Function steal_task

src/threadpool_scheduler.cpp:149–170

Try to steal a task from another thread's queue

// Try to steal a task from another thread's queue
static task_run_handle steal_task(threadpool_data* impl, std::size_t thread_id)
{
	// Make a list of victim thread ids and shuffle it
	std::vector<std::size_t> victims(impl->thread_data.size());
	std::iota(victims.begin(), victims.end(), 0);
	std::shuffle(victims.begin(), victims.end(), impl->thread_data[thread_id].rng);

	// Try to steal from another thread
	for (std::size_t i: victims) {
		// Don't try to steal from ourself
		if (i == thread_id)
			continue;

		if (task_run_handle t = impl->thread_data[i].queue.steal())
			return t;
	}

	// No tasks found, but we might have missed one if it was just added. In
	// practice this doesn't really matter since it will be handled by another
	// thread.
	return task_run_handle();
}

// Main task stealing loop which is used by worker threads when they have
// nothing to do.