WorkerThreadPool: Improve logic

- The main thread function and the collaborative wait functions have a much more similar structure than earlier, which yields (pun intended) better maintainability.
- Also, there are not assertions anymore about the reason for ending a wait being valid, because spurious awakes can happen and so the assert would fail without that indicating an issue.

core/object/worker_thread_pool.cpp

@@ -180,13 +180,16 @@ void WorkerThreadPool::_process_task(Task *p_task) {
 
 void WorkerThreadPool::_thread_function(void *p_user) {
 	ThreadData *thread_data = (ThreadData *)p_user;
+
 	while (true) {
 		Task *task_to_process = nullptr;
 		{
 			MutexLock lock(singleton->task_mutex);
-			if (singleton->exit_threads) {
-				return;
+
+			if (unlikely(singleton->exit_threads)) {
+				break;
 			}
+
 			thread_data->signaled = false;
 
 			if (singleton->task_queue.first()) {
@@ -194,7 +197,6 @@ void WorkerThreadPool::_thread_function(void *p_user) {
 				singleton->task_queue.remove(singleton->task_queue.first());
 			} else {
 				thread_data->cond_var.wait(lock);
-				DEV_ASSERT(singleton->exit_threads || thread_data->signaled);
 			}
 		}
 
@@ -442,22 +444,33 @@ void WorkerThreadPool::_unlock_unlockable_mutexes() {
 void WorkerThreadPool::_wait_collaboratively(ThreadData *p_caller_pool_thread, Task *p_task) {
 	// Keep processing tasks until the condition to stop waiting is met.
 
-#define IS_WAIT_OVER (unlikely(p_task == ThreadData::YIELDING) ? p_caller_pool_thread->yield_is_over : p_task->completed)
-
 	while (true) {
 		Task *task_to_process = nullptr;
 		bool relock_unlockables = false;
 		{
 			MutexLock lock(task_mutex);
+
 			bool was_signaled = p_caller_pool_thread->signaled;
 			p_caller_pool_thread->signaled = false;
 
-			if (IS_WAIT_OVER) {
-				if (unlikely(p_task == ThreadData::YIELDING)) {
+			if (unlikely(exit_threads)) {
+				break;
+			}
+
+			bool wait_is_over = false;
+			if (unlikely(p_task == ThreadData::YIELDING)) {
+				if (p_caller_pool_thread->yield_is_over) {
 					p_caller_pool_thread->yield_is_over = false;
+					wait_is_over = true;
 				}
+			} else {
+				if (p_task->completed) {
+					wait_is_over = true;
+				}
+			}
 
-				if (!exit_threads && was_signaled) {
+			if (wait_is_over) {
+				if (was_signaled) {
 					// This thread was awaken for some additional reason, but it's about to exit.
 					// Let's find out what may be pending and forward the requests.
 					uint32_t to_process = task_queue.first() ? 1 : 0;
@@ -472,28 +485,26 @@ void WorkerThreadPool::_wait_collaboratively(ThreadData *p_caller_pool_thread, T
 				break;
 			}
 
-			if (!exit_threads) {
-				if (p_caller_pool_thread->current_task->low_priority && low_priority_task_queue.first()) {
-					if (_try_promote_low_priority_task()) {
-						_notify_threads(p_caller_pool_thread, 1, 0);
-					}
+			if (p_caller_pool_thread->current_task->low_priority && low_priority_task_queue.first()) {
+				if (_try_promote_low_priority_task()) {
+					_notify_threads(p_caller_pool_thread, 1, 0);
 				}
+			}
 
-				if (singleton->task_queue.first()) {
-					task_to_process = task_queue.first()->self();
-					task_queue.remove(task_queue.first());
-				}
+			if (singleton->task_queue.first()) {
+				task_to_process = task_queue.first()->self();
+				task_queue.remove(task_queue.first());
+			}
 
-				if (!task_to_process) {
-					p_caller_pool_thread->awaited_task = p_task;
+			if (!task_to_process) {
+				p_caller_pool_thread->awaited_task = p_task;
 
-					_unlock_unlockable_mutexes();
-					relock_unlockables = true;
-					p_caller_pool_thread->cond_var.wait(lock);
+				_unlock_unlockable_mutexes();
+				relock_unlockables = true;
 
-					DEV_ASSERT(exit_threads || p_caller_pool_thread->signaled || IS_WAIT_OVER);
-					p_caller_pool_thread->awaited_task = nullptr;
-				}
+				p_caller_pool_thread->cond_var.wait(lock);
+
+				p_caller_pool_thread->awaited_task = nullptr;
 			}
 		}