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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.
#include "src/heap/cppgc/write-barrier.h"
#include "include/cppgc/heap-consistency.h"
#include "include/cppgc/internal/pointer-policies.h"
#include "src/heap/cppgc/globals.h"
#include "src/heap/cppgc/heap-object-header.h"
#include "src/heap/cppgc/heap-page.h"
#include "src/heap/cppgc/heap.h"
#include "src/heap/cppgc/marker.h"
#include "src/heap/cppgc/marking-visitor.h"
#if defined(CPPGC_CAGED_HEAP)
#include "include/cppgc/internal/caged-heap-local-data.h"
#endif
namespace cppgc {
namespace internal {
// static
AtomicEntryFlag WriteBarrier::write_barrier_enabled_;
namespace {
template <MarkerBase::WriteBarrierType type>
void ProcessMarkValue(HeapObjectHeader& header, MarkerBase* marker,
const void* value) {
DCHECK(marker->heap().is_incremental_marking_in_progress());
DCHECK(header.IsMarked<AccessMode::kAtomic>());
DCHECK(marker);
if (V8_UNLIKELY(header.IsInConstruction<AccessMode::kNonAtomic>())) {
// In construction objects are traced only if they are unmarked. If marking
// reaches this object again when it is fully constructed, it will re-mark
// it and tracing it as a previously not fully constructed object would know
// to bail out.
header.Unmark<AccessMode::kAtomic>();
marker->WriteBarrierForInConstructionObject(header);
return;
}
marker->WriteBarrierForObject<type>(header);
}
} // namespace
// static
void WriteBarrier::DijkstraMarkingBarrierSlowWithSentinelCheck(
const void* value) {
if (!value || value == kSentinelPointer) return;
DijkstraMarkingBarrierSlow(value);
}
// static
void WriteBarrier::DijkstraMarkingBarrierSlow(const void* value) {
const BasePage* page = BasePage::FromPayload(value);
const auto& heap = page->heap();
// GetWriteBarrierType() checks marking state.
DCHECK(heap.marker());
// No write barriers should be executed from atomic pause marking.
DCHECK(!heap.in_atomic_pause());
auto& header =
const_cast<HeapObjectHeader&>(page->ObjectHeaderFromInnerAddress(value));
if (!header.TryMarkAtomic()) return;
ProcessMarkValue<MarkerBase::WriteBarrierType::kDijkstra>(
header, heap.marker(), value);
}
// static
void WriteBarrier::DijkstraMarkingBarrierRangeSlow(
HeapHandle& heap_handle, const void* first_element, size_t element_size,
size_t number_of_elements, TraceCallback trace_callback) {
auto& heap_base = HeapBase::From(heap_handle);
// GetWriteBarrierType() checks marking state.
DCHECK(heap_base.marker());
// No write barriers should be executed from atomic pause marking.
DCHECK(!heap_base.in_atomic_pause());
cppgc::subtle::DisallowGarbageCollectionScope disallow_gc_scope(heap_base);
const char* array = static_cast<const char*>(first_element);
while (number_of_elements-- > 0) {
trace_callback(&heap_base.marker()->Visitor(), array);
array += element_size;
}
}
// static
void WriteBarrier::SteeleMarkingBarrierSlowWithSentinelCheck(
const void* value) {
if (!value || value == kSentinelPointer) return;
SteeleMarkingBarrierSlow(value);
}
// static
void WriteBarrier::SteeleMarkingBarrierSlow(const void* value) {
const BasePage* page = BasePage::FromPayload(value);
const auto& heap = page->heap();
// GetWriteBarrierType() checks marking state.
DCHECK(heap.marker());
// No write barriers should be executed from atomic pause marking.
