[snapshot] support multiple contexts in the same snapshot.

R=jochen@chromium.org, vogelheim@chromium.org
BUG=chromium:617892

Review-Url: https://codereview.chromium.org/2055203002
Cr-Commit-Position: refs/heads/master@{#37008}

include/v8.h

@@ -6787,8 +6787,9 @@ class SnapshotCreator {
 
   /**
    * Add a context to be included in the snapshot blob.
+   * \returns the index of the context in the snapshot blob.
    */
-  void AddContext(Local<Context> context);
+  size_t AddContext(Local<Context> context);
 
   /**
    * Created a snapshot data blob.
@@ -7092,7 +7093,8 @@ class V8_EXPORT Context {
   static Local<Context> New(
       Isolate* isolate, ExtensionConfiguration* extensions = NULL,
       Local<ObjectTemplate> global_template = Local<ObjectTemplate>(),
-      Local<Value> global_object = Local<Value>());
+      Local<Value> global_object = Local<Value>(),
+      size_t context_snapshot_index = 0);
 
   /**
    * Sets the security token for the context.  To access an object in

src/api.cc

@@ -429,13 +429,15 @@ Isolate* SnapshotCreator::GetIsolate() {
   return SnapshotCreatorData::cast(data_)->isolate_;
 }
 
-void SnapshotCreator::AddContext(Local<Context> context) {
+size_t SnapshotCreator::AddContext(Local<Context> context) {
   DCHECK(!context.IsEmpty());
   SnapshotCreatorData* data = SnapshotCreatorData::cast(data_);
   DCHECK(!data->created_);
   Isolate* isolate = data->isolate_;
   CHECK_EQ(isolate, context->GetIsolate());
+  size_t index = static_cast<int>(data->contexts_.Size());
   data->contexts_.Append(context);
+  return index;
 }
 
 StartupData SnapshotCreator::CreateBlob(
@@ -464,13 +466,25 @@ StartupData SnapshotCreator::CreateBlob(
   i::StartupSerializer startup_serializer(isolate, function_code_handling);
   startup_serializer.SerializeStrongReferences();
 
-  i::PartialSerializer context_serializer(isolate, &startup_serializer);
-  context_serializer.Serialize(&contexts[0]);
+  // Serialize each context with a new partial serializer.
+  i::List<i::SnapshotData*> context_snapshots(num_contexts);
+  for (int i = 0; i < num_contexts; i++) {
+    i::PartialSerializer partial_serializer(isolate, &startup_serializer);
+    partial_serializer.Serialize(&contexts[i]);
+    context_snapshots.Add(new i::SnapshotData(&partial_serializer));
+  }
+
   startup_serializer.SerializeWeakReferencesAndDeferred();
+  i::SnapshotData startup_snapshot(&startup_serializer);
+  StartupData result =
+      i::Snapshot::CreateSnapshotBlob(&startup_snapshot, &context_snapshots);
 
+  // Delete heap-allocated context snapshot instances.
+  for (const auto& context_snapshot : context_snapshots) {
+    delete context_snapshot;
+  }
   data->created_ = true;
-  return i::Snapshot::CreateSnapshotBlob(&startup_serializer,
-                                         &context_serializer);
+  return result;
 }
 
 StartupData V8::CreateSnapshotDataBlob(const char* embedded_source) {
@@ -5532,11 +5546,10 @@ const char* v8::V8::GetVersion() {
   return i::Version::GetVersion();
 }
 
-
 static i::Handle<i::Context> CreateEnvironment(
     i::Isolate* isolate, v8::ExtensionConfiguration* extensions,
     v8::Local<ObjectTemplate> global_template,
-    v8::Local<Value> maybe_global_proxy) {
+    v8::Local<Value> maybe_global_proxy, size_t context_snapshot_index) {
   i::Handle<i::Context> env;
 
   // Enter V8 via an ENTER_V8 scope.
@@ -5581,7 +5594,7 @@ static i::Handle<i::Context> CreateEnvironment(
     }
     // Create the environment.
     env = isolate->bootstrapper()->CreateEnvironment(
-        maybe_proxy, proxy_template, extensions);
+        maybe_proxy, proxy_template, extensions, context_snapshot_index);
 
