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v8/include/v8-cppgc.h

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+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef INCLUDE_V8_CPPGC_H_
+#define INCLUDE_V8_CPPGC_H_
+
+#include <cstdint>
+#include <memory>
+#include <vector>
+
+#include "cppgc/common.h"
+#include "cppgc/custom-space.h"
+#include "cppgc/heap-statistics.h"
+#include "cppgc/visitor.h"
+#include "v8-internal.h"       // NOLINT(build/include_directory)
+#include "v8-platform.h"       // NOLINT(build/include_directory)
+#include "v8-traced-handle.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+class AllocationHandle;
+class HeapHandle;
+}  // namespace cppgc
+
+namespace v8 {
+
+class Object;
+
+namespace internal {
+class CppHeap;
+}  // namespace internal
+
+class CustomSpaceStatisticsReceiver;
+
+/**
+ * Describes how V8 wrapper objects maintain references to garbage-collected C++
+ * objects.
+ */
+struct WrapperDescriptor final {
+  /**
+   * The index used on `v8::Ojbect::SetAlignedPointerFromInternalField()` and
+   * related APIs to add additional data to an object which is used to identify
+   * JS->C++ references.
+   */
+  using InternalFieldIndex = int;
+
+  /**
+   * Unknown embedder id. The value is reserved for internal usages and must not
+   * be used with `CppHeap`.
+   */
+  static constexpr uint16_t kUnknownEmbedderId = UINT16_MAX;
+
+  constexpr WrapperDescriptor(InternalFieldIndex wrappable_type_index,
+                              InternalFieldIndex wrappable_instance_index,
+                              uint16_t embedder_id_for_garbage_collected)
+      : wrappable_type_index(wrappable_type_index),
+        wrappable_instance_index(wrappable_instance_index),
+        embedder_id_for_garbage_collected(embedder_id_for_garbage_collected) {}
+
+  /**
+   * Index of the wrappable type.
+   */
+  InternalFieldIndex wrappable_type_index;
+
+  /**
+   * Index of the wrappable instance.
+   */
+  InternalFieldIndex wrappable_instance_index;
+
+  /**
+   * Embedder id identifying instances of garbage-collected objects. It is
+   * expected that the first field of the wrappable type is a uint16_t holding
+   * the id. Only references to instances of wrappables types with an id of
+   * `embedder_id_for_garbage_collected` will be considered by CppHeap.
+   */
+  uint16_t embedder_id_for_garbage_collected;
+};
+
+struct V8_EXPORT CppHeapCreateParams {
+  std::vector<std::unique_ptr<cppgc::CustomSpaceBase>> custom_spaces;
+  WrapperDescriptor wrapper_descriptor;
+  /**
+   * Specifies which kind of marking are supported by the heap. The type may be
+   * further reduced via runtime flags when attaching the heap to an Isolate.
+   */
+  cppgc::Heap::MarkingType marking_support =
+      cppgc::Heap::MarkingType::kIncrementalAndConcurrent;
+  /**
+   * Specifies which kind of sweeping is supported by the heap. The type may be
+   * further reduced via runtime flags when attaching the heap to an Isolate.
+   */
+  cppgc::Heap::SweepingType sweeping_support =
+      cppgc::Heap::SweepingType::kIncrementalAndConcurrent;
+};
+
+/**
+ * A heap for allocating managed C++ objects.
+ */
+class V8_EXPORT CppHeap {
+ public:
+  static std::unique_ptr<CppHeap> Create(v8::Platform* platform,
+                                         const CppHeapCreateParams& params);
+
+  virtual ~CppHeap() = default;
+
+  /**
+   * \returns the opaque handle for allocating objects using
+   * `MakeGarbageCollected()`.
+   */
+  cppgc::AllocationHandle& GetAllocationHandle();
+
+  /**
+   * \returns the opaque heap handle which may be used to refer to this heap in
+   *   other APIs. Valid as long as the underlying `CppHeap` is alive.
