Attention: Here be dragons

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スレッドセーフAPI

スレッド

スレッドは、CPU とコア間で処理能力のバランスを取るために使用されます。Godot はマルチスレッドをサポートしていますが、エンジン全体ではサポートしていません。

以下は、Godotのさまざまな領域でマルチスレッドを使用する方法の一覧です。

グローバル スコープ

Most Global Scope singletons are thread-safe by default. Accessing servers from threads is supported. However, for the rendering and physics servers, thread-safe operation must be enabled in the project settings first.

This makes singletons ideal for code that creates dozens of thousands of instances in servers and controls them from threads. Of course, it requires a bit more code, as this is used directly and not within the scene tree.

シーンツリー

Interacting with the active scene tree is not thread-safe. Make sure to use mutexes when sending data between threads. If you want to call functions or set properties from a thread, you may use call_deferred or set_deferred:

GDScriptC#

# Unsafe:
node.add_child(child_node)
# Safe:
node.add_child.call_deferred(child_node)

ただし、アクティブなツリーの外側にシーンチャンク(ツリー配置のノード)を作成することは問題ありません。このようにして、シーンの一部をスレッドで構築またはインスタンス化し、メインスレッドに追加できます:

GDScriptC#

var enemy_scene = load("res://enemy_scene.scn")
var enemy = enemy_scene.instantiate()
enemy.add_child(weapon) # Set a weapon.
world.add_child.call_deferred(enemy)

Still, this is only really useful if you have one thread loading data. Attempting to load or create scene chunks from multiple threads may work, but you risk resources (which are only loaded once in Godot) being tweaked by the multiple threads, resulting in unexpected behaviors or crashes.

自分が何をしているかを本当に知っていて、単一のリソースが複数のリソースで使用または設定されていないことが確実な場合にのみ、複数のスレッドを使用してシーンデータを生成できます。それ以外の場合は、サーバーAPI(完全にスレッドセーフ)を直接使用するだけにとどめ、シーンやリソースに触れない方が安全です。

レンダリング

Instancing nodes that render anything in 2D or 3D (such as Sprite2D or MeshInstance3D) is not thread-safe by default. To run the rendering driver on a separate thread, set the Rendering > Driver > Thread Model project setting to Separate.

Note that the Separate thread model has several known bugs, so it may not be usable in all scenarios.

警告

You should avoid calling functions involving direct interaction with the GPU on other threads, such as creating new textures or modifying and retrieving image data. These operations can lead to performance stalls because they require synchronization with the RenderingServer, as data needs to be transmitted to or updated on the GPU.

物理

Physics simulation is not thread-safe by default. To run the physics servers on separate threads (making them thread-safe), enable the following project settings:

• PhysicsServer2D: Physics > 2D > Run on Separate Thread.

• PhysicsServer3D: Physics > 3D > Run on Separate Thread.

ナビゲーション

NavigationServer2D and NavigationServer3D are both thread-safe and thread-friendly.

The navigation-related query functions can be called by threads and run in true parallel.

By default, a conservative number of threads is supported running in true parallel on navigation maps before additional threads have to wait for map data access at a semaphore. To increase the number of threads that can run simultaneously on map data, set Navigation > Pathfinding > Max Threads.

The navigation server-related resources like NavigationSourceGeometryData, NavigationMesh, and NavigationPolygon are all thread-safe but not necessarily thread-friendly. They use internal read-write locks for thread-safety so editing the same resource (e.g. a single big navmesh) on multiple threads at the same time can cause thread congestion.

The navigation-related helper classes like AStar2D, AStar3D, and AStarGrid2D are not thread-safe. They can be used with threads to some limited capacity, but using two or more threads on the same AStar object causes corruption. For example, using a dedicated background thread per AStar object to populate points or do queries works, but two threads using the same AStar object would corrupt each other's data.

GDScript arrays and dictionaries

In GDScript, reading and writing elements from multiple threads is OK, but anything that changes the container size (resizing, adding, or removing elements) requires locking a mutex.

リソース

Modifying a unique resource from multiple threads is not supported. However, handling references on multiple threads is supported. Hence loading resources on a thread is as well - scenes, textures, meshes, etc - can be loaded and manipulated on a thread and then added to the active scene on the main thread. The limitation here is as described above: one must be careful not to load the same resource from multiple threads at once. Therefore, it's easiest to use one thread for loading and modifying resources, and then the main thread for adding them.