src/objects/backing-store.h - v8/v8.git - Git at Google

 // Copyright 2019 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 V8_OBJECTS_BACKING_STORE_H_
 #define V8_OBJECTS_BACKING_STORE_H_

 #include <memory>

 #include "include/v8-array-buffer.h"
 #include "include/v8-internal.h"
 #include "src/base/optional.h"
 #include "src/handles/handles.h"

 namespace v8 {
 namespace internal {

 class Isolate;
 class WasmMemoryObject;

 // Whether this is Wasm memory, and if 32 or 64 bit.
 enum class WasmMemoryFlag : uint8_t { kNotWasm, kWasmMemory32, kWasmMemory64 };

 // Whether the backing store is shared or not.
 enum class SharedFlag : uint8_t { kNotShared, kShared };

 // Whether the backing store is resizable or not.
 enum class ResizableFlag : uint8_t { kNotResizable, kResizable };

 // Whether the backing store memory is initialied to zero or not.
 enum class InitializedFlag : uint8_t { kUninitialized, kZeroInitialized };

 // Internal information for shared wasm memories. E.g. contains
 // a list of all memory objects (across all isolates) that share this
 // backing store.
 struct SharedWasmMemoryData;

 // The {BackingStore} data structure stores all the low-level details about the
 // backing store of an array buffer or Wasm memory, including its base address
 // and length, whether it is shared, provided by the embedder, has guard
 // regions, etc. Instances of this classes *own* the underlying memory
 // when they are created through one of the {Allocate()} methods below,
 // and the destructor frees the memory (and page allocation if necessary).
 class V8_EXPORT_PRIVATE BackingStore : public BackingStoreBase {
  public:
   ~BackingStore();

   // Allocate an array buffer backing store using the default method,
   // which currently is the embedder-provided array buffer allocator.
   static std::unique_ptr<BackingStore> Allocate(Isolate* isolate,
                                                 size_t byte_length,
                                                 SharedFlag shared,
                                                 InitializedFlag initialized);

 #if V8_ENABLE_WEBASSEMBLY
   // Allocate the backing store for a Wasm memory.
   static std::unique_ptr<BackingStore> AllocateWasmMemory(
       Isolate* isolate, size_t initial_pages, size_t maximum_pages,
       WasmMemoryFlag wasm_memory, SharedFlag shared);
 #endif  // V8_ENABLE_WEBASSEMBLY

   // Tries to allocate `maximum_pages` of memory and commit `initial_pages`.
   //
   // If {isolate} is not null, initial failure to allocate the backing store may
   // trigger GC, after which the allocation is retried. If {isolate} is null, no
   // GC will be triggered.
   static std::unique_ptr<BackingStore> TryAllocateAndPartiallyCommitMemory(
       Isolate* isolate, size_t byte_length, size_t max_byte_length,
       size_t page_size, size_t initial_pages, size_t maximum_pages,
       WasmMemoryFlag wasm_memory, SharedFlag shared);

   // Create a backing store that wraps existing allocated memory.
   static std::unique_ptr<BackingStore> WrapAllocation(
       void* allocation_base, size_t allocation_length,
       v8::BackingStore::DeleterCallback deleter, void* deleter_data,
       SharedFlag shared);

   // Create an empty backing store.
   static std::unique_ptr<BackingStore> EmptyBackingStore(SharedFlag shared);

   // Accessors.
   void* buffer_start() const { return buffer_start_; }
   size_t byte_length(
       std::memory_order memory_order = std::memory_order_relaxed) const {
     return byte_length_.load(memory_order);
   }
   size_t max_byte_length() const { return max_byte_length_; }
   size_t byte_capacity() const { return byte_capacity_; }
   bool is_shared() const { return is_shared_; }
   bool is_resizable_by_js() const { return is_resizable_by_js_; }
   bool is_wasm_memory() const { return is_wasm_memory_; }
   bool has_guard_regions() const { return has_guard_regions_; }

   bool IsEmpty() const {
     DCHECK_GE(byte_capacity_, byte_length_);
     return byte_capacity_ == 0;
   }

   enum ResizeOrGrowResult { kSuccess, kFailure, kRace };

   ResizeOrGrowResult ResizeInPlace(Isolate* isolate, size_t new_byte_length);
   ResizeOrGrowResult GrowInPlace(Isolate* isolate, size_t new_byte_length);

   bool CanReallocate() const {
     return !is_wasm_memory_ && !custom_deleter_ && !globally_registered_ &&
            !is_resizable_by_js_ && buffer_start_ != nullptr;
   }

