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03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Blueprint/BlueprintThreadSafe/BlueprintThreadSafe.md

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+# BlueprintThreadSafe
+
+- **功能描述：** 用在类上或函数上，标记类里的函数都是线程安全的。
+这样就可以在动画蓝图等非游戏线程被调用了。
+- **使用位置：** UCLASS, UFUNCTION
+- **引擎模块：** Blueprint
+- **元数据类型：** bool
+- **限制类型：** 从实践上，类一般是BlueprintFunctionLibrary
+- **关联项：** [NotBlueprintThreadSafe](../NotBlueprintThreadSafe.md)
+- **常用程度：** ★★★
+
+动画蓝图的AimGraph默认是开启线程安全Update的。设置在ClassSettings里（默认是打开的）
+
+![Untitled](Untitled.png)
+
+可参考官方文档的**CPU Thread Usage and Performance这一节**
+
+[Graphing in Animation Blueprints](https://docs.unrealengine.com/5.3/en-US/graphing-in-animation-blueprints-in-unreal-engine/#cputhreadusageandperformance)
+
+因此AimGraph里的函数要求都得是线程安全的。你的C++函数或者是蓝图里蓝图库里的函数都需要手动标记为ThreadSafe，默认不带ThreadSafe标记的都是不线程安全的。
+
+在蓝图里，如果在蓝图函数面板中勾上ThreadSafe，这个函数的对象会设置bThreadSafe=True，从而在编译生成的BlueprintGeneratedClass上面设置(BlueprintThreadSafe = true)
+
+![Untitled](Untitled%201.png)
+
+## 测试蓝图函数库：
+
+同样的函数，一个打开ThreadSafe，一个没有。没有的那个函数在动画蓝图的AnimGraph里使用的时候，在编译的时候就会触发警告。
+
+![Untitled](Untitled%202.png)
+
+测试结果：
+
+![Untitled](Untitled%203.png)
+
+## 在C++里，C++的测试代码：
+
+```cpp
+//(BlueprintThreadSafe = , IncludePath = Class/Blueprint/MyClass_ThreadSafe.h, ModuleRelativePath = Class/Blueprint/MyClass_ThreadSafe.h)
+UCLASS(meta=(BlueprintThreadSafe))
+class INSIDER_API UMyBlueprintFunctionLibrary_ThreadSafe : public UBlueprintFunctionLibrary
+{
+	GENERATED_BODY()
+public:
+	UFUNCTION(BlueprintPure)
+	static float MyFunc_ClassThreadSafe_Default(float value) {return value+100;}
+
+	//(ModuleRelativePath = Class/Blueprint/MyClass_ThreadSafe.h, NotBlueprintThreadSafe = )
+	UFUNCTION(BlueprintPure,meta=(NotBlueprintThreadSafe))
+	static float MyFunc_ClassThreadSafe_FuncNotThreadSafe(float value) {return value+100;}
+};
+
+UCLASS()
+class INSIDER_API UMyBlueprintFunctionLibrary_NoThreadSafe : public UBlueprintFunctionLibrary
+{
+	GENERATED_BODY()
+public:
+	//(BlueprintThreadSafe = , ModuleRelativePath = Class/Blueprint/MyClass_ThreadSafe.h)
+	UFUNCTION(BlueprintPure,meta=(BlueprintThreadSafe))
+	static float MyFunc_ClassDefault_FuncThreadSafe(float value) {return value+100;}
+
+	//(ModuleRelativePath = Class/Blueprint/MyClass_ThreadSafe.h, NotBlueprintThreadSafe = )
+	UFUNCTION(BlueprintPure,meta=(NotBlueprintThreadSafe))
+	static float MyFunc_ClassDefault_FuncNotThreadSafe(float value) {return value+100;}
+};
+
+UCLASS()
+class INSIDER_API UMyBlueprintFunctionLibrary_Default : public UBlueprintFunctionLibrary
+{
+	GENERATED_BODY()
+public:
+	UFUNCTION(BlueprintPure)
+	static float MyFunc_ClassDefault_FuncDefault(float value) {return value+100;}
+};
+```
+
+## 动画蓝图的测试效果：
+
+![Untitled](Untitled%204.png)
+
+## 解析原理：
+
+```cpp
+bool FBlueprintEditorUtils::HasFunctionBlueprintThreadSafeMetaData(const UFunction* InFunction)
+{
+	if(InFunction)
+	{
+		const bool bHasThreadSafeMetaData = InFunction->HasMetaData(FBlueprintMetadata::MD_ThreadSafe);
+		const bool bHasNotThreadSafeMetaData = InFunction->HasMetaData(FBlueprintMetadata::MD_NotThreadSafe);
+		const bool bClassHasThreadSafeMetaData = InFunction->GetOwnerClass() && InFunction->GetOwnerClass()->HasMetaData(FBlueprintMetadata::MD_ThreadSafe);
+
+		// Native functions need to just have the correct class/function metadata
+		const bool bThreadSafeNative = InFunction->HasAnyFunctionFlags(FUNC_Native) && (bHasThreadSafeMetaData || (bClassHasThreadSafeMetaData && !bHasNotThreadSafeMetaData));
+
+		// Script functions get their flag propagated from their entry point, and dont pay heed to class metadata
+		const bool bThreadSafeScript = !InFunction->HasAnyFunctionFlags(FUNC_Native) && bHasThreadSafeMetaData;
+		
+		return bThreadSafeNative || bThreadSafeScript;
+	}
+	
+	return false;
+}
+```
+
+可以从逻辑上看出，如果在UCLASS上带上了BlueprintThreadSafe，则其内部的函数就默认是线程安全，除非特意手动加上NotBlueprintThreadSafe来排除。而如果UCLASS上没有标记，则需一个个手动的在UFUNCTION上标记BlueprintThreadSafe。两种方式都可以。
+
+注意UCLASS(meta=(NotBlueprintThreadSafe))这种是没有被识别判断的，因此并没有什么意义。