Producer - Consumer Queue

Consider the following code for a queue with multiple producers and consumers. The close() function is guaranteed to be called exactly once by the user code, and enqueue() will not be called after that. dequeue() is supposed to block if the queue is empty and to return an empty optional if the queue is closed and all the elements have been dequeued. Which of the following are true? Give a short explanation.

• [2023 - No.1] // place 4 & stmt 2
• [2023 - No.2] // place 3 & stmt 1

Futures

Consider the following code for implementing a future mechanism (the set() function is guaranteed to be called exactly once by the user code). Which of the following are true? Give a short explanation.

• [2023 - No.3] // cv.notify_all(); → lock
• [2023 - No.4] // lock → cv.notify_all();

Continuations

Consider the following code for enqueueing a continuation on a future (the set() function is guaranteed to be called exactly once but he user code). Which of the following are true? Give a short explanation.

• [2023 - No.5] // set → val = v; lck.unlock();
• [2023 - No.6] // set val = v; → unique_lock<mutex> lck(mtx);
• [2022 - No.6] // set val = v; → unique_lock<mutex> lck(mtx); // unique_lock<mutex> lck(mtx); continuations.push_back(f);

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