commit ce71348a09f6689dd01a68db64b172191d0182d8
Author: Andrey Kosyakov <caseq@chromium.org>
Date: Thu Dec 21 18:38:38 2023 +0000
[bindings] Use v8::Array::Iterate for converting script wrappables
This changes CreateIDLSequenceFromV8Array to use the new
v8::Array::Iterate() operation.
This speeds up the "execBundles" part of the microbenchmark
at crbug.com/dawn/1858 by around 3x.
This depends on crrev.com/c/4846594 landing (and rolling) first.
This is a slight re-work of https://crrev.com/c/4847447/3,
originally by jkummerow@chromium.org
Bug: v8:14218, dawn:1858, 1511239
Change-Id: Ia266556d05b4d53e6942e12609d1c08882b4ff0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5132129
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1240236}
diff --git a/third_party/blink/renderer/bindings/core/v8/native_value_traits.h b/third_party/blink/renderer/bindings/core/v8/native_value_traits.h
index 1e5a0790df6da..a5c28b37e9454 100644
--- a/third_party/blink/renderer/bindings/core/v8/native_value_traits.h
+++ b/third_party/blink/renderer/bindings/core/v8/native_value_traits.h
@@ -84,6 +84,12 @@ struct NativeValueTraitsBase {
std::is_pointer_v<ImplType> ||
requires(ImplType value) { value.IsNull(); };
+ // This should only be true for certain subclasses of ScriptWrappable
+ // that satisfy the assumptions of CreateIDLSequenceFromV8ArraySlow() with
+ // regards to how NativeValue() is implemented for the underlying type.
+ static constexpr bool supports_scriptwrappable_specific_fast_array_iteration =
+ false;
+
template <typename... ExtraArgs>
static decltype(auto) ArgumentValue(v8::Isolate* isolate,
int argument_index,
diff --git a/third_party/blink/renderer/bindings/core/v8/native_value_traits_impl.h b/third_party/blink/renderer/bindings/core/v8/native_value_traits_impl.h
index 5011503dcf1c0..f085b6e905161 100644
--- a/third_party/blink/renderer/bindings/core/v8/native_value_traits_impl.h
+++ b/third_party/blink/renderer/bindings/core/v8/native_value_traits_impl.h
@@ -1037,10 +1037,86 @@ CreateIDLSequenceFromV8ArraySlow(v8::Isolate* isolate,
return {};
}
- typename NativeValueTraits<IDLSequence<T>>::ImplType result;
+ using ResultType = typename NativeValueTraits<IDLSequence<T>>::ImplType;
+ ResultType result;
result.ReserveInitialCapacity(length);
v8::Local<v8::Context> current_context = isolate->GetCurrentContext();
v8::TryCatch try_block(isolate);
+
+ // Fast path -- we're creating a sequence of script wrappables, which can be
+ // done by directly getting underlying object as long as array types are
+ // homogeneous. With ScriptWrappables, we don't expect to enter JS during
+ // iteration, so we can rely on v8::Array::Iterate() which is much faster than
+ // iterating an array on the client side of the v8. Additionally, for most
+ // subsptyes of ScriptWrappables, we can speed up type checks (see more on
+ // that below next to supports_scriptwrappable_specific_fast_array_iteration
+ // check.
+ if constexpr (std::is_base_of_v<ScriptWrappable, T>) {
+ struct CallbackData {
+ STACK_ALLOCATED();
+
+ public:
+ v8::Isolate* isolate;
+ v8::TypecheckWitness witness;
+ ResultType& result;
+ ExceptionState& exception_state;
+ CallbackData(v8::Isolate* isolate,
+ ResultType& result,
+ ExceptionState& exception_state)
+ : isolate(isolate),
+ witness(isolate),
+ result(result),
+ exception_state(exception_state) {}
+ };
+
+ CallbackData callback_data(isolate, result, exception_state);
+ v8::Array::IterationCallback callback = [](uint32_t index,
+ v8::Local<v8::Value> v8_element,
+ void* data) {
+ CallbackData* callback_data = reinterpret_cast<CallbackData*>(data);
+ // 3.4. Initialize Si to the result of converting nextItem to an IDL value
+ // of type T.
