diff --git a/include/UECS/EntityMngr.h b/include/UECS/EntityMngr.h
index f4f99c4..a09bf79 100644
--- a/include/UECS/EntityMngr.h
+++ b/include/UECS/EntityMngr.h
@@ -112,9 +112,13 @@ namespace Ubpa::UECS {
 		const std::set<Archetype*>& QueryArchetypes(const EntityQuery&) const;
 		mutable std::unordered_map<EntityQuery, std::set<Archetype*>> queryCache;
 
+		// if job is nullptr, direct run
 		void GenEntityJob(World*, Job*, SystemFunc*) const;
+		// if job is nullptr, direct run
 		void GenChunkJob(World*, Job*, SystemFunc*) const;
+		// if job is nullptr, direct run
 		void GenJob(World*, Job*, SystemFunc*) const;
+		// if job is nullptr, direct run
 		void AutoGen(World*, Job*, SystemFunc*) const;
 
 		struct EntityInfo {
diff --git a/src/core/EntityMngr.cpp b/src/core/EntityMngr.cpp
index afb340e..3a7c3d2 100644
--- a/src/core/EntityMngr.cpp
+++ b/src/core/EntityMngr.cpp
@@ -268,6 +268,7 @@ void EntityMngr::GenEntityJob(World* w, Job* job, SystemFunc* sys) const {
 		return;
 	
 	if (sys->IsParallel()) {
+		assert(job);
 		size_t indexOffsetInQuery = 0;
 		for (Archetype* archetype : QueryArchetypes(sys->entityQuery)) {
 			auto [chunkEntity, chunkCmpts, sizes] = archetype->Locate(sys->entityQuery.locator);
@@ -281,12 +282,13 @@ void EntityMngr::GenEntityJob(World* w, Job* job, SystemFunc* sys) const {
 					size_t idxOffsetInChunk = i * chunkCapacity;
 					size_t indexOffsetInQueryChunk = indexOffsetInQuery + idxOffsetInChunk;
 					CmptsView chunkView{ cmpts.data(), cmpts.size() };
+					SingletonsView singletonsView{ singletons.data(), singletons.size() };
 
 					size_t J = min(chunkCapacity, num - idxOffsetInChunk);
 					for (size_t j = 0; j < J; j++) {
 						(*sys)(
 							w,
-							SingletonsView{ singletons.data(), singletons.size() },
+							singletonsView,
 							entities[j],
 							indexOffsetInQueryChunk + j,
 							chunkView
@@ -301,7 +303,7 @@ void EntityMngr::GenEntityJob(World* w, Job* job, SystemFunc* sys) const {
 		}
 	}
 	else {
-		job->emplace([this, singletons = std::move(singletons), sys, w]() {
+		auto work = [this, singletons = std::move(singletons), sys, w]() {
 			size_t indexOffsetInQuery = 0;
 			for (Archetype* archetype : QueryArchetypes(sys->entityQuery)) {
 				auto [chunkEntity, chunkCmpts, sizes] = archetype->Locate(sys->entityQuery.locator);
@@ -314,16 +316,17 @@ void EntityMngr::GenEntityJob(World* w, Job* job, SystemFunc* sys) const {
 					size_t idxOffsetInChunk = i * chunkCapacity;
 					size_t indexOffsetInQueryChunk = indexOffsetInQuery + idxOffsetInChunk;
 					CmptsView chunkView{ chunkCmpts[i].data(), chunkCmpts[i].size() };
+					SingletonsView singletonsView{ singletons.data(), singletons.size() };
 
 					size_t J = min(chunkCapacity, num - idxOffsetInChunk);
 					for (size_t j = 0; j < J; j++) {
 						(*sys)(
 							w,
-							SingletonsView{ singletons.data(), singletons.size() },
+							singletonsView,
 							chunkEntity[i][j],
 							indexOffsetInQueryChunk + j,
 							chunkView
-						);
+							);
 						for (size_t k = 0; k < chunkCmpts[i].size(); k++)
 							reinterpret_cast<uint8_t*&>(chunkCmpts[i][k].p) += sizes[k];
 					}
@@ -331,7 +334,12 @@ void EntityMngr::GenEntityJob(World* w, Job* job, SystemFunc* sys) const {
 
 				indexOffsetInQuery += num;
 			}
-		});
+		};
+
+		if (job)
+			job->emplace(std::move(work));
+		else
+			work();
 	}
 }
 
@@ -343,14 +351,16 @@ void EntityMngr::GenChunkJob(World* w, Job* job, SystemFunc* sys) const {
 		return;
 
 	if (sys->IsParallel()) {
+		assert(job != nullptr);
 		for (Archetype* archetype : QueryArchetypes(sys->entityQuery)) {
 			size_t chunkNum = archetype->ChunkNum();
+			SingletonsView singletonsView{ singletons.data(), singletons.size() };
 
 			for (size_t i = 0; i < chunkNum; i++) {
 				job->emplace([=, singletons = singletons]() {
 					(*sys)(
 						w,
-						SingletonsView{ singletons.data(), singletons.size() },
+						singletonsView,
 						ChunkView{ archetype, i }
 					);
 				});
@@ -358,7 +368,7 @@ void EntityMngr::GenChunkJob(World* w, Job* job, SystemFunc* sys) const {
 		}
 	}
 	else {
-		job->emplace([this, w, sys, singletons = std::move(singletons)]() {
+		auto work = [this, w, sys, singletons = std::move(singletons)]() {
 			for (Archetype* archetype : QueryArchetypes(sys->entityQuery)) {
 				size_t chunkNum = archetype->ChunkNum();
 				SingletonsView singletonsView{ singletons.data(), singletons.size() };
@@ -371,7 +381,12 @@ void EntityMngr::GenChunkJob(World* w, Job* job, SystemFunc* sys) const {
 					);
 				}
 			}
-		});
+		};
+
+		if (job)
+			job->emplace(std::move(work));
+		else
+			work();
 	}
 }
 
@@ -382,12 +397,17 @@ void EntityMngr::GenJob(World* w, Job* job, SystemFunc* sys) const {
 	if (!success)
 		return;
 
-	job->emplace([=, singletons = std::move(singletons)]() {
+	auto work = [=, singletons = std::move(singletons)]() {
 		(*sys)(
 			w,
 			SingletonsView{ singletons.data(), singletons.size() }
 		);
-	});
+	};
+
+	if (job)
+		job->emplace(std::move(work));
+	else
+		work();
 }
 
 void EntityMngr::AutoGen(World* w, Job* job, SystemFunc* sys) const {
diff --git a/src/core/World.cpp b/src/core/World.cpp
index 621ba94..be78adc 100644
--- a/src/core/World.cpp
+++ b/src/core/World.cpp
@@ -45,10 +45,14 @@ string World::DumpUpdateJobGraph() const {
 }
 
 void World::Run(SystemFunc* sys) {
-	Job job;
-	JobExecutor executor;
-	entityMngr.AutoGen(this, &job, sys);
-	executor.run(job).wait();
+	if (sys->IsParallel()) {
+		Job job;
+		JobExecutor executor;
+		entityMngr.AutoGen(this, &job, sys);
+		executor.run(job).wait();
+	}
+	else
+		entityMngr.AutoGen(this, nullptr, sys);
 }
 
 // after running Update