src/heap/read-only-heap.cc

// 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.

#include "src/heap/read-only-heap.h"

#include <cstddef>
#include <cstring>

#include "src/base/lazy-instance.h"
#include "src/base/platform/mutex.h"
#include "src/common/ptr-compr-inl.h"
#include "src/heap/basic-memory-chunk.h"
#include "src/heap/heap-write-barrier-inl.h"
#include "src/heap/memory-chunk.h"
#include "src/heap/read-only-spaces.h"
#include "src/heap/third-party/heap-api.h"
#include "src/objects/heap-object-inl.h"
#include "src/objects/objects-inl.h"
#include "src/objects/smi.h"
#include "src/snapshot/read-only-deserializer.h"
#include "src/utils/allocation.h"

namespace v8 {
namespace internal {

namespace {
// Mutex used to ensure that ReadOnlyArtifacts creation is only done once.
base::LazyMutex read_only_heap_creation_mutex_ = LAZY_MUTEX_INITIALIZER;

// Weak pointer holding ReadOnlyArtifacts. ReadOnlyHeap::SetUp creates a
// std::shared_ptr from this when it attempts to reuse it. Since all Isolates
// hold a std::shared_ptr to this, the object is destroyed when no Isolates
// remain.
base::LazyInstance<std::weak_ptr<ReadOnlyArtifacts>>::type
    read_only_artifacts_ = LAZY_INSTANCE_INITIALIZER;

std::shared_ptr<ReadOnlyArtifacts> InitializeSharedReadOnlyArtifacts() {
  std::shared_ptr<ReadOnlyArtifacts> artifacts;
  if (COMPRESS_POINTERS_BOOL) {
    artifacts = std::make_shared<PointerCompressedReadOnlyArtifacts>();
  } else {
    artifacts = std::make_shared<SingleCopyReadOnlyArtifacts>();
  }
  *read_only_artifacts_.Pointer() = artifacts;
  return artifacts;
}
}  // namespace

bool ReadOnlyHeap::IsSharedMemoryAvailable() {
  static bool shared_memory_allocation_supported =
      GetPlatformPageAllocator()->CanAllocateSharedPages();
  return shared_memory_allocation_supported;
}

// This ReadOnlyHeap instance will only be accessed by Isolates that are already
// set up. As such it doesn't need to be guarded by a mutex or shared_ptrs,
// since an already set up Isolate will hold a shared_ptr to
// read_only_artifacts_.
SoleReadOnlyHeap* SoleReadOnlyHeap::shared_ro_heap_ = nullptr;

// static
void ReadOnlyHeap::SetUp(Isolate* isolate,
                         SnapshotData* read_only_snapshot_data,
                         bool can_rehash) {
  DCHECK_NOT_NULL(isolate);

  if (IsReadOnlySpaceShared()) {
    ReadOnlyHeap* ro_heap;
    if (read_only_snapshot_data != nullptr) {
      bool read_only_heap_created = false;
      base::MutexGuard guard(read_only_heap_creation_mutex_.Pointer());
      std::shared_ptr<ReadOnlyArtifacts> artifacts =
          read_only_artifacts_.Get().lock();
      if (!artifacts) {
        artifacts = InitializeSharedReadOnlyArtifacts();
        artifacts->InitializeChecksum(read_only_snapshot_data);
        ro_heap = CreateInitalHeapForBootstrapping(isolate, artifacts);
        ro_heap->DeseralizeIntoIsolate(isolate, read_only_snapshot_data,
                                       can_rehash);
        read_only_heap_created = true;
      } else {
        // With pointer compression, there is one ReadOnlyHeap per Isolate.
        // Without PC, there is only one shared between all Isolates.
        ro_heap = artifacts->GetReadOnlyHeapForIsolate(isolate);
        isolate->SetUpFromReadOnlyArtifacts(artifacts, ro_heap);
      }
      artifacts->VerifyChecksum(read_only_snapshot_data,
                                read_only_heap_created);
      ro_heap->InitializeIsolateRoots(isolate);
    } else {
      // This path should only be taken in mksnapshot, should only be run once
      // before tearing down the Isolate that holds this ReadOnlyArtifacts and
      // is not thread-safe.
      std::shared_ptr<ReadOnlyArtifacts> artifacts =
          read_only_artifacts_.Get().lock();
      CHECK(!artifacts);
      artifacts = InitializeSharedReadOnlyArtifacts();