   // Wrapper around ArrayBuffer::Allocator::Reallocate.
   bool Reallocate(Isolate* isolate, size_t new_byte_length);

 #if V8_ENABLE_WEBASSEMBLY
   // Attempt to grow this backing store in place.
   base::Optional<size_t> GrowWasmMemoryInPlace(Isolate* isolate,
                                                size_t delta_pages,
                                                size_t max_pages);

   // Allocate a new, larger, backing store for this Wasm memory and copy the
   // contents of this backing store into it.
   std::unique_ptr<BackingStore> CopyWasmMemory(Isolate* isolate,
                                                size_t new_pages,
                                                size_t max_pages,
                                                WasmMemoryFlag wasm_memory);

   // Attach the given memory object to this backing store. The memory object
   // will be updated if this backing store is grown.
   void AttachSharedWasmMemoryObject(Isolate* isolate,
                                     Handle<WasmMemoryObject> memory_object);

   // Send asynchronous updates to attached memory objects in other isolates
   // after the backing store has been grown. Memory objects in this
   // isolate are updated synchronously.
   void BroadcastSharedWasmMemoryGrow(Isolate* isolate) const;

   // Remove all memory objects in the given isolate that refer to this
   // backing store.
   static void RemoveSharedWasmMemoryObjects(Isolate* isolate);

   // Update all shared memory objects in this isolate (after a grow operation).
   static void UpdateSharedWasmMemoryObjects(Isolate* isolate);
 #endif  // V8_ENABLE_WEBASSEMBLY

   // Returns the size of the external memory owned by this backing store.
   // It is used for triggering GCs based on the external memory pressure.
   size_t PerIsolateAccountingLength() {
     if (is_shared_) {
       // TODO(titzer): SharedArrayBuffers and shared WasmMemorys cause problems
       // with accounting for per-isolate external memory. In particular, sharing
       // the same array buffer or memory multiple times, which happens in stress
       // tests, can cause overcounting, leading to GC thrashing. Fix with global
       // accounting?
       return 0;
     }
     if (empty_deleter_) {
       // The backing store has an empty deleter. Even if the backing store is
       // freed after GC, it would not free the memory block.
       return 0;
     }
     return byte_length();
   }

   uint32_t id() const { return id_; }

  private:
   friend class GlobalBackingStoreRegistry;

   BackingStore(void* buffer_start, size_t byte_length, size_t max_byte_length,
                size_t byte_capacity, SharedFlag shared, ResizableFlag resizable,
                bool is_wasm_memory, bool is_wasm_memory64,
                bool has_guard_regions, bool custom_deleter, bool empty_deleter);
   BackingStore(const BackingStore&) = delete;
   BackingStore& operator=(const BackingStore&) = delete;
   void SetAllocatorFromIsolate(Isolate* isolate);

   // Accessors for type-specific data.
   v8::ArrayBuffer::Allocator* get_v8_api_array_buffer_allocator();
   SharedWasmMemoryData* get_shared_wasm_memory_data() const;

   void* buffer_start_ = nullptr;
   std::atomic<size_t> byte_length_;
   // Max byte length of the corresponding JSArrayBuffer(s).
   size_t max_byte_length_;
   // Amount of the memory allocated
   size_t byte_capacity_;
   // Unique ID of this backing store. Currently only used by DevTools, to
   // identify stores used by several ArrayBuffers or WebAssembly memories
   // (reported by the inspector as [[ArrayBufferData]] internal property)
   const uint32_t id_;

   union TypeSpecificData {
     TypeSpecificData() : v8_api_array_buffer_allocator(nullptr) {}
     ~TypeSpecificData() {}

     // If this backing store was allocated through the ArrayBufferAllocator API,
     // this is a direct pointer to the API object for freeing the backing
     // store.
     v8::ArrayBuffer::Allocator* v8_api_array_buffer_allocator;

     // Holds a shared_ptr to the ArrayBuffer::Allocator instance, if requested
     // so by the embedder through setting
     // Isolate::CreateParams::array_buffer_allocator_shared.
     std::shared_ptr<v8::ArrayBuffer::Allocator>
         v8_api_array_buffer_allocator_shared;

