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// Copyright 2016 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_HEAP_EMBEDDER_TRACING_H_
#define V8_HEAP_EMBEDDER_TRACING_H_
#include "include/v8-cppgc.h"
#include "include/v8.h"
#include "src/common/globals.h"
#include "src/flags/flags.h"
namespace v8 {
namespace internal {
class Heap;
class JSObject;
class V8_EXPORT_PRIVATE DefaultEmbedderRootsHandler final
: public EmbedderRootsHandler {
public:
bool IsRoot(const v8::TracedReference<v8::Value>& handle) final;
bool IsRoot(const v8::TracedGlobal<v8::Value>& handle) final;
void ResetRoot(const v8::TracedReference<v8::Value>& handle) final;
void SetTracer(EmbedderHeapTracer* tracer) { tracer_ = tracer; }
private:
EmbedderHeapTracer* tracer_ = nullptr;
};
class V8_EXPORT_PRIVATE LocalEmbedderHeapTracer final {
public:
using WrapperInfo = std::pair<void*, void*>;
using WrapperCache = std::vector<WrapperInfo>;
// WrapperInfo is passed over the API. Use VerboseWrapperInfo to access pair
// internals in a named way. See ProcessingScope::TracePossibleJSWrapper()
// below on how a V8 object is parsed to gather the information.
struct VerboseWrapperInfo {
constexpr explicit VerboseWrapperInfo(const WrapperInfo& raw_info)
: raw_info(raw_info) {}
// Information describing the type pointed to via instance().
void* type_info() const { return raw_info.first; }
// Direct pointer to an instance described by type_info().
void* instance() const { return raw_info.second; }
// Returns whether the info is empty and thus does not keep a C++ object
// alive.
bool is_empty() const { return !type_info() || !instance(); }
const WrapperInfo& raw_info;
};
class V8_EXPORT_PRIVATE V8_NODISCARD ProcessingScope {
public:
explicit ProcessingScope(LocalEmbedderHeapTracer* tracer);
~ProcessingScope();
void TracePossibleWrapper(JSObject js_object);
void AddWrapperInfoForTesting(WrapperInfo info);
private:
static constexpr size_t kWrapperCacheSize = 1000;
void FlushWrapperCacheIfFull();
LocalEmbedderHeapTracer* const tracer_;
const WrapperDescriptor wrapper_descriptor_;
WrapperCache wrapper_cache_;
};
explicit LocalEmbedderHeapTracer(Isolate* isolate) : isolate_(isolate) {}
~LocalEmbedderHeapTracer() {
if (remote_tracer_) remote_tracer_->isolate_ = nullptr;
}
bool InUse() const { return remote_tracer_ != nullptr; }
EmbedderHeapTracer* remote_tracer() const { return remote_tracer_; }
void SetRemoteTracer(EmbedderHeapTracer* tracer);
void TracePrologue(EmbedderHeapTracer::TraceFlags flags);
void TraceEpilogue();
void EnterFinalPause();
bool Trace(double deadline);
bool IsRemoteTracingDone();
bool ShouldFinalizeIncrementalMarking() {
return !FLAG_incremental_marking_wrappers || !InUse() ||
(IsRemoteTracingDone() && embedder_worklist_empty_);
}
void SetEmbedderStackStateForNextFinalization(
EmbedderHeapTracer::EmbedderStackState stack_state);
void SetEmbedderWorklistEmpty(bool is_empty) {
embedder_worklist_empty_ = is_empty;
}
void IncreaseAllocatedSize(size_t bytes) {
remote_stats_.used_size += bytes;
remote_stats_.allocated_size += bytes;
if (remote_stats_.allocated_size >
remote_stats_.allocated_size_limit_for_check) {
StartIncrementalMarkingIfNeeded();
remote_stats_.allocated_size_limit_for_check =
remote_stats_.allocated_size + kEmbedderAllocatedThreshold;
}
}
void DecreaseAllocatedSize(size_t bytes) {
DCHECK_GE(remote_stats_.used_size, bytes);
remote_stats_.used_size -= bytes;
}
void StartIncrementalMarkingIfNeeded();
size_t used_size() const { return remote_stats_.used_size; }
size_t allocated_size() const { return remote_stats_.allocated_size; }
WrapperInfo ExtractWrapperInfo(Isolate* isolate, JSObject js_object);
void SetWrapperDescriptor(const WrapperDescriptor& wrapper_descriptor) {
wrapper_descriptor_ = wrapper_descriptor;
}
void UpdateRemoteStats(size_t, double);
DefaultEmbedderRootsHandler& default_embedder_roots_handler() {
return default_embedder_roots_handler_;
}
void NotifyEmptyEmbedderStack();
private:
static constexpr size_t kEmbedderAllocatedThreshold = 128 * KB;
static constexpr WrapperDescriptor::InternalFieldIndex
kDefaultWrapperTypeEmbedderIndex = 0;
static constexpr WrapperDescriptor::InternalFieldIndex
kDefaultWrapperInstanceEmbedderIndex = 1;
static constexpr WrapperDescriptor GetDefaultWrapperDescriptor() {
// The default descriptor assumes the indices that known embedders use.
return WrapperDescriptor(kDefaultWrapperTypeEmbedderIndex,
kDefaultWrapperInstanceEmbedderIndex,
WrapperDescriptor::kUnknownEmbedderId);
}
Isolate* const isolate_;
EmbedderHeapTracer* remote_tracer_ = nullptr;
DefaultEmbedderRootsHandler default_embedder_roots_handler_;
EmbedderHeapTracer::EmbedderStackState embedder_stack_state_ =
EmbedderHeapTracer::EmbedderStackState::kMayContainHeapPointers;
// Indicates whether the embedder worklist was observed empty on the main
// thread. This is opportunistic as concurrent marking tasks may hold local
// segments of potential embedder fields to move to the main thread.
bool embedder_worklist_empty_ = false;
struct RemoteStatistics {
// Used size of objects in bytes reported by the embedder. Updated via
// TraceSummary at the end of tracing and incrementally when the GC is not
// in progress.
size_t used_size = 0;
// Totally bytes allocated by the embedder. Monotonically
// increasing value. Used to approximate allocation rate.
size_t allocated_size = 0;
// Limit for |allocated_size| in bytes to avoid checking for starting a GC
// on each increment.
size_t allocated_size_limit_for_check = 0;
} remote_stats_;
// Default descriptor only used when the embedder is using EmbedderHeapTracer.
// The value is overriden by CppHeap with values that the embedder provided
// upon initialization.
WrapperDescriptor wrapper_descriptor_ = GetDefaultWrapperDescriptor();
friend class EmbedderStackStateScope;
};
class V8_EXPORT_PRIVATE V8_NODISCARD EmbedderStackStateScope final {
public:
EmbedderStackStateScope(LocalEmbedderHeapTracer* local_tracer,
EmbedderHeapTracer::EmbedderStackState stack_state)
: local_tracer_(local_tracer),
old_stack_state_(local_tracer_->embedder_stack_state_) {
local_tracer_->embedder_stack_state_ = stack_state;
if (EmbedderHeapTracer::EmbedderStackState::kNoHeapPointers == stack_state)
local_tracer_->NotifyEmptyEmbedderStack();
}
~EmbedderStackStateScope() {
local_tracer_->embedder_stack_state_ = old_stack_state_;
}
private:
LocalEmbedderHeapTracer* const local_tracer_;
const EmbedderHeapTracer::EmbedderStackState old_stack_state_;
};
} // namespace internal
} // namespace v8
#endif // V8_HEAP_EMBEDDER_TRACING_H_
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