{

std::lock_guard<std::mutex> lock(mutex);

task_queue.push(std::move(task), run_on_main_loop);

}

task_condition_variable.notify_one();

if (worker_threads.empty()) {

return;

}

{

std::lock_guard<std::mutex> lock(mutex);

is_shutting_down = true;

}

for (int i = 0; i < thread_count(); i++) {

task_condition_variable.notify_one();

}

for (auto& thread : worker_threads) {

if (thread.joinable()) {

thread.join();

}

}

worker_threads.clear();

is_shutting_down = false;

while (true) {

// 1. Get a valid task

pending_task task;

{

std::unique_lock<std::mutex> lock(mutex);

task_condition_variable.wait(lock, [this, &task]() { return is_shutting_down || task_queue.try_pop(task); });

if (is_shutting_down) {

return;

}

}

// 2. Do some work

task();

// 3. If all is done, notify waiters

bool all_done;

{

std::lock_guard<std::mutex> lock(mutex);

all_done = task_queue.empty();

}

if (all_done) {

all_done_condition_variable.notify_all();

}

}