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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/sweeper.h"
#include <vector>
#include "src/heap/cppgc/free-list.h"
#include "src/heap/cppgc/globals.h"
#include "src/heap/cppgc/heap-object-header-inl.h"
#include "src/heap/cppgc/heap-object-header.h"
#include "src/heap/cppgc/heap-page.h"
#include "src/heap/cppgc/heap-space.h"
#include "src/heap/cppgc/heap-visitor.h"
#include "src/heap/cppgc/object-start-bitmap-inl.h"
#include "src/heap/cppgc/object-start-bitmap.h"
#include "src/heap/cppgc/raw-heap.h"
#include "src/heap/cppgc/sanitizers.h"
namespace cppgc {
namespace internal {
namespace {
class ObjectStartBitmapVerifier
: private HeapVisitor<ObjectStartBitmapVerifier> {
friend class HeapVisitor<ObjectStartBitmapVerifier>;
public:
void Verify(RawHeap* heap) { Traverse(heap); }
private:
bool VisitNormalPage(NormalPage* page) {
// Remember bitmap and reset previous pointer.
bitmap_ = &page->object_start_bitmap();
prev_ = nullptr;
return false;
}
bool VisitHeapObjectHeader(HeapObjectHeader* header) {
if (header->IsLargeObject()) return true;
auto* raw_header = reinterpret_cast<ConstAddress>(header);
CHECK(bitmap_->CheckBit(raw_header));
if (prev_) {
CHECK_EQ(prev_, bitmap_->FindHeader(raw_header - 1));
}
prev_ = header;
return true;
}
ObjectStartBitmap* bitmap_ = nullptr;
HeapObjectHeader* prev_ = nullptr;
};
struct SpaceState {
BaseSpace::Pages unswept_pages;
};
using SpaceStates = std::vector<SpaceState>;
bool SweepNormalPage(NormalPage* page) {
constexpr auto kAtomicAccess = HeapObjectHeader::AccessMode::kAtomic;
auto* space = NormalPageSpace::From(page->space());
ObjectStartBitmap& bitmap = page->object_start_bitmap();
bitmap.Clear();
Address start_of_gap = page->PayloadStart();
for (Address begin = page->PayloadStart(), end = page->PayloadEnd();
begin != end;) {
HeapObjectHeader* header = reinterpret_cast<HeapObjectHeader*>(begin);
const size_t size = header->GetSize();
// Check if this is a free list entry.
if (header->IsFree<kAtomicAccess>()) {
SET_MEMORY_INACCESIBLE(header, std::min(kFreeListEntrySize, size));
begin += size;
continue;
}
// Check if object is not marked (not reachable).
if (!header->IsMarked<kAtomicAccess>()) {
header->Finalize();
SET_MEMORY_INACCESIBLE(header, size);
begin += size;
continue;
}
// The object is alive.
const Address header_address = reinterpret_cast<Address>(header);
if (start_of_gap != header_address) {
space->AddToFreeList(start_of_gap,
static_cast<size_t>(header_address - start_of_gap));
}
header->Unmark<kAtomicAccess>();
bitmap.SetBit(begin);
begin += size;
start_of_gap = begin;
}
if (start_of_gap != page->PayloadStart() &&
start_of_gap != page->PayloadEnd()) {
space->AddToFreeList(
start_of_gap, static_cast<size_t>(page->PayloadEnd() - start_of_gap));
}
const bool is_empty = (start_of_gap == page->PayloadStart());
return is_empty;
}
// This visitor:
// - resets linear allocation buffers and clears free lists for all spaces;
// - moves all Heap pages to local Sweeper's state (SpaceStates).
class PrepareForSweepVisitor final
: public HeapVisitor<PrepareForSweepVisitor> {
public:
explicit PrepareForSweepVisitor(SpaceStates* states) : states_(states) {}
bool VisitNormalPageSpace(NormalPageSpace* space) {
space->ResetLinearAllocationBuffer();
space->free_list().Clear();
(*states_)[space->index()].unswept_pages = space->RemoveAllPages();
return true;
}
bool VisitLargePageSpace(LargePageSpace* space) {
(*states_)[space->index()].unswept_pages = space->RemoveAllPages();
return true;
}
private:
SpaceStates* states_;
};
class MutatorThreadSweepVisitor final
: private HeapVisitor<MutatorThreadSweepVisitor> {
friend class HeapVisitor<MutatorThreadSweepVisitor>;
public:
explicit MutatorThreadSweepVisitor(SpaceStates* space_states) {
for (SpaceState& state : *space_states) {
for (BasePage* page : state.unswept_pages) {
Traverse(page);
}
state.unswept_pages.clear();
}
}
private:
bool VisitNormalPage(NormalPage* page) {
const bool is_empty = SweepNormalPage(page);
if (is_empty) {
NormalPage::Destroy(page);
} else {
page->space()->AddPage(page);
}
return true;
}
bool VisitLargePage(LargePage* page) {
if (page->ObjectHeader()->IsMarked()) {
page->space()->AddPage(page);
} else {
page->ObjectHeader()->Finalize();
LargePage::Destroy(page);
}
return true;
}
};
} // namespace
class Sweeper::SweeperImpl final {
public:
explicit SweeperImpl(RawHeap* heap) : heap_(heap) {
space_states_.resize(heap_->size());
}
void Start(Config config) {
is_in_progress_ = true;
#if DEBUG
ObjectStartBitmapVerifier().Verify(heap_);
#endif
PrepareForSweepVisitor(&space_states_).Traverse(heap_);
if (config == Config::kAtomic) {
Finish();
} else {
DCHECK_EQ(Config::kIncrementalAndConcurrent, config);
// TODO(chromium:1056170): Schedule concurrent sweeping.
}
}
void Finish() {
if (!is_in_progress_) return;
MutatorThreadSweepVisitor s(&space_states_);
is_in_progress_ = false;
}
private:
SpaceStates space_states_;
RawHeap* heap_;
bool is_in_progress_ = false;
};
Sweeper::Sweeper(RawHeap* heap) : impl_(std::make_unique<SweeperImpl>(heap)) {}
Sweeper::~Sweeper() = default;
void Sweeper::Start(Config config) { impl_->Start(config); }
void Sweeper::Finish() { impl_->Finish(); }
} // namespace internal
} // namespace cppgc
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