      ro_heap = CreateInitalHeapForBootstrapping(isolate, artifacts);
      artifacts->VerifyChecksum(read_only_snapshot_data, true);
    }
  } else {
    auto* ro_heap = new ReadOnlyHeap(new ReadOnlySpace(isolate->heap()));
    isolate->SetUpFromReadOnlyArtifacts(nullptr, ro_heap);
    if (read_only_snapshot_data != nullptr) {
      ro_heap->DeseralizeIntoIsolate(isolate, read_only_snapshot_data,
                                     can_rehash);
    }
  }
}

void ReadOnlyHeap::DeseralizeIntoIsolate(Isolate* isolate,
                                         SnapshotData* read_only_snapshot_data,
                                         bool can_rehash) {
  DCHECK_NOT_NULL(read_only_snapshot_data);
  ReadOnlyDeserializer des(isolate, read_only_snapshot_data, can_rehash);
  des.DeserializeIntoIsolate();
  InitFromIsolate(isolate);
}

void ReadOnlyHeap::OnCreateHeapObjectsComplete(Isolate* isolate) {
  DCHECK_NOT_NULL(isolate);
  InitFromIsolate(isolate);
}

// Only for compressed spaces
ReadOnlyHeap::ReadOnlyHeap(ReadOnlyHeap* ro_heap, ReadOnlySpace* ro_space)
    : read_only_space_(ro_space),
      read_only_object_cache_(ro_heap->read_only_object_cache_) {
  DCHECK(ReadOnlyHeap::IsReadOnlySpaceShared());
  DCHECK(COMPRESS_POINTERS_BOOL);
}

// static
ReadOnlyHeap* ReadOnlyHeap::CreateInitalHeapForBootstrapping(
    Isolate* isolate, std::shared_ptr<ReadOnlyArtifacts> artifacts) {
  DCHECK(IsReadOnlySpaceShared());

  std::unique_ptr<ReadOnlyHeap> ro_heap;
  auto* ro_space = new ReadOnlySpace(isolate->heap());
  if (COMPRESS_POINTERS_BOOL) {
    ro_heap.reset(new ReadOnlyHeap(ro_space));
  } else {
    std::unique_ptr<SoleReadOnlyHeap> sole_ro_heap(
        new SoleReadOnlyHeap(ro_space));
    // The global shared ReadOnlyHeap is only used without pointer compression.
    SoleReadOnlyHeap::shared_ro_heap_ = sole_ro_heap.get();
    ro_heap = std::move(sole_ro_heap);
  }
  artifacts->set_read_only_heap(std::move(ro_heap));
  isolate->SetUpFromReadOnlyArtifacts(artifacts, artifacts->read_only_heap());
  return artifacts->read_only_heap();
}

void SoleReadOnlyHeap::InitializeIsolateRoots(Isolate* isolate) {
  void* const isolate_ro_roots =
      isolate->roots_table().read_only_roots_begin().location();
  std::memcpy(isolate_ro_roots, read_only_roots_,
              kEntriesCount * sizeof(Address));
}

void SoleReadOnlyHeap::InitializeFromIsolateRoots(Isolate* isolate) {
  void* const isolate_ro_roots =
      isolate->roots_table().read_only_roots_begin().location();
  std::memcpy(read_only_roots_, isolate_ro_roots,
              kEntriesCount * sizeof(Address));
}

void ReadOnlyHeap::InitFromIsolate(Isolate* isolate) {
  DCHECK(!init_complete_);
  read_only_space_->ShrinkPages();
  if (IsReadOnlySpaceShared()) {
    InitializeFromIsolateRoots(isolate);
    std::shared_ptr<ReadOnlyArtifacts> artifacts(
        *read_only_artifacts_.Pointer());

    read_only_space()->DetachPagesAndAddToArtifacts(artifacts);
    artifacts->ReinstallReadOnlySpace(isolate);

    read_only_space_ = artifacts->shared_read_only_space();

#ifdef DEBUG
    artifacts->VerifyHeapAndSpaceRelationships(isolate);
#endif
  } else {
    read_only_space_->Seal(ReadOnlySpace::SealMode::kDoNotDetachFromHeap);
  }
  init_complete_ = true;
}

void ReadOnlyHeap::OnHeapTearDown(Heap* heap) {
  read_only_space_->TearDown(heap->memory_allocator());
  delete read_only_space_;
}

void SoleReadOnlyHeap::OnHeapTearDown(Heap* heap) {
  // Do nothing as ReadOnlyHeap is shared between all Isolates.
}