DCHECK(!heap.in_atomic_pause());
auto& header =
const_cast<HeapObjectHeader&>(page->ObjectHeaderFromInnerAddress(value));
if (!header.IsMarked<AccessMode::kAtomic>()) return;
ProcessMarkValue<MarkerBase::WriteBarrierType::kSteele>(header, heap.marker(),
value);
}
#if defined(CPPGC_YOUNG_GENERATION)
// static
void WriteBarrier::GenerationalBarrierSlow(const CagedHeapLocalData& local_data,
const AgeTable& age_table,
const void* slot,
uintptr_t value_offset,
HeapHandle* heap_handle) {
DCHECK(slot);
DCHECK(heap_handle);
DCHECK_GT(kCagedHeapReservationSize, value_offset);
// A write during atomic pause (e.g. pre-finalizer) may trigger the slow path
// of the barrier. This is a result of the order of bailouts where not marking
// results in applying the generational barrier.
auto& heap = HeapBase::From(*heap_handle);
if (heap.in_atomic_pause()) return;
if (value_offset > 0 && age_table.GetAge(value_offset) == AgeTable::Age::kOld)
return;
// Record slot.
heap.remembered_set().AddSlot((const_cast<void*>(slot)));
}
// static
void WriteBarrier::GenerationalBarrierForUncompressedSlotSlow(
const CagedHeapLocalData& local_data, const AgeTable& age_table,
const void* slot, uintptr_t value_offset, HeapHandle* heap_handle) {
DCHECK(slot);
DCHECK(heap_handle);
DCHECK_GT(kCagedHeapReservationSize, value_offset);
// A write during atomic pause (e.g. pre-finalizer) may trigger the slow path
// of the barrier. This is a result of the order of bailouts where not marking
// results in applying the generational barrier.
auto& heap = HeapBase::From(*heap_handle);
if (heap.in_atomic_pause()) return;
if (value_offset > 0 && age_table.GetAge(value_offset) == AgeTable::Age::kOld)
return;
// Record slot.
heap.remembered_set().AddUncompressedSlot((const_cast<void*>(slot)));
}
// static
void WriteBarrier::GenerationalBarrierForSourceObjectSlow(
const CagedHeapLocalData& local_data, const void* inner_pointer,
HeapHandle* heap_handle) {
DCHECK(inner_pointer);
DCHECK(heap_handle);
auto& heap = HeapBase::From(*heap_handle);
auto& object_header =
BasePage::FromInnerAddress(&heap, inner_pointer)
->ObjectHeaderFromInnerAddress<AccessMode::kAtomic>(inner_pointer);
// Record the source object.
heap.remembered_set().AddSourceObject(
const_cast<HeapObjectHeader&>(object_header));
}
#endif // CPPGC_YOUNG_GENERATION
#if V8_ENABLE_CHECKS
// static
void WriteBarrier::CheckParams(Type expected_type, const Params& params) {
CHECK_EQ(expected_type, params.type);
}
#endif // V8_ENABLE_CHECKS
#if defined(CPPGC_YOUNG_GENERATION)
// static
YoungGenerationEnabler& YoungGenerationEnabler::Instance() {
static v8::base::LeakyObject<YoungGenerationEnabler> instance;
return *instance.get();
}
void YoungGenerationEnabler::Enable() {
auto& instance = Instance();
v8::base::MutexGuard _(&instance.mutex_);
if (++instance.is_enabled_ == 1) {
// Enter the flag so that the check in the write barrier will always trigger
// when young generation is enabled.
WriteBarrier::FlagUpdater::Enter();
}
}
void YoungGenerationEnabler::Disable() {
auto& instance = Instance();
v8::base::MutexGuard _(&instance.mutex_);
DCHECK_LT(0, instance.is_enabled_);
if (--instance.is_enabled_ == 0) {
WriteBarrier::FlagUpdater::Exit();
}
}
bool YoungGenerationEnabler::IsEnabled() {
auto& instance = Instance();
v8::base::MutexGuard _(&instance.mutex_);
return instance.is_enabled_;
}
#endif // defined(CPPGC_YOUNG_GENERATION)
} // namespace internal
} // namespace cppgc
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