Use clustered serialization for full snapshots.

runtime/vm/clustered_snapshot.h

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef VM_CLUSTERED_SNAPSHOT_H_
+#define VM_CLUSTERED_SNAPSHOT_H_
+
+#include "platform/assert.h"
+#include "vm/allocation.h"
+#include "vm/bitfield.h"
+#include "vm/datastream.h"
+#include "vm/exceptions.h"
+#include "vm/globals.h"
+#include "vm/growable_array.h"
+#include "vm/isolate.h"
+#include "vm/visitor.h"
+#include "vm/snapshot.h"
+#include "vm/heap.h"
+#include "vm/object.h"
+#include "vm/version.h"
+
+namespace dart {
+
+class Serializer;
+class Deserializer;
+class ObjectStore;
+
+// For full snapshots, we use a clustered snapshot format that trades longer
+// serialization time for faster deserialization time and smaller snapshots.
+// Objects are clustered by class to allow writing type information once per
+// class instead for each object, and to allow filling the objects in a tight
+// loop. The snapshot has two major sections: the first describes how to
+// allocate the objects and the second describes how to initialize them.
+// Deserialization starts by allocating a reference array large enough to hold
+// the base objects (objects already available to both the serializer and
+// deserializer) and the objects written in the snapshot. The allocation section
+// is then read for each cluster, filling the reference array. Then the
+// initialization/fill secton is read for cluster, using the indices into the
+// reference array to fill pointers. At this point, every object has been
+// touched exactly once and in order, making this approach very cache friendly.
+// Finally, each cluster is given an opportunity to perform some fix-ups that
+// require the graph has been fully loaded, such as rehashing, though most
+// clusters do not require fixups.
+
+class SerializationCluster : public ZoneAllocated {
+ public:
+  virtual ~SerializationCluster() { }
+
+  // Add [object] to the cluster and push its outgoing references.
+  virtual void Trace(Serializer* serializer, RawObject* object) = 0;
+
+  // Write the cluster type and information needed to allocate the cluster's
+  // objects. For fixed sized objects, this is just the object count. For
+  // variable sized objects, this is the object count and length of each object.
+  virtual void WriteAlloc(Serializer* serializer) = 0;
+
+  // Write the byte and reference data of the cluster's objects.
+  virtual void WriteFill(Serializer* serializer) = 0;
+};
+
+
+class DeserializationCluster : public ZoneAllocated {
+ public:
+  DeserializationCluster() : start_index_(-1), stop_index_(-1) { }
+  virtual ~DeserializationCluster() { }
+
+  // Allocate memory for all objects in the cluster and write their addresses
+  // into the ref array. Do not touch this memory.
+  virtual void ReadAlloc(Deserializer* deserializer) = 0;
+
+  // Initialize the cluster's objects. Do not touch the memory of other objects.
+  virtual void ReadFill(Deserializer* deserializer) = 0;
+
+  // Complete any action that requires the full graph to be deserialized, such
