c++ - 几个线程 : catching the moment when they all finish work

Question

我有几个线程，我需要捕获它们全部完成工作的时刻。怎么做？

for (int i = 1; i < 3; i++) {
   std::thread threads1(countFile, i);
   i++;
   std::thread threads2(countFile, i);
   threads1.detach();
   threads2.detach();
}

// wait until all the threads run out---

// to do next function ob object which uses by threads--

Answer 1

考虑在 for block 之外创建 std::thread 对象并调用 join() 而不是 detach() :

// empty (no threads associated to them yet)
std::array<std::thread, 2> threads1, threads2;

for (int i = 0; i < 2; i++) {
   threads1[i] = std::thread(countFile, i+1); // create thread
   i++;
   threads2[i] = std::thread(countFile, i+1); // create thread
}

// ...

// join on all of them
for (int i = 0; i < 2; i++) {
   threads1[i].join();
   threads2[i].join();
}

// at this point all those threads have finished

不调用 detach() 意味着必须在 std 的析构函数之前调用 join()::thread 对象被调用(无论线程是否已经完成)。

出于这个原因，我将 std::thread 对象放在了 for block 之外。否则，必须在 for block 内调用 join()。