     // For shared Wasm memories, this is a list of all the attached memory
     // objects, which is needed to grow shared backing stores.
     SharedWasmMemoryData* shared_wasm_memory_data;

     // Custom deleter for the backing stores that wrap memory blocks that are
     // allocated with a custom allocator.
     struct DeleterInfo {
       v8::BackingStore::DeleterCallback callback;
       void* data;
     } deleter;
   } type_specific_data_;

   const bool is_shared_ : 1;
   // Backing stores for (Resizable|GrowableShared)ArrayBuffer
   const bool is_resizable_by_js_ : 1;
   const bool is_wasm_memory_ : 1;
   const bool is_wasm_memory64_ : 1;
   bool holds_shared_ptr_to_allocator_ : 1;
   const bool has_guard_regions_ : 1;
   bool globally_registered_ : 1;
   const bool custom_deleter_ : 1;
   const bool empty_deleter_ : 1;
 };

 // A global, per-process mapping from buffer addresses to backing stores
 // of wasm memory objects.
 class GlobalBackingStoreRegistry {
  public:
   // Register a backing store in the global registry. A mapping from the
   // {buffer_start} to the backing store object will be added. The backing
   // store will automatically unregister itself upon destruction.
   // Only wasm memory backing stores are supported.
   static void Register(std::shared_ptr<BackingStore> backing_store);

  private:
   friend class BackingStore;
   // Unregister a backing store in the global registry.
   static void Unregister(BackingStore* backing_store);

   // Adds the given memory object to the backing store's weak list
   // of memory objects (under the registry lock).
   static void AddSharedWasmMemoryObject(Isolate* isolate,
                                         BackingStore* backing_store,
                                         Handle<WasmMemoryObject> memory_object);

   // Purge any shared wasm memory lists that refer to this isolate.
   static void Purge(Isolate* isolate);

   // Broadcast updates to all attached memory objects.
   static void BroadcastSharedWasmMemoryGrow(Isolate* isolate,
                                             const BackingStore* backing_store);

   // Update all shared memory objects in the given isolate.
   static void UpdateSharedWasmMemoryObjects(Isolate* isolate);
 };

 }  // namespace internal
 }  // namespace v8

 #endif  // V8_OBJECTS_BACKING_STORE_H_
	// Copyright 2019 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 V8_OBJECTS_BACKING_STORE_H_
	#define V8_OBJECTS_BACKING_STORE_H_

	#include <memory>

	#include "include/v8-array-buffer.h"
	#include "include/v8-internal.h"
	#include "src/base/optional.h"
	#include "src/handles/handles.h"

	namespace v8 {
	namespace internal {

	class Isolate;
	class WasmMemoryObject;

	// Whether this is Wasm memory, and if 32 or 64 bit.
	enum class WasmMemoryFlag : uint8_t { kNotWasm, kWasmMemory32, kWasmMemory64 };

	// Whether the backing store is shared or not.
	enum class SharedFlag : uint8_t { kNotShared, kShared };

	// Whether the backing store is resizable or not.
	enum class ResizableFlag : uint8_t { kNotResizable, kResizable };

	// Whether the backing store memory is initialied to zero or not.
	enum class InitializedFlag : uint8_t { kUninitialized, kZeroInitialized };

	// Internal information for shared wasm memories. E.g. contains
	// a list of all memory objects (across all isolates) that share this
	// backing store.
	struct SharedWasmMemoryData;

	// The {BackingStore} data structure stores all the low-level details about the
	// backing store of an array buffer or Wasm memory, including its base address
	// and length, whether it is shared, provided by the embedder, has guard
	// regions, etc. Instances of this classes own the underlying memory
	// when they are created through one of the {Allocate()} methods below,
	// and the destructor frees the memory (and page allocation if necessary).
	class V8_EXPORT_PRIVATE BackingStore : public BackingStoreBase {
	public:
	~BackingStore();

	// Allocate an array buffer backing store using the default method,
	// which currently is the embedder-provided array buffer allocator.
	static std::unique_ptr<BackingStore> Allocate(Isolate* isolate,
	size_t byte_length,
	SharedFlag shared,
	InitializedFlag initialized);

	#if V8_ENABLE_WEBASSEMBLY
	// Allocate the backing store for a Wasm memory.
	static std::unique_ptr<BackingStore> AllocateWasmMemory(
	Isolate* isolate, size_t initial_pages, size_t maximum_pages,
	WasmMemoryFlag wasm_memory, SharedFlag shared);
	#endif // V8_ENABLE_WEBASSEMBLY