     // Restore the access check info on the global template.
     if (!global_template.IsEmpty()) {
@@ -5601,14 +5614,16 @@ static i::Handle<i::Context> CreateEnvironment(
 Local<Context> v8::Context::New(v8::Isolate* external_isolate,
                                 v8::ExtensionConfiguration* extensions,
                                 v8::Local<ObjectTemplate> global_template,
-                                v8::Local<Value> global_object) {
+                                v8::Local<Value> global_object,
+                                size_t context_snapshot_index) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(external_isolate);
   LOG_API(isolate, Context, New);
   i::HandleScope scope(isolate);
   ExtensionConfiguration no_extensions;
   if (extensions == NULL) extensions = &no_extensions;
   i::Handle<i::Context> env =
-      CreateEnvironment(isolate, extensions, global_template, global_object);
+      CreateEnvironment(isolate, extensions, global_template, global_object,
+                        context_snapshot_index);
   if (env.is_null()) {
     if (isolate->has_pending_exception()) {
       isolate->OptionalRescheduleException(true);

src/bootstrapper.cc

@@ -138,7 +138,7 @@ class Genesis BASE_EMBEDDED {
  public:
   Genesis(Isolate* isolate, MaybeHandle<JSGlobalProxy> maybe_global_proxy,
           v8::Local<v8::ObjectTemplate> global_proxy_template,
-          v8::ExtensionConfiguration* extensions,
+          v8::ExtensionConfiguration* extensions, size_t context_snapshot_index,
           GlobalContextType context_type);
   ~Genesis() { }
 
@@ -324,10 +324,11 @@ void Bootstrapper::Iterate(ObjectVisitor* v) {
 Handle<Context> Bootstrapper::CreateEnvironment(
     MaybeHandle<JSGlobalProxy> maybe_global_proxy,
     v8::Local<v8::ObjectTemplate> global_proxy_template,
-    v8::ExtensionConfiguration* extensions, GlobalContextType context_type) {
+    v8::ExtensionConfiguration* extensions, size_t context_snapshot_index,
+    GlobalContextType context_type) {
   HandleScope scope(isolate_);
   Genesis genesis(isolate_, maybe_global_proxy, global_proxy_template,
-                  extensions, context_type);
+                  extensions, context_snapshot_index, context_type);
   Handle<Context> env = genesis.result();
   if (env.is_null() ||
       (context_type != THIN_CONTEXT && !InstallExtensions(env, extensions))) {
@@ -3800,7 +3801,7 @@ Genesis::Genesis(Isolate* isolate,
                  MaybeHandle<JSGlobalProxy> maybe_global_proxy,
                  v8::Local<v8::ObjectTemplate> global_proxy_template,
                  v8::ExtensionConfiguration* extensions,
-                 GlobalContextType context_type)
+                 size_t context_snapshot_index, GlobalContextType context_type)
     : isolate_(isolate), active_(isolate->bootstrapper()) {
   NoTrackDoubleFieldsForSerializerScope disable_scope(isolate);
   result_ = Handle<Context>::null();
@@ -3829,7 +3830,8 @@ Genesis::Genesis(Isolate* isolate,
   // a snapshot. Otherwise we have to build the context from scratch.
   // Also create a context from scratch to expose natives, if required by flag.
   if (!isolate->initialized_from_snapshot() ||
-      !Snapshot::NewContextFromSnapshot(isolate, global_proxy)
+      !Snapshot::NewContextFromSnapshot(isolate, global_proxy,
+                                        context_snapshot_index)
            .ToHandle(&native_context_)) {
     native_context_ = Handle<Context>();
   }

src/bootstrapper.h

@@ -79,7 +79,7 @@ class Bootstrapper final {
   Handle<Context> CreateEnvironment(
       MaybeHandle<JSGlobalProxy> maybe_global_proxy,
       v8::Local<v8::ObjectTemplate> global_object_template,
-      v8::ExtensionConfiguration* extensions,
+      v8::ExtensionConfiguration* extensions, size_t context_snapshot_index,
       GlobalContextType context_type = FULL_CONTEXT);
 
   // Detach the environment from its outer global object.

src/debug/debug.cc

@@ -536,9 +536,13 @@ bool Debug::Load() {
   // Create the debugger context.
   HandleScope scope(isolate_);
   ExtensionConfiguration no_extensions;
+  // TODO(yangguo): we rely on the fact that first context snapshot is usable
+  //                as debug context. This dependency is gone once we remove
+  //                debug context completely.
+  static const int kFirstContextSnapshotIndex = 0;
   Handle<Context> context = isolate_->bootstrapper()->CreateEnvironment(
       MaybeHandle<JSGlobalProxy>(), v8::Local<ObjectTemplate>(), &no_extensions,
-      DEBUG_CONTEXT);
+      kFirstContextSnapshotIndex, DEBUG_CONTEXT);
 