+  // as rehashing.
+  virtual void PostLoad(const Array& refs, Snapshot::Kind kind, Zone* zone) { }
+
+ protected:
+  // The range of the ref array that belongs to this cluster.
+  intptr_t start_index_;
+  intptr_t stop_index_;
+};
+
+
+class Serializer : public StackResource {
+ public:
+  Serializer(Thread* thread,
+             Snapshot::Kind kind,
+             uint8_t** buffer,
+             ReAlloc alloc,
+             intptr_t initial_size,
+             InstructionsWriter* instructions_writer_);
+  ~Serializer();
+
+  intptr_t WriteVMSnapshot(const Array& symbols, const Array& scripts);
+  void WriteFullSnapshot(intptr_t num_base_objects, ObjectStore* object_store);
+
+  void AddVMIsolateBaseObjects();
+
+  void AddBaseObject(RawObject* base_object) {
+    AssignRefNotTraced(base_object);
+    num_base_objects_++;
+  }
+
+  void AssignRefNotTraced(RawObject* object) {
+    ASSERT(next_ref_index_ != 0);
+    heap_->SetObjectId(object, next_ref_index_);
+    ASSERT(heap_->GetObjectId(object) == next_ref_index_);
+    next_ref_index_++;
+  }
+
+  void AssignRef(RawObject* object) {
+    ASSERT(next_ref_index_ != 0);
+    ASSERT(heap_->GetObjectId(object) == 1);
+    heap_->SetObjectId(object, next_ref_index_);
+    ASSERT(heap_->GetObjectId(object) == next_ref_index_);
+    next_ref_index_++;
+  }
+
+  void Push(RawObject* object) {
+    if (!object->IsHeapObject()) {
+      return;
+    }
+
+    if (object->IsCode() && !Snapshot::IncludesCode(kind_)) {
+      return;  // Do not trace, will write null.
+    }
+
+    if (object->IsSendPort()) {
+      // TODO(rmacnak): Do a better job of resetting fields in precompilation
+      // and assert this is unreachable.
+      return;  // Do not trace, will write null.
+    }
+
+    intptr_t id = heap_->GetObjectId(object);
+    if (id == 0) {
+      heap_->SetObjectId(object, 1);
+      ASSERT(heap_->GetObjectId(object) != 0);
+      stack_.Add(object);
+      num_written_objects_++;
+    }
+  }
+
+  void AddUntracedRef() {
+    num_written_objects_++;
+  }
+
+  void Trace(RawObject* object);
+
+  SerializationCluster* NewClusterForClass(intptr_t cid);
+
+  void ReserveHeader() {
+    // Make room for recording snapshot buffer size.
+    stream_.set_current(stream_.buffer() + Snapshot::kHeaderSize);
+  }
+
+  void FillHeader(Snapshot::Kind kind) {
+    int64_t* data = reinterpret_cast<int64_t*>(stream_.buffer());
+    data[Snapshot::kLengthIndex] = stream_.bytes_written();
+    data[Snapshot::kSnapshotFlagIndex] = kind;
+  }
+
+  void WriteVersionAndFeatures();
+
+  void Serialize();
+  intptr_t bytes_written() { return stream_.bytes_written(); }
+
+  // Writes raw data to the stream (basic type).
+  // sizeof(T) must be in {1,2,4,8}.
+  template <typename T>
+  void Write(T value) {
+    WriteStream::Raw<sizeof(T), T>::Write(&stream_, value);
+  }
+
+  void WriteBytes(const uint8_t* addr, intptr_t len) {
+    stream_.WriteBytes(addr, len);
+  }
+
+  void WriteRef(RawObject* object) {
+    if (!object->IsHeapObject()) {
+      Write<intptr_t>(reinterpret_cast<intptr_t>(object));

