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// Copyright 2018 The Chromium 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 "third_party/blink/renderer/platform/heap/marking_visitor.h"
#include "third_party/blink/renderer/platform/heap/heap.h"
#include "third_party/blink/renderer/platform/heap/thread_state.h"
namespace blink {
namespace {
ALWAYS_INLINE bool IsHashTableDeleteValue(const void* value) {
return value == reinterpret_cast<void*>(-1);
}
} // namespace
std::unique_ptr<MarkingVisitor> MarkingVisitor::Create(ThreadState* state,
MarkingMode mode) {
return std::make_unique<MarkingVisitor>(state, mode);
}
MarkingVisitor::MarkingVisitor(ThreadState* state, MarkingMode marking_mode)
: Visitor(state),
marking_worklist_(Heap().GetMarkingWorklist(),
WorklistTaskId::MainThread),
not_fully_constructed_worklist_(Heap().GetNotFullyConstructedWorklist(),
WorklistTaskId::MainThread),
weak_callback_worklist_(Heap().GetWeakCallbackWorklist(),
WorklistTaskId::MainThread),
marking_mode_(marking_mode) {
DCHECK(state->InAtomicMarkingPause());
#if DCHECK_IS_ON()
DCHECK(state->CheckThread());
#endif // DCHECK_IS_ON
}
MarkingVisitor::~MarkingVisitor() = default;
void MarkingVisitor::DynamicallyMarkAddress(Address address) {
BasePage* const page = PageFromObject(address);
HeapObjectHeader* const header =
page->IsLargeObjectPage()
? static_cast<LargeObjectPage*>(page)->ObjectHeader()
: static_cast<NormalPage*>(page)->FindHeaderFromAddress(address);
DCHECK(header);
DCHECK(!header->IsInConstruction());
const GCInfo* gc_info =
GCInfoTable::Get().GCInfoFromIndex(header->GcInfoIndex());
MarkHeader(header, gc_info->trace_);
}
void MarkingVisitor::ConservativelyMarkAddress(BasePage* page,
Address address) {
#if DCHECK_IS_ON()
DCHECK(page->Contains(address));
#endif
HeapObjectHeader* const header =
page->IsLargeObjectPage()
? static_cast<LargeObjectPage*>(page)->ObjectHeader()
: static_cast<NormalPage*>(page)->FindHeaderFromAddress(address);
if (!header || header->IsMarked())
return;
// Simple case for fully constructed objects.
const GCInfo* gc_info =
GCInfoTable::Get().GCInfoFromIndex(header->GcInfoIndex());
if (!header->IsInConstruction()) {
MarkHeader(header, gc_info->trace_);
return;
}
// This case is reached for not-fully-constructed objects with vtables.
// We can differentiate multiple cases:
// 1. No vtable set up. Example:
// class A : public GarbageCollected<A> { virtual void f() = 0; };
// class B : public A { B() : A(foo()) {}; };
// The vtable for A is not set up if foo() allocates and triggers a GC.
//
// 2. Vtables properly set up (non-mixin case).
// 3. Vtables not properly set up (mixin) if GC is allowed during mixin
// construction.
//
// We use a simple conservative approach for these cases as they are not
// performance critical.
MarkHeaderNoTracing(header);
Address* payload = reinterpret_cast<Address*>(header->Payload());
const size_t payload_size = header->PayloadSize();
for (size_t i = 0; i < (payload_size / sizeof(Address)); ++i) {
if (payload[i])
Heap().CheckAndMarkPointer(this, payload[i]);
}
}
void MarkingVisitor::RegisterWeakCallback(void* object, WeakCallback callback) {
// We don't want to run weak processings when taking a snapshot.
if (marking_mode_ == kSnapshotMarking)
return;
weak_callback_worklist_.Push({object, callback});
}
void MarkingVisitor::RegisterBackingStoreReference(void** slot) {
if (marking_mode_ != kGlobalMarkingWithCompaction)
return;
Heap().RegisterMovingObjectReference(
reinterpret_cast<MovableReference*>(slot));
}
void MarkingVisitor::RegisterBackingStoreCallback(void** slot,
MovingObjectCallback callback,
void* callback_data) {
if (marking_mode_ != kGlobalMarkingWithCompaction)
return;
Heap().RegisterMovingObjectCallback(reinterpret_cast<MovableReference*>(slot),
callback, callback_data);
}
bool MarkingVisitor::RegisterWeakTable(const void* closure,
EphemeronCallback iteration_callback) {
Heap().RegisterWeakTable(const_cast<void*>(closure), iteration_callback);
return true;
}
void MarkingVisitor::WriteBarrierSlow(void* value) {
if (!value || IsHashTableDeleteValue(value))
return;
ThreadState* const thread_state = ThreadState::Current();
if (!thread_state->IsIncrementalMarking())
return;
thread_state->Heap().WriteBarrier(value);
}
void MarkingVisitor::TraceMarkedBackingStoreSlow(void* value) {
if (!value)
return;
ThreadState* const thread_state = ThreadState::Current();
if (!thread_state->IsIncrementalMarking())
return;
// |value| is pointing to the start of a backing store.
HeapObjectHeader* header = HeapObjectHeader::FromPayload(value);
CHECK(header->IsMarked());
DCHECK(thread_state->CurrentVisitor());
// This check ensures that the visitor will not eagerly recurse into children
// but rather push all blink::GarbageCollected objects and only eagerly trace
// non-managed objects.
DCHECK(!thread_state->Heap().GetStackFrameDepth().IsEnabled());
// No weak handling for write barriers. Modifying weakly reachable objects
// strongifies them for the current cycle.
GCInfoTable::Get()
.GCInfoFromIndex(header->GcInfoIndex())
->trace_(thread_state->CurrentVisitor(), value);
}
} // namespace blink
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