d76064df4f
Previously, GCInfoTrait relied on the non-trivial constructor of a static object for registering a new GCInfo object. The generated code is required to be thread-safe which is achieved by introducing guard variables in the compiler. The new version is similar to Blink in that it relies on zero initialization of a trivially constructible atomic. Compared to guard variables that are created per GCInfo registration, the atomic creates less bloat (~20bytes/type) and also results in a better fast path. Minimum example: https://godbolt.org/z/qrdTf8 Bug: chromium:1056170 Change-Id: I95efbbf035b655d0440c9477f5391e310e2b71fa Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2764750 Reviewed-by: Omer Katz <omerkatz@chromium.org> Commit-Queue: Michael Lippautz <mlippautz@chromium.org> Cr-Commit-Position: refs/heads/master@{#73463}
76 lines
3.0 KiB
C++
76 lines
3.0 KiB
C++
// Copyright 2020 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef INCLUDE_CPPGC_INTERNAL_GC_INFO_H_
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#define INCLUDE_CPPGC_INTERNAL_GC_INFO_H_
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#include <atomic>
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#include <cstdint>
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#include "cppgc/internal/finalizer-trait.h"
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#include "cppgc/internal/name-trait.h"
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#include "cppgc/trace-trait.h"
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#include "v8config.h" // NOLINT(build/include_directory)
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namespace cppgc {
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namespace internal {
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using GCInfoIndex = uint16_t;
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// Acquires a new GC info object and returns the index. In addition, also
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// updates `registered_index` atomically.
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V8_EXPORT GCInfoIndex
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EnsureGCInfoIndex(std::atomic<GCInfoIndex>& registered_index,
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FinalizationCallback, TraceCallback, NameCallback, bool);
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// Fold types based on finalizer behavior. Note that finalizer characteristics
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// align with trace behavior, i.e., destructors are virtual when trace methods
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// are and vice versa.
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template <typename T, typename ParentMostGarbageCollectedType>
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struct GCInfoFolding {
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static constexpr bool kHasVirtualDestructorAtBase =
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std::has_virtual_destructor<ParentMostGarbageCollectedType>::value;
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static constexpr bool kBothTypesAreTriviallyDestructible =
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std::is_trivially_destructible<ParentMostGarbageCollectedType>::value &&
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std::is_trivially_destructible<T>::value;
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static constexpr bool kHasCustomFinalizerDispatchAtBase =
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internal::HasFinalizeGarbageCollectedObject<
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ParentMostGarbageCollectedType>::value;
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#ifdef CPPGC_SUPPORTS_OBJECT_NAMES
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static constexpr bool kWantsDetailedObjectNames = true;
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#else // !CPPGC_SUPPORTS_OBJECT_NAMES
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static constexpr bool kWantsDetailedObjectNames = false;
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#endif // !CPPGC_SUPPORTS_OBJECT_NAMES
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// Folding would regresses name resolution when deriving names from C++
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// class names as it would just folds a name to the base class name.
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using ResultType = std::conditional_t<(kHasVirtualDestructorAtBase ||
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kBothTypesAreTriviallyDestructible ||
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kHasCustomFinalizerDispatchAtBase) &&
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!kWantsDetailedObjectNames,
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ParentMostGarbageCollectedType, T>;
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};
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// Trait determines how the garbage collector treats objects wrt. to traversing,
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// finalization, and naming.
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template <typename T>
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struct GCInfoTrait final {
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static GCInfoIndex Index() {
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static_assert(sizeof(T), "T must be fully defined");
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static std::atomic<GCInfoIndex>
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registered_index; // Uses zero initialization.
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const GCInfoIndex index = registered_index.load(std::memory_order_acquire);
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return index ? index
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: EnsureGCInfoIndex(
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registered_index, FinalizerTrait<T>::kCallback,
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TraceTrait<T>::Trace, NameTrait<T>::GetName,
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std::is_polymorphic<T>::value);
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}
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};
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} // namespace internal
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} // namespace cppgc
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#endif // INCLUDE_CPPGC_INTERNAL_GC_INFO_H_
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