[siva, 2016/06/30 00:06:07]

How does this work when the snapshot is generated on a 64 bit system and then
read into a 32 bit system?

[rmacnak, 2016/06/30 01:39:21]

It doesn't. Added word size to the features descriptor checked on snapshot load.

+      return;
+    }
+
+    intptr_t id = heap_->GetObjectId(object);
+    if (id == 0) {
+      if (object->IsCode() && !Snapshot::IncludesCode(kind_)) {
+        WriteRef(Object::null());
+        return;
+      }
+      if (object->IsSendPort()) {
+        // TODO(rmacnak): Do a better job of resetting fields in precompilation
+        // and assert this is unreachable.
+        WriteRef(Object::null());
+        return;
+      }
+      FATAL("Missing ref");
+    }
+    Write<intptr_t>((id << 1) | 1);
+  }
+
+  void WriteTokenPosition(TokenPosition pos) {
+    Write<int32_t>(pos.SnapshotEncode());
+  }
+
+  void WriteCid(intptr_t cid) {
+    Write<int32_t>(cid);
+  }
+
+  int32_t GetTextOffset(RawInstructions* instr, RawCode* code) {
+    return instructions_writer_->GetOffsetFor(instr, code);
+  }
+
+  int32_t GetRODataOffset(RawObject* object) {
+    return instructions_writer_->GetObjectOffsetFor(object);
+  }
+
+  Snapshot::Kind kind() const { return kind_; }
+
+ private:
+  Heap* heap_;
+  Zone* zone_;
+  Snapshot::Kind kind_;
+  WriteStream stream_;
+  InstructionsWriter* instructions_writer_;
+  SerializationCluster** clusters_by_cid_;
+  GrowableArray<RawObject*> stack_;
+  intptr_t num_cids_;
+  intptr_t num_base_objects_;
+  intptr_t num_written_objects_;
+  intptr_t next_ref_index_;
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(Serializer);
+};
+
+
+class Deserializer : public StackResource {
+ public:
+  Deserializer(Thread* thread,
+               Snapshot::Kind kind,
+               const uint8_t* buffer,
+               intptr_t size,
+               const uint8_t* instructions_buffer,
+               const uint8_t* data_buffer);
+  ~Deserializer();
+
+  void ReadFullSnapshot(ObjectStore* object_store);
+  void ReadVMSnapshot();
+
+  void AddVMIsolateBaseObjects();
+
+  static void InitializeHeader(RawObject* raw,
+                               intptr_t cid,
+                               intptr_t size,
+                               bool is_vm_isolate,
+                               bool is_canonical = false);
+
+  // Reads raw data (for basic types).
+  // sizeof(T) must be in {1,2,4,8}.
+  template <typename T>
+  T Read() {
+    return ReadStream::Raw<sizeof(T), T>::Read(&stream_);
+  }
+
+  void ReadBytes(uint8_t* addr, intptr_t len) {
+    stream_.ReadBytes(addr, len);
+  }
+
+  const uint8_t* CurrentBufferAddress() const {
+    return stream_.AddressOfCurrentPosition();
+  }
+
+  void Advance(intptr_t value) {
+    stream_.Advance(value);
+  }
+
+  intptr_t PendingBytes() const {
+    return stream_.PendingBytes();
+  }
+
+  void AddBaseObject(RawObject* base_object) {
+    AssignRef(base_object);
+  }
+
+  void AssignRef(RawObject* object) {
+    ASSERT(next_ref_index_ <= num_objects_);
+    refs_->ptr()->data()[next_ref_index_] = object;
+    next_ref_index_++;
+  }
+
+  RawObject* Ref(intptr_t index) const {
+    ASSERT(index > 0);
+    ASSERT(index <= num_objects_);
+    return refs_->ptr()->data()[index];
+  }
+
+  RawObject* ReadRef() {
+    intptr_t index = Read<intptr_t>();
+    if ((index & 1) == 0) {
+      return reinterpret_cast<RawSmi*>(index);

[siva, 2016/06/30 00:06:07]

See question about reading a snapshot generated on a 64 bit system and read on a
32 bit system.

