add EMode to WorkerTheadPool to avoid thread starvation (#492)

- Improvement: Add a new mode to worker thread pools to avoid starvation of workers which could cause long stalls due to other work begin queued up. UE-305498

1 files changed, 12 insertions, 11 deletions

diff --git a/src/zencore/include/zencore/workthreadpool.h b/src/zencore/include/zencore/workthreadpool.h
index 62356495c..4c38dd651 100644
--- a/src/zencore/include/zencore/workthreadpool.h
+++ b/src/zencore/include/zencore/workthreadpool.h
@@ -18,11 +18,7 @@ struct IWork : public RefCounted
 {
 	virtual void Execute() = 0;
 
-	inline std::exception_ptr GetException() { return m_Exception; }
-
 private:
-	std::exception_ptr m_Exception;
-
 	friend class WorkerThreadPool;
 };
 
@@ -35,13 +31,18 @@ public:
 	WorkerThreadPool(int InThreadCount, std::string_view WorkerThreadBaseName);
 	~WorkerThreadPool();
 
-	void ScheduleWork(Ref<IWork> Work);
-	void ScheduleWork(std::function<void()>&& Work);
+	// Decides what to do if there are no free workers in the pool when the work is submitted
+	enum class EMode
+	{
+		EnableBacklog,	// The work will be added to a backlog of work to do
+		DisableBacklog	// The work will be executed synchronously in the caller thread
+	};
+
+	void ScheduleWork(Ref<IWork> Work, EMode Mode);
+	void ScheduleWork(std::function<void()>&& Work, EMode Mode);
 
 	template<typename Func>
-	auto EnqueueTask(std::packaged_task<Func> Task);
-
-	[[nodiscard]] size_t PendingWorkItemCount() const;
+	auto EnqueueTask(std::packaged_task<Func> Task, EMode Mode);
 
 private:
 	struct Impl;
@@ -54,7 +55,7 @@ private:
 
 template<typename Func>
 auto
-WorkerThreadPool::EnqueueTask(std::packaged_task<Func> Task)
+WorkerThreadPool::EnqueueTask(std::packaged_task<Func> Task, EMode Mode)
 {
 	struct FutureWork : IWork
 	{
@@ -67,7 +68,7 @@ WorkerThreadPool::EnqueueTask(std::packaged_task<Func> Task)
 	Ref<FutureWork> Work{new FutureWork(std::move(Task))};
 
 	auto Future = Work->m_Task.get_future();
-	ScheduleWork(std::move(Work));
+	ScheduleWork(std::move(Work), Mode);
 	return Future;
 }