	// Tries to allocate `maximum_pages` of memory and commit `initial_pages`.
	//
	// If {isolate} is not null, initial failure to allocate the backing store may
	// trigger GC, after which the allocation is retried. If {isolate} is null, no
	// GC will be triggered.
	static std::unique_ptr<BackingStore> TryAllocateAndPartiallyCommitMemory(
	Isolate* isolate, size_t byte_length, size_t max_byte_length,
	size_t page_size, size_t initial_pages, size_t maximum_pages,
	WasmMemoryFlag wasm_memory, SharedFlag shared);

	// Create a backing store that wraps existing allocated memory.
	static std::unique_ptr<BackingStore> WrapAllocation(
	void* allocation_base, size_t allocation_length,
	v8::BackingStore::DeleterCallback deleter, void* deleter_data,
	SharedFlag shared);

	// Create an empty backing store.
	static std::unique_ptr<BackingStore> EmptyBackingStore(SharedFlag shared);

	// Accessors.
	void* buffer_start() const { return buffer_start_; }
	size_t byte_length(
	std::memory_order memory_order = std::memory_order_relaxed) const {
	return byte_length_.load(memory_order);
	}
	size_t max_byte_length() const { return max_byte_length_; }
	size_t byte_capacity() const { return byte_capacity_; }
	bool is_shared() const { return is_shared_; }
	bool is_resizable_by_js() const { return is_resizable_by_js_; }
	bool is_wasm_memory() const { return is_wasm_memory_; }
	bool has_guard_regions() const { return has_guard_regions_; }

	bool IsEmpty() const {
	DCHECK_GE(byte_capacity_, byte_length_);
	return byte_capacity_ == 0;
	}

	enum ResizeOrGrowResult { kSuccess, kFailure, kRace };

	ResizeOrGrowResult ResizeInPlace(Isolate* isolate, size_t new_byte_length);
	ResizeOrGrowResult GrowInPlace(Isolate* isolate, size_t new_byte_length);

	bool CanReallocate() const {
	return !is_wasm_memory_ && !custom_deleter_ && !globally_registered_ &&
	!is_resizable_by_js_ && buffer_start_ != nullptr;
	}

	// Wrapper around ArrayBuffer::Allocator::Reallocate.
	bool Reallocate(Isolate* isolate, size_t new_byte_length);

	#if V8_ENABLE_WEBASSEMBLY
	// Attempt to grow this backing store in place.
	base::Optional<size_t> GrowWasmMemoryInPlace(Isolate* isolate,
	size_t delta_pages,
	size_t max_pages);

	// Allocate a new, larger, backing store for this Wasm memory and copy the
	// contents of this backing store into it.
	std::unique_ptr<BackingStore> CopyWasmMemory(Isolate* isolate,
	size_t new_pages,
	size_t max_pages,
	WasmMemoryFlag wasm_memory);

	// Attach the given memory object to this backing store. The memory object
	// will be updated if this backing store is grown.
	void AttachSharedWasmMemoryObject(Isolate* isolate,
	Handle<WasmMemoryObject> memory_object);

	// Send asynchronous updates to attached memory objects in other isolates
	// after the backing store has been grown. Memory objects in this
	// isolate are updated synchronously.
	void BroadcastSharedWasmMemoryGrow(Isolate* isolate) const;

	// Remove all memory objects in the given isolate that refer to this
	// backing store.
	static void RemoveSharedWasmMemoryObjects(Isolate* isolate);

	// Update all shared memory objects in this isolate (after a grow operation).
	static void UpdateSharedWasmMemoryObjects(Isolate* isolate);
	#endif // V8_ENABLE_WEBASSEMBLY

	// Returns the size of the external memory owned by this backing store.
	// It is used for triggering GCs based on the external memory pressure.
	size_t PerIsolateAccountingLength() {
	if (is_shared_) {
	// TODO(titzer): SharedArrayBuffers and shared WasmMemorys cause problems
	// with accounting for per-isolate external memory. In particular, sharing
	// the same array buffer or memory multiple times, which happens in stress
	// tests, can cause overcounting, leading to GC thrashing. Fix with global
	// accounting?
	return 0;
	}
	if (empty_deleter_) {
	// The backing store has an empty deleter. Even if the backing store is
	// freed after GC, it would not free the memory block.
	return 0;
	}
	return byte_length();
	}

	uint32_t id() const { return id_; }

	private:
	friend class GlobalBackingStoreRegistry;

