Add JSI method for adjusting external memory size

packages/react-native/ReactCommon/jsc/JSCRuntime.cpp

@@ -233,6 +233,7 @@ class JSCRuntime : public jsi::Runtime {
   bool strictEquals(const jsi::String& a, const jsi::String& b) const override;
   bool strictEquals(const jsi::Object& a, const jsi::Object& b) const override;
   bool instanceOf(const jsi::Object& o, const jsi::Function& f) override;
+  void setExternalMemoryPressure(const jsi::Object&, size_t) override;
 
  private:
   // Basically convenience casts
@@ -1392,6 +1393,8 @@ bool JSCRuntime::instanceOf(const jsi::Object& o, const jsi::Function& f) {
   return res;
 }
 
+void JSCRuntime::setExternalMemoryPressure(const jsi::Object&, size_t) {}
+
 jsi::Runtime::PointerValue* JSCRuntime::makeSymbolValue(
     JSValueRef symbolRef) const {
 #ifndef NDEBUG

packages/react-native/ReactCommon/jsi/jsi/decorator.h

@@ -252,6 +252,10 @@ class RuntimeDecorator : public Base, private jsi::Instrumentation {
     plain_.setNativeState(o, state);
   }
 
+  void setExternalMemoryPressure(const Object& obj, size_t amt) override {
+    plain_.setExternalMemoryPressure(obj, amt);
+  }
+
   Value getProperty(const Object& o, const PropNameID& name) override {
     return plain_.getProperty(o, name);
   };

packages/react-native/ReactCommon/jsi/jsi/jsi-inl.h

@@ -227,6 +227,11 @@ inline void Object::setNativeState(
   runtime.setNativeState(*this, state);
 }
 
+inline void Object::setExternalMemoryPressure(Runtime& runtime, size_t amt)
+    const {
+  runtime.setExternalMemoryPressure(*this, amt);
+}
+
 inline Array Object::getPropertyNames(Runtime& runtime) const {
   return runtime.getPropertyNames(*this);
 }

packages/react-native/ReactCommon/jsi/jsi/jsi.h

@@ -387,6 +387,11 @@ class JSI_EXPORT Runtime {
 
   virtual bool instanceOf(const Object& o, const Function& f) = 0;
 
+  /// See Object::setExternalMemoryPressure.
+  virtual void setExternalMemoryPressure(
+      const jsi::Object& obj,
+      size_t amount) = 0;
+
   // These exist so derived classes can access the private parts of
   // Value, Symbol, String, and Object, which are all friends of Runtime.
   template <typename T>
@@ -834,6 +839,16 @@ class JSI_EXPORT Object : public Pointer {
   /// works.  I only need it in one place.)
   Array getPropertyNames(Runtime& runtime) const;
 
+  /// Inform the runtime that there is additional memory associated with a given
+  /// JavaScript object that is not visible to the GC. This can be used if an
+  /// object is known to retain some native memory, and may be used to guide
+  /// decisions about when to run garbage collection.
+  /// This method may be invoked multiple times on an object, and subsequent
+  /// calls will overwrite any previously set value. Once the object is garbage
+  /// collected, the associated external memory will be considered freed and may
+  /// no longer factor into GC decisions.
+  void setExternalMemoryPressure(Runtime& runtime, size_t amt) const;
+
  protected:
   void setPropertyValue(
       Runtime& runtime,