[optimization] free string memory after JSON is parsed.

native/cocos/bindings/jswrapper/v8/Object.cpp

@@ -401,13 +401,18 @@ Object *Object::createJSONObject(const ccstd::string &jsonStr) {
 }
 
 Object *Object::createJSONObject(std::u16string &&jsonStr) {
-    auto v8Str = v8::String::NewExternalTwoByte(__isolate, ccnew internal::ExternalStringResource(std::move(jsonStr)));
+    auto *external = ccnew internal::ExternalStringResource(std::move(jsonStr));
+    auto v8Str = v8::String::NewExternalTwoByte(__isolate, external);
     if (v8Str.IsEmpty()) {
         return nullptr;
     }
 
     v8::Local<v8::Context> context = __isolate->GetCurrentContext();
     v8::MaybeLocal<v8::Value> ret = v8::JSON::Parse(context, v8Str.ToLocalChecked());
+
+    // After v8::JSON::Parse, the memory of u16string could be freed.
+    external->freeMemory();
+
     if (ret.IsEmpty()) {
         return nullptr;
     }

native/cocos/bindings/jswrapper/v8/Utils.cpp

@@ -243,6 +243,28 @@ void clearPrivate(v8::Isolate *isolate, ObjectWrap &wrap) {
     }
 }
 
+// ExternalStringResource
+ExternalStringResource::ExternalStringResource(std::u16string &&s)
+: _s(std::move(s)) {
+}
+
+const uint16_t* ExternalStringResource::data() const {
+    return reinterpret_cast<const uint16_t*>(_s.data());
+}
+
+size_t ExternalStringResource::length() const {
+    return _s.length();
+}
+
+void ExternalStringResource::Dispose() {
+    delete this;
+}
+
+void ExternalStringResource::freeMemory() {
+    _s.clear();
+    _s.shrink_to_fit();
+}
+
 } // namespace internal
 } // namespace se
 

native/cocos/bindings/jswrapper/v8/Utils.h

@@ -52,24 +52,15 @@ void clearPrivate(v8::Isolate *isolate, ObjectWrap &wrap);
 
 class ExternalStringResource : public v8::String::ExternalStringResource {
 public:
-    explicit ExternalStringResource(std::u16string &&s)
-    : _s(std::move(s)) {
-
-    }
-
+    explicit ExternalStringResource(std::u16string &&s);
     ~ExternalStringResource() override = default;
 
-    const uint16_t* data() const override {
-        return reinterpret_cast<const uint16_t*>(_s.data());
-    }
+    const uint16_t* data() const override;
+    size_t length() const override;
+    void Dispose() override;
+
+    void freeMemory();
 
-    size_t length() const override {
-        return _s.length();
-    }
-
-    void Dispose() override {
-        delete this;
-    }
 private:
     std::u16string _s;
 };