	BackingStore(void* buffer_start, size_t byte_length, size_t max_byte_length,
	size_t byte_capacity, SharedFlag shared, ResizableFlag resizable,
	bool is_wasm_memory, bool is_wasm_memory64,
	bool has_guard_regions, bool custom_deleter, bool empty_deleter);
	BackingStore(const BackingStore&) = delete;
	BackingStore& operator=(const BackingStore&) = delete;
	void SetAllocatorFromIsolate(Isolate* isolate);

	// Accessors for type-specific data.
	v8::ArrayBuffer::Allocator* get_v8_api_array_buffer_allocator();
	SharedWasmMemoryData* get_shared_wasm_memory_data() const;

	void* buffer_start_ = nullptr;
	std::atomic<size_t> byte_length_;
	// Max byte length of the corresponding JSArrayBuffer(s).
	size_t max_byte_length_;
	// Amount of the memory allocated
	size_t byte_capacity_;
	// Unique ID of this backing store. Currently only used by DevTools, to
	// identify stores used by several ArrayBuffers or WebAssembly memories
	// (reported by the inspector as [[ArrayBufferData]] internal property)
	const uint32_t id_;

	union TypeSpecificData {
	TypeSpecificData() : v8_api_array_buffer_allocator(nullptr) {}
	~TypeSpecificData() {}

	// If this backing store was allocated through the ArrayBufferAllocator API,
	// this is a direct pointer to the API object for freeing the backing
	// store.
	v8::ArrayBuffer::Allocator* v8_api_array_buffer_allocator;

	// Holds a shared_ptr to the ArrayBuffer::Allocator instance, if requested
	// so by the embedder through setting
	// Isolate::CreateParams::array_buffer_allocator_shared.
	std::shared_ptr<v8::ArrayBuffer::Allocator>
	v8_api_array_buffer_allocator_shared;

	// For shared Wasm memories, this is a list of all the attached memory
	// objects, which is needed to grow shared backing stores.
	SharedWasmMemoryData* shared_wasm_memory_data;

	// Custom deleter for the backing stores that wrap memory blocks that are
	// allocated with a custom allocator.
	struct DeleterInfo {
	v8::BackingStore::DeleterCallback callback;
	void* data;
	} deleter;
	} type_specific_data_;

	const bool is_shared_ : 1;
	// Backing stores for (Resizable\|GrowableShared)ArrayBuffer
	const bool is_resizable_by_js_ : 1;
	const bool is_wasm_memory_ : 1;
	const bool is_wasm_memory64_ : 1;
	bool holds_shared_ptr_to_allocator_ : 1;
	const bool has_guard_regions_ : 1;
	bool globally_registered_ : 1;
	const bool custom_deleter_ : 1;
	const bool empty_deleter_ : 1;
	};

	// A global, per-process mapping from buffer addresses to backing stores
	// of wasm memory objects.
	class GlobalBackingStoreRegistry {
	public:
	// Register a backing store in the global registry. A mapping from the
	// {buffer_start} to the backing store object will be added. The backing
	// store will automatically unregister itself upon destruction.
	// Only wasm memory backing stores are supported.
	static void Register(std::shared_ptr<BackingStore> backing_store);

	private:
	friend class BackingStore;
	// Unregister a backing store in the global registry.
	static void Unregister(BackingStore* backing_store);

	// Adds the given memory object to the backing store's weak list
	// of memory objects (under the registry lock).
	static void AddSharedWasmMemoryObject(Isolate* isolate,
	BackingStore* backing_store,
	Handle<WasmMemoryObject> memory_object);

	// Purge any shared wasm memory lists that refer to this isolate.
	static void Purge(Isolate* isolate);

	// Broadcast updates to all attached memory objects.
	static void BroadcastSharedWasmMemoryGrow(Isolate* isolate,
	const BackingStore* backing_store);

	// Update all shared memory objects in the given isolate.
	static void UpdateSharedWasmMemoryObjects(Isolate* isolate);
	};

	} // namespace internal
	} // namespace v8

	#endif // V8_OBJECTS_BACKING_STORE_H_