multithreading - Managing Worker Thread Wake-Up in C++: Separate vs. Shared Condition Variables? - Stack Overflow

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I have a queue of worker thread IDs in C++, and a coordinator thread wakes each thread in order. The woken thread then interacts with the coordinator thread to perform some work. Once done, the coordinator wakes the next thread.

I am considering two approaches to implement this:

1. Separate Condition Variables: Each worker thread has its own std::condition_variable, stored in a queue along with its thread ID. The coordinator signals the respective condition variable to wake up a specific thread.
2. Single Condition Variable: All worker threads wait on a shared std::condition_variable, using a predicate to check if their ID matches the one chosen by the coordinator.

Approach 2: Using a Single Condition Variable

Coordinator Thread:

while (true) {
  {
    std::lock_guard<std::mutex> lock(mtx);
    id_chosen_by_coordinator = workerThreads.front();
    workerThreads.pop();
  }
  cv.notify_all();  // Wake up all worker threads, but only one will proceed
  ...
}

Worker Thread:

std::unique_lock<std::mutex> lock(mtx);
cv.wait(lock, []() { return myid == id_chosen_by_coordinator; });
...

Which of these approaches is preferable in terms of efficiency and correctness? Are there potential pitfalls with the single condition variable approach, such as unnecessary wake-ups or race conditions?

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