

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 << "thread try exec" << id << '\n';
  while (!ready)  // 如果标志位不为 true, 则等待...
    cv.wait(lck); // 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 << "thread done " << id << '\n';
}

void go() {
  std::unique_lock<std::mutex> lck(mtx);
  ready = true;    // 设置全局标志位为 true.
  cv.notify_all(); // 唤醒所有线程.
}

int main() {
  std::thread threads[10];
  // spawn 10 threads:

  // std::thread之后thread就启动了
  for (int i = 0; i < 10; ++i)
    threads[i] = std::thread(do_print_id, i);

  std::cout << "10 threads ready to race...\n";
  go(); // go!

  for (auto &th : threads)
    th.join();

  return 0;
}