   // Fail if no context could be created.
   if (context.is_null()) return false;

src/snapshot/partial-serializer.cc

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "src/snapshot/partial-serializer.h"
+#include "src/snapshot/startup-serializer.h"
 
 #include "src/objects-inl.h"
 
@@ -10,10 +11,8 @@ namespace v8 {
 namespace internal {
 
 PartialSerializer::PartialSerializer(Isolate* isolate,
-                                     Serializer* startup_snapshot_serializer)
-    : Serializer(isolate),
-      startup_serializer_(startup_snapshot_serializer),
-      next_partial_cache_index_(0) {
+                                     StartupSerializer* startup_serializer)
+    : Serializer(isolate), startup_serializer_(startup_serializer) {
   InitializeCodeAddressMap();
 }
 
@@ -61,7 +60,7 @@ void PartialSerializer::SerializeObject(HeapObject* obj, HowToCode how_to_code,
   if (ShouldBeInThePartialSnapshotCache(obj)) {
     FlushSkip(skip);
 
-    int cache_index = PartialSnapshotCacheIndex(obj);
+    int cache_index = startup_serializer_->PartialSnapshotCacheIndex(obj);
     sink_.Put(kPartialSnapshotCache + how_to_code + where_to_point,
               "PartialSnapshotCache");
     sink_.PutInt(cache_index, "partial_snapshot_cache_index");
@@ -93,19 +92,6 @@ void PartialSerializer::SerializeObject(HeapObject* obj, HowToCode how_to_code,
   serializer.Serialize();
 }
 
-int PartialSerializer::PartialSnapshotCacheIndex(HeapObject* heap_object) {
-  int index = partial_cache_index_map_.LookupOrInsert(
-      heap_object, next_partial_cache_index_);
-  if (index == PartialCacheIndexMap::kInvalidIndex) {
-    // This object is not part of the partial snapshot cache yet. Add it to the
-    // startup snapshot so we can refer to it via partial snapshot index from
-    // the partial snapshot.
-    startup_serializer_->VisitPointer(reinterpret_cast<Object**>(&heap_object));
-    return next_partial_cache_index_++;
-  }
-  return index;
-}
-
 bool PartialSerializer::ShouldBeInThePartialSnapshotCache(HeapObject* o) {
   // Scripts should be referred only through shared function infos.  We can't
   // allow them to be part of the partial snapshot because they contain a

src/snapshot/partial-serializer.h

@@ -11,9 +11,11 @@
 namespace v8 {
 namespace internal {
 
+class StartupSerializer;
+
 class PartialSerializer : public Serializer {
  public:
-  PartialSerializer(Isolate* isolate, Serializer* startup_snapshot_serializer);
+  PartialSerializer(Isolate* isolate, StartupSerializer* startup_serializer);
 
   ~PartialSerializer() override;
 
@@ -21,36 +23,12 @@ class PartialSerializer : public Serializer {
   void Serialize(Object** o);
 
  private:
-  class PartialCacheIndexMap : public AddressMapBase {
-   public:
-    PartialCacheIndexMap() : map_(base::HashMap::PointersMatch) {}
-
-    static const int kInvalidIndex = -1;
-
-    // Lookup object in the map. Return its index if found, or create
-    // a new entry with new_index as value, and return kInvalidIndex.
-    int LookupOrInsert(HeapObject* obj, int new_index) {
-      base::HashMap::Entry* entry = LookupEntry(&map_, obj, false);
-      if (entry != NULL) return GetValue(entry);
-      SetValue(LookupEntry(&map_, obj, true), static_cast<uint32_t>(new_index));
-      return kInvalidIndex;
-    }
-
-   private:
-    base::HashMap map_;
-
-    DISALLOW_COPY_AND_ASSIGN(PartialCacheIndexMap);
-  };
-
   void SerializeObject(HeapObject* o, HowToCode how_to_code,
                        WhereToPoint where_to_point, int skip) override;
 
-  int PartialSnapshotCacheIndex(HeapObject* o);
   bool ShouldBeInThePartialSnapshotCache(HeapObject* o);
 
-  Serializer* startup_serializer_;
-  PartialCacheIndexMap partial_cache_index_map_;
-  int next_partial_cache_index_;
+  StartupSerializer* startup_serializer_;
   DISALLOW_COPY_AND_ASSIGN(PartialSerializer);
 };
 

src/snapshot/snapshot.h

@@ -16,6 +16,41 @@ class Isolate;
 class PartialSerializer;
 class StartupSerializer;
 
