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3a2f2f3926
Per spec, every `await` goes through PromiseResolve (which wraps the value in a new Promise via NewPromiseCapability) and then PerformPromiseThen (which creates PromiseReaction and JobCallback objects). This results in 13-16 GC cell allocations per await. Add a fast path that detects two common cases: 1. Primitive values: These can never have a "then" property, so we can skip all promise wrapping and directly schedule the async function's continuation as a microtask. 2. Already-settled native Promises: If the promise has no own properties and its prototype is the intrinsic %Promise.prototype%, we can extract the result directly and schedule continuation. For these cases, we bypass promise_resolve(), new_promise_capability(), create_resolving_functions(), perform_then(), PromiseReaction creation, and JobCallback creation -- replacing ~13 GC allocations with 1 (the GC::Function for the microtask job).
42 lines
1.2 KiB
C++
42 lines
1.2 KiB
C++
/*
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* Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <LibJS/Bytecode/Interpreter.h>
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#include <LibJS/Runtime/ECMAScriptFunctionObject.h>
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#include <LibJS/Runtime/GeneratorObject.h>
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#include <LibJS/Runtime/Object.h>
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#include <LibJS/Runtime/Promise.h>
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namespace JS {
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class AsyncFunctionDriverWrapper final : public Promise {
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JS_OBJECT(AsyncFunctionDriverWrapper, Promise);
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GC_DECLARE_ALLOCATOR(AsyncFunctionDriverWrapper);
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public:
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[[nodiscard]] static GC::Ref<Promise> create(Realm&, GeneratorObject*);
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virtual ~AsyncFunctionDriverWrapper() override = default;
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void visit_edges(Cell::Visitor&) override;
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void continue_async_execution(VM&, Value, bool is_successful);
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void schedule_resume(Value, bool is_fulfilled);
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private:
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AsyncFunctionDriverWrapper(Realm&, GC::Ref<GeneratorObject>, GC::Ref<Promise> top_level_promise);
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ThrowCompletionOr<void> await(Value);
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GC::Ref<GeneratorObject> m_generator_object;
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GC::Ref<Promise> m_top_level_promise;
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GC::Ptr<Promise> m_current_promise { nullptr };
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OwnPtr<ExecutionContext> m_suspended_execution_context;
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GC::Ptr<NativeFunction> m_on_settled;
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};
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}
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