+   */
+  cppgc::HeapHandle& GetHeapHandle();
+
+  /**
+   * Terminate clears all roots and performs multiple garbage collections to
+   * reclaim potentially newly created objects in destructors.
+   *
+   * After this call, object allocation is prohibited.
+   */
+  void Terminate();
+
+  /**
+   * \param detail_level specifies whether should return detailed
+   *   statistics or only brief summary statistics.
+   * \returns current CppHeap statistics regarding memory consumption
+   *   and utilization.
+   */
+  cppgc::HeapStatistics CollectStatistics(
+      cppgc::HeapStatistics::DetailLevel detail_level);
+
+  /**
+   * Collects statistics for the given spaces and reports them to the receiver.
+   *
+   * \param custom_spaces a collection of custom space indicies.
+   * \param receiver an object that gets the results.
+   */
+  void CollectCustomSpaceStatisticsAtLastGC(
+      std::vector<cppgc::CustomSpaceIndex> custom_spaces,
+      std::unique_ptr<CustomSpaceStatisticsReceiver> receiver);
+
+  /**
+   * Enables a detached mode that allows testing garbage collection using
+   * `cppgc::testing` APIs. Once used, the heap cannot be attached to an
+   * `Isolate` anymore.
+   */
+  void EnableDetachedGarbageCollectionsForTesting();
+
+  /**
+   * Performs a stop-the-world garbage collection for testing purposes.
+   *
+   * \param stack_state The stack state to assume for the garbage collection.
+   */
+  void CollectGarbageForTesting(cppgc::EmbedderStackState stack_state);
+
+  /**
+   * Performs a stop-the-world minor garbage collection for testing purposes.
+   *
+   * \param stack_state The stack state to assume for the garbage collection.
+   */
+  void CollectGarbageInYoungGenerationForTesting(
+      cppgc::EmbedderStackState stack_state);
+
+ private:
+  CppHeap() = default;
+
+  friend class internal::CppHeap;
+};
+
+class JSVisitor : public cppgc::Visitor {
+ public:
+  explicit JSVisitor(cppgc::Visitor::Key key) : cppgc::Visitor(key) {}
+  ~JSVisitor() override = default;
+
+  void Trace(const TracedReferenceBase& ref) {
+    if (ref.IsEmptyThreadSafe()) return;
+    Visit(ref);
+  }
+
+ protected:
+  using cppgc::Visitor::Visit;
+
+  virtual void Visit(const TracedReferenceBase& ref) {}
+};
+
+/**
+ * Provided as input to `CppHeap::CollectCustomSpaceStatisticsAtLastGC()`.
+ *
+ * Its method is invoked with the results of the statistic collection.
+ */
+class CustomSpaceStatisticsReceiver {
+ public:
+  virtual ~CustomSpaceStatisticsReceiver() = default;
+  /**
+   * Reports the size of a space at the last GC. It is called for each space
+   * that was requested in `CollectCustomSpaceStatisticsAtLastGC()`.
+   *
+   * \param space_index The index of the space.
+   * \param bytes The total size of live objects in the space at the last GC.
+   *    It is zero if there was no GC yet.
+   */
+  virtual void AllocatedBytes(cppgc::CustomSpaceIndex space_index,
+                              size_t bytes) = 0;
+};
+
+}  // namespace v8
+
+namespace cppgc {
+
+template <typename T>
+struct TraceTrait<v8::TracedReference<T>> {
+  static cppgc::TraceDescriptor GetTraceDescriptor(const void* self) {
+    return {nullptr, Trace};
+  }
+
+  static void Trace(Visitor* visitor, const void* self) {
+    static_cast<v8::JSVisitor*>(visitor)->Trace(
+        *static_cast<const v8::TracedReference<T>*>(self));
+  }
+};
+
+}  // namespace cppgc
+
+#endif  // INCLUDE_V8_CPPGC_H_