Worker thread pool: Fix worker wake CV notify condition

The worker wake CV was only notified when the job queue was empty.
Now notify if the number of queued jobs is less than the number
of waiting workers.

src/worker_thread.cpp

@@ -42,7 +42,7 @@ void WorkerThreadPool::Stop()
 {
 	std::unique_lock<std::mutex> lk(this->lock);
 	this->exit = true;
-	this->empty_cv.notify_all();
+	this->worker_wait_cv.notify_all();
 	this->done_cv.wait(lk, [this]() { return this->workers == 0; });
 }
 
@@ -55,10 +55,10 @@ void WorkerThreadPool::EnqueueJob(WorkerJobFunc *func, void *data1, void *data2,
 		func(data1, data2, data3);
 		return;
 	}
-	bool notify = this->jobs.empty();
+	bool notify = this->jobs.size() < (size_t)this->workers_waiting;
 	this->jobs.push({ func, data1, data2, data3 });
 	lk.unlock();
-	if (notify) this->empty_cv.notify_one();
+	if (notify) this->worker_wait_cv.notify_one();
 }
 
 void WorkerThreadPool::Run(WorkerThreadPool *pool)
@@ -66,7 +66,9 @@ void WorkerThreadPool::Run(WorkerThreadPool *pool)
 	std::unique_lock<std::mutex> lk(pool->lock);
 	while (!pool->exit || !pool->jobs.empty()) {
 		if (pool->jobs.empty()) {
-			pool->empty_cv.wait(lk);
+			pool->workers_waiting++;
+			pool->worker_wait_cv.wait(lk);
+			pool->workers_waiting--;
 		} else {
 			WorkerJob job = pool->jobs.front();
 			pool->jobs.pop();

src/worker_thread.h

@@ -30,10 +30,11 @@ private:
 	};
 
 	uint workers = 0;
+	uint workers_waiting = 0;
 	bool exit = false;
 	std::mutex lock;
 	std::queue<WorkerJob> jobs;
-	std::condition_variable empty_cv;
+	std::condition_variable worker_wait_cv;
 	std::condition_variable done_cv;
 
 	static void Run(WorkerThreadPool *pool);