+    }
+    return Ref(index >> 1);
+  }
+
+  TokenPosition ReadTokenPosition() {
+    return TokenPosition::SnapshotDecode(Read<int32_t>());
+  }
+
+  intptr_t ReadCid() {
+    return Read<int32_t>();
+  }
+
+  uword GetInstructionsAt(int32_t offset) {
+    return instructions_reader_->GetInstructionsAt(offset);
+  }
+
+  RawObject* GetObjectAt(int32_t offset) {
+    return instructions_reader_->GetObjectAt(offset);
+  }
+
+  RawApiError* VerifyVersionAndFeatures();
+
+  void Prepare();
+  void Deserialize();
+
+  DeserializationCluster* ReadCluster();
+
+  intptr_t next_index() const { return next_ref_index_; }
+  Heap* heap() const { return heap_; }
+  Snapshot::Kind kind() const { return kind_; }
+
+ private:
+  Heap* heap_;
+  Zone* zone_;
+  Snapshot::Kind kind_;
+  ReadStream stream_;
+  InstructionsReader* instructions_reader_;
+  intptr_t num_objects_;
+  intptr_t num_clusters_;
+  RawArray* refs_;
+  intptr_t next_ref_index_;
+  DeserializationCluster** clusters_;
+};
+
+
+class FullSnapshotWriter {
+ public:
+  static const intptr_t kInitialSize = 64 * KB;
+  FullSnapshotWriter(Snapshot::Kind kind,
+                     uint8_t** vm_isolate_snapshot_buffer,
+                     uint8_t** isolate_snapshot_buffer,
+                     ReAlloc alloc,
+                     InstructionsWriter* instructions_writer);
+  ~FullSnapshotWriter();
+
+  uint8_t** vm_isolate_snapshot_buffer() {
+    return vm_isolate_snapshot_buffer_;
+  }
+
+  uint8_t** isolate_snapshot_buffer() {
+    return isolate_snapshot_buffer_;
+  }
+
+  Thread* thread() const { return thread_; }
+  Zone* zone() const { return thread_->zone(); }
+  Isolate* isolate() const { return thread_->isolate(); }
+  Heap* heap() const { return isolate()->heap(); }
+
+  // Writes a full snapshot of the Isolate.
+  void WriteFullSnapshot();
+
+  intptr_t VmIsolateSnapshotSize() const {
+    return vm_isolate_snapshot_size_;
+  }
+  intptr_t IsolateSnapshotSize() const {
+    return isolate_snapshot_size_;
+  }
+
+ private:
+  // Writes a snapshot of the VM Isolate.
+  intptr_t WriteVmIsolateSnapshot();
+
+  // Writes a full snapshot of a regular Dart Isolate.
+  void WriteIsolateFullSnapshot(intptr_t num_base_objects);
+
+  Thread* thread_;
+  Snapshot::Kind kind_;
+  uint8_t** vm_isolate_snapshot_buffer_;
+  uint8_t** isolate_snapshot_buffer_;
+  ReAlloc alloc_;
+  intptr_t vm_isolate_snapshot_size_;
+  intptr_t isolate_snapshot_size_;
+  ForwardList* forward_list_;
+  InstructionsWriter* instructions_writer_;
+  Array& scripts_;
+  Array& saved_symbol_table_;
+  Array& new_vm_symbol_table_;
+
+  DISALLOW_COPY_AND_ASSIGN(FullSnapshotWriter);
+};
+
+
+class VmIsolateSnapshotReader {
+ public:
+  VmIsolateSnapshotReader(Snapshot::Kind kind,
+                          const uint8_t* buffer,
+                          intptr_t size,
+                          const uint8_t* instructions_buffer,
+                          const uint8_t* data_buffer,
+                          Thread* thread) :
+      kind_(kind),
+      thread_(thread),
+      buffer_(buffer),
+      size_(size),
+      instructions_buffer_(instructions_buffer),
+      data_buffer_(data_buffer) {
+    thread->isolate()->set_compilation_allowed(kind != Snapshot::kAppNoJIT);
+  }
+
+  ~VmIsolateSnapshotReader() { }
+
+  RawApiError* ReadVmIsolateSnapshot();
+
+ private:
+  Snapshot::Kind kind_;
+  Thread* thread_;
+  const uint8_t* buffer_;
+  intptr_t size_;
+  const uint8_t* instructions_buffer_;
+  const uint8_t* data_buffer_;
+
+  DISALLOW_COPY_AND_ASSIGN(VmIsolateSnapshotReader);
+};
+
+
+class IsolateSnapshotReader {
+ public:
+  IsolateSnapshotReader(Snapshot::Kind kind,
+                              const uint8_t* buffer,
+                              intptr_t size,
+                              const uint8_t* instructions_buffer,
+                              const uint8_t* data_buffer,
+                              Thread* thread) :
+      kind_(kind),
+      thread_(thread),
+      buffer_(buffer),
+      size_(size),
+      instructions_buffer_(instructions_buffer),
+      data_buffer_(data_buffer) {
+    thread->isolate()->set_compilation_allowed(kind != Snapshot::kAppNoJIT);
+  }
+
+  ~IsolateSnapshotReader() {}
+
+  RawApiError* ReadFullSnapshot();
+
+ private:
+  Snapshot::Kind kind_;
+  Thread* thread_;
+  const uint8_t* buffer_;
+  intptr_t size_;
+  const uint8_t* instructions_buffer_;
+  const uint8_t* data_buffer_;
+
+  DISALLOW_COPY_AND_ASSIGN(IsolateSnapshotReader);
+};
+
+}  // namespace dart
+
+#endif  // VM_CLUSTERED_SNAPSHOT_H_