Implement parallel foreach() for easier multithreading

core/object/worker_thread_pool.h

@@ -202,4 +202,25 @@ public:
 	~WorkerThreadPool();
 };
 
+template <typename F>
+static _FORCE_INLINE_ void for_range(int i_begin, int i_end, bool parallel, String name, F f) {
+	if (!parallel) {
+		for (int i = i_begin; i < i_end; i++) {
+			f(i);
+		}
+		return;
+	}
+
+	auto wrapper = [&](int i, void *unused) {
+		f(i + i_begin);
+	};
+
+	WorkerThreadPool *wtp = WorkerThreadPool::get_singleton();
+	WorkerThreadPool::GroupID gid = wtp->add_template_group_task(
+			&wrapper, &decltype(wrapper)::operator(), nullptr,
+			i_end - i_begin, -1,
+			true, name);
+	wtp->wait_for_group_task_completion(gid);
+}
+
 #endif // WORKER_THREAD_POOL_H

modules/raycast/raycast_occlusion_cull.cpp

@@ -354,41 +354,14 @@ void RaycastOcclusionCull::Scenario::_update_dirty_instance(int p_idx, RID *p_in
 	// Embree requires the last element to be readable by a 16-byte SSE load instruction, so we add padding to be safe.
 	occ_inst->xformed_vertices.resize(vertices_size + 1);
 
-	const Vector3 *read_ptr = occ->vertices.ptr();
-	Vector3 *write_ptr = occ_inst->xformed_vertices.ptr();
-
-	if (vertices_size > 1024) {
-		TransformThreadData td;
-		td.xform = occ_inst->xform;
-		td.read = read_ptr;
-		td.write = write_ptr;
-		td.vertex_count = vertices_size;
-		td.thread_count = WorkerThreadPool::get_singleton()->get_thread_count();
-		WorkerThreadPool::GroupID group_task = WorkerThreadPool::get_singleton()->add_template_group_task(this, &Scenario::_transform_vertices_thread, &td, td.thread_count, -1, true, SNAME("RaycastOcclusionCull"));
-		WorkerThreadPool::get_singleton()->wait_for_group_task_completion(group_task);
-
-	} else {
-		_transform_vertices_range(read_ptr, write_ptr, occ_inst->xform, 0, vertices_size);
-	}
+	for_range(0, vertices_size, vertices_size > 1024, SNAME("RaycastOcclusionCull"), [&](const int i) {
+		occ_inst->xformed_vertices[i] = occ_inst->xform.xform(occ->vertices[i]);
+	});
 
 	occ_inst->indices.resize(occ->indices.size());
 	memcpy(occ_inst->indices.ptr(), occ->indices.ptr(), occ->indices.size() * sizeof(int32_t));
 }
 
-void RaycastOcclusionCull::Scenario::_transform_vertices_thread(uint32_t p_thread, TransformThreadData *p_data) {
-	uint32_t vertex_total = p_data->vertex_count;
-	uint32_t total_threads = p_data->thread_count;
-	uint32_t from = p_thread * vertex_total / total_threads;
-	uint32_t to = (p_thread + 1 == total_threads) ? vertex_total : ((p_thread + 1) * vertex_total / total_threads);
-	_transform_vertices_range(p_data->read, p_data->write, p_data->xform, from, to);
-}
-
-void RaycastOcclusionCull::Scenario::_transform_vertices_range(const Vector3 *p_read, Vector3 *p_write, const Transform3D &p_xform, int p_from, int p_to) {
-	for (int i = p_from; i < p_to; i++) {
-		p_write[i] = p_xform.xform(p_read[i]);
-	}
-}
-
 void RaycastOcclusionCull::Scenario::_commit_scene(void *p_ud) {
 	Scenario *scenario = (Scenario *)p_ud;
 	int commit_idx = 1 - (scenario->current_scene_idx);

modules/raycast/raycast_occlusion_cull.h

@@ -121,14 +121,6 @@ private:
 			const uint32_t *masks;
 		};
 
-		struct TransformThreadData {
-			uint32_t thread_count;
-			uint32_t vertex_count;
-			Transform3D xform;
-			const Vector3 *read;
-			Vector3 *write = nullptr;
-		};
-
 		Thread *commit_thread = nullptr;
 		bool commit_done = true;
 		bool dirty = false;
@@ -144,8 +136,6 @@ private:
 
 		void _update_dirty_instance_thread(int p_idx, RID *p_instances);
 		void _update_dirty_instance(int p_idx, RID *p_instances);
-		void _transform_vertices_thread(uint32_t p_thread, TransformThreadData *p_data);
-		void _transform_vertices_range(const Vector3 *p_read, Vector3 *p_write, const Transform3D &p_xform, int p_from, int p_to);
 		static void _commit_scene(void *p_ud);
 		bool update();
 

tests/core/threads/test_worker_thread_pool.h

@@ -106,6 +106,32 @@ TEST_CASE("[WorkerThreadPool] Process elements using group tasks") {
 	}
 }
 
+TEST_CASE("[WorkerThreadPool] Parallel foreach") {
+	const int count_max = 256;
+
+	for (int midpoint = 0; midpoint < count_max; midpoint++) {
+		LocalVector<int> c;
+		c.resize(count_max);
+
+		for_range(0, count_max, true, String(), [&](int i) {
+			c[i] = 1;
+		});
+		c.sort();
+		CHECK(c[0] == 1);
+		CHECK(c[0] == c[count_max - 1]);
+
+		for_range(0, midpoint, false, String(), [&](int i) {
+			c[i]++;
+		});
+		for_range(midpoint, count_max, true, String(), [&](int i) {
+			c[i]++;
+		});
+		c.sort();
+		CHECK(c[0] == 2);
+		CHECK(c[0] == c[count_max - 1]);
+	}
+}
+
 } // namespace TestWorkerThreadPool
 
 #endif // TEST_WORKER_THREAD_POOL_H