+ v8::TypecheckWitness& witness = callback_data->witness;
+ // We can speed up type check by taking advantage of V8's type witness,
+ // provided traits' NativeValue implementation doesn't have additional
+ // logic beyond checking the type and calling ToScriptWrappable().
+ if constexpr (
+ NativeValueTraits<
+ T>::supports_scriptwrappable_specific_fast_array_iteration) {
+ if (witness.Matches(v8_element)) {
+ auto&& value = ToScriptWrappable(v8_element.As<v8::Object>())
+ ->template ToImpl<T>();
+ callback_data->result.push_back(std::move(value));
+ return v8::Array::CallbackResult::kContinue;
+ }
+ }
+ auto&& element = NativeValueTraits<T>::NativeValue(
+ callback_data->isolate, v8_element, callback_data->exception_state);
+ if (callback_data->exception_state.HadException()) {
+ // It doesn't matter whether we return `kException` or `kBreak` here,
+ // as that only affects the return value of `v8_array->Iterate()`,
+ // which we are ignoring.
+ return v8::Array::CallbackResult::kException;
+ }
+ if constexpr (
+ NativeValueTraits<
+ T>::supports_scriptwrappable_specific_fast_array_iteration) {
+ witness.Update(v8_element);
+ }
+ callback_data->result.push_back(std::move(element));
+ return v8::Array::CallbackResult::kContinue;
+ };
+ if (!v8_array->Iterate(current_context, callback, &callback_data)
+ .IsJust()) {
+ if (try_block.HasCaught()) {
+ exception_state.RethrowV8Exception(try_block.Exception());
+ }
+ DCHECK(exception_state.HadException());
+ return {};
+ }
+ return result;
+ }
+
// Array length may change if array is mutated during iteration.
for (uint32_t i = 0; i < v8_array->Length(); ++i) {
v8::Local<v8::Value> v8_element;
@@ -1056,6 +1132,7 @@ CreateIDLSequenceFromV8ArraySlow(v8::Isolate* isolate,
return {};
result.push_back(std::move(element));
}
+
// 3.2. If next is false, then return an IDL sequence value of type
// sequence<T> of length i, where the value of the element at index j is Sj.
return result;
@@ -1398,6 +1475,7 @@ struct NativeValueTraits<T> : public NativeValueTraitsBase<T*> {
}
};
+// Interface types
template <typename T>
requires std::derived_from<T, CallbackInterfaceBase>
struct NativeValueTraits<IDLNullable<T>>
@@ -1470,12 +1548,21 @@ struct NativeValueTraits<T> : public NativeValueTraitsBase<T> {
template <typename T>
requires std::derived_from<T, ScriptWrappable>
struct NativeValueTraits<T> : public NativeValueTraitsBase<T*> {
+ // This signifies that CreateIDLSequenceFromV8ArraySlow() may apply
+ // certain optimization based on assumptions about `NativeValue()`
+ // implementation below. For subclasses of ScriptWrappable that have
+ // different implementation of NativeValue(), this should remain false.
+ static constexpr bool supports_scriptwrappable_specific_fast_array_iteration =
+ true;
+
static inline T* NativeValue(v8::Isolate* isolate,
v8::Local<v8::Value> value,
ExceptionState& exception_state) {
const WrapperTypeInfo* wrapper_type_info = T::GetStaticWrapperTypeInfo();
- if (V8PerIsolateData::From(isolate)->HasInstance(wrapper_type_info, value))
+ if (V8PerIsolateData::From(isolate)->HasInstance(wrapper_type_info,
+ value)) {
return ToScriptWrappable(value.As<v8::Object>())->template ToImpl<T>();
+ }
bindings::NativeValueTraitsInterfaceNotOfType(wrapper_type_info,
exception_state);