// static
void ReadOnlyHeap::PopulateReadOnlySpaceStatistics(
    SharedMemoryStatistics* statistics) {
  statistics->read_only_space_size_ = 0;
  statistics->read_only_space_used_size_ = 0;
  statistics->read_only_space_physical_size_ = 0;
  if (IsReadOnlySpaceShared()) {
    std::shared_ptr<ReadOnlyArtifacts> artifacts =
        read_only_artifacts_.Get().lock();
    if (artifacts) {
      auto* ro_space = artifacts->shared_read_only_space();
      statistics->read_only_space_size_ = ro_space->CommittedMemory();
      statistics->read_only_space_used_size_ = ro_space->Size();
      statistics->read_only_space_physical_size_ =
          ro_space->CommittedPhysicalMemory();
    }
  }
}

// static
bool ReadOnlyHeap::Contains(Address address) {
  if (V8_ENABLE_THIRD_PARTY_HEAP_BOOL) {
    return third_party_heap::Heap::InReadOnlySpace(address);
  } else {
    return BasicMemoryChunk::FromAddress(address)->InReadOnlySpace();
  }
}

// static
bool ReadOnlyHeap::Contains(HeapObject object) {
  if (V8_ENABLE_THIRD_PARTY_HEAP_BOOL) {
    return third_party_heap::Heap::InReadOnlySpace(object.address());
  } else {
    return BasicMemoryChunk::FromHeapObject(object)->InReadOnlySpace();
  }
}

Object* ReadOnlyHeap::ExtendReadOnlyObjectCache() {
  read_only_object_cache_.push_back(Smi::zero());
  return &read_only_object_cache_.back();
}

Object ReadOnlyHeap::cached_read_only_object(size_t i) const {
  DCHECK_LE(i, read_only_object_cache_.size());
  return read_only_object_cache_[i];
}

bool ReadOnlyHeap::read_only_object_cache_is_initialized() const {
  return read_only_object_cache_.size() > 0;
}

ReadOnlyHeapObjectIterator::ReadOnlyHeapObjectIterator(ReadOnlyHeap* ro_heap)
    : ReadOnlyHeapObjectIterator(ro_heap->read_only_space()) {}

ReadOnlyHeapObjectIterator::ReadOnlyHeapObjectIterator(ReadOnlySpace* ro_space)
    : ro_space_(ro_space),
      current_page_(V8_ENABLE_THIRD_PARTY_HEAP_BOOL
                        ? std::vector<ReadOnlyPage*>::iterator()
                        : ro_space->pages().begin()),
      current_addr_(V8_ENABLE_THIRD_PARTY_HEAP_BOOL
                        ? Address()
                        : (*current_page_)->GetAreaStart()) {}

HeapObject ReadOnlyHeapObjectIterator::Next() {
  if (V8_ENABLE_THIRD_PARTY_HEAP_BOOL) {
    return HeapObject();  // Unsupported
  }

  if (current_page_ == ro_space_->pages().end()) {
    return HeapObject();
  }

  ReadOnlyPage* current_page = *current_page_;
  for (;;) {
    Address end = current_page->address() + current_page->area_size() +
                  MemoryChunkLayout::ObjectStartOffsetInMemoryChunk(RO_SPACE);
    DCHECK_LE(current_addr_, end);
    if (current_addr_ == end) {
      // Progress to the next page.
      ++current_page_;
      if (current_page_ == ro_space_->pages().end()) {
        return HeapObject();
      }
      current_page = *current_page_;
      current_addr_ = current_page->GetAreaStart();
    }

    if (current_addr_ == ro_space_->top() &&
        current_addr_ != ro_space_->limit()) {
      current_addr_ = ro_space_->limit();
      continue;
    }
    HeapObject object = HeapObject::FromAddress(current_addr_);
    const int object_size = object.Size();
    current_addr_ += object_size;

    if (object.IsFreeSpaceOrFiller()) {
      continue;
    }

    DCHECK_OBJECT_SIZE(object_size);
    return object;
  }
}

}  // namespace internal
}  // namespace v8