+// Wrapper around reservation sizes and the serialization payload.
+class SnapshotData : public SerializedData {
+ public:
+  // Used when producing.
+  explicit SnapshotData(const Serializer* serializer);
+
+  // Used when consuming.
+  explicit SnapshotData(const Vector<const byte> snapshot)
+      : SerializedData(const_cast<byte*>(snapshot.begin()), snapshot.length()) {
+    CHECK(IsSane());
+  }
+
+  Vector<const Reservation> Reservations() const;
+  Vector<const byte> Payload() const;
+
+  Vector<const byte> RawData() const {
+    return Vector<const byte>(data_, size_);
+  }
+
+ private:
+  bool IsSane();
+
+  // The data header consists of uint32_t-sized entries:
+  // [0] magic number and external reference count
+  // [1] version hash
+  // [2] number of reservation size entries
+  // [3] payload length
+  // ... reservations
+  // ... serialized payload
+  static const int kCheckSumOffset = kMagicNumberOffset + kInt32Size;
+  static const int kNumReservationsOffset = kCheckSumOffset + kInt32Size;
+  static const int kPayloadLengthOffset = kNumReservationsOffset + kInt32Size;
+  static const int kHeaderSize = kPayloadLengthOffset + kInt32Size;
+};
+
 class Snapshot : public AllStatic {
  public:
   // Initialize the Isolate from the internal snapshot. Returns false if no
@@ -23,7 +58,8 @@ class Snapshot : public AllStatic {
   static bool Initialize(Isolate* isolate);
   // Create a new context using the internal partial snapshot.
   static MaybeHandle<Context> NewContextFromSnapshot(
-      Isolate* isolate, Handle<JSGlobalProxy> global_proxy);
+      Isolate* isolate, Handle<JSGlobalProxy> global_proxy,
+      size_t context_index);
 
   static bool HaveASnapshotToStartFrom(Isolate* isolate);
 
@@ -36,32 +72,44 @@ class Snapshot : public AllStatic {
   static const v8::StartupData* DefaultSnapshotBlob();
 
   static v8::StartupData CreateSnapshotBlob(
-      const StartupSerializer* startup_serializer,
-      const PartialSerializer* context_serializer);
+      const SnapshotData* startup_snapshot,
+      const List<SnapshotData*>* context_snapshots);
 
 #ifdef DEBUG
   static bool SnapshotIsValid(v8::StartupData* snapshot_blob);
 #endif  // DEBUG
 
  private:
+  static int ExtractNumContexts(const v8::StartupData* data);
   static Vector<const byte> ExtractStartupData(const v8::StartupData* data);
-  static Vector<const byte> ExtractContextData(const v8::StartupData* data);
+  static Vector<const byte> ExtractContextData(const v8::StartupData* data,
+                                               int index);
 
   // Snapshot blob layout:
   // [0 - 5] pre-calculated first page sizes for paged spaces
-  // [6] serialized start up data length
-  // ... serialized start up data
-  // ... serialized context data
+  // [6] number of contexts N
+  // [7] offset to context 0
+  // [8] offset to context 1
+  // ...
+  // ... offset to context N - 1
+  // ... startup snapshot data
+  // ... context 0 snapshot data
+  // ... context 1 snapshot data
 
   static const int kNumPagedSpaces = LAST_PAGED_SPACE - FIRST_PAGED_SPACE + 1;
 
   static const int kFirstPageSizesOffset = 0;
-  static const int kStartupLengthOffset =
+  static const int kNumberOfContextsOffset =
       kFirstPageSizesOffset + kNumPagedSpaces * kInt32Size;
-  static const int kStartupDataOffset = kStartupLengthOffset + kInt32Size;
+  static const int kFirstContextOffsetOffset =
+      kNumberOfContextsOffset + kInt32Size;
+
+  static int StartupSnapshotOffset(int num_contexts) {
+    return kFirstContextOffsetOffset + num_contexts * kInt32Size;
+  }
 
-  static int ContextOffset(int startup_length) {
-    return kStartupDataOffset + startup_length;
+  static int ContextSnapshotOffsetOffset(int index) {
+    return kFirstContextOffsetOffset + index * kInt32Size;
   }
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(Snapshot);
@@ -71,41 +119,6 @@ class Snapshot : public AllStatic {
 void SetSnapshotFromFile(StartupData* snapshot_blob);
 #endif
 
-// Wrapper around reservation sizes and the serialization payload.
-class SnapshotData : public SerializedData {
- public:
-  // Used when producing.
-  explicit SnapshotData(const Serializer* serializer);
-
-  // Used when consuming.
-  explicit SnapshotData(const Vector<const byte> snapshot)
-      : SerializedData(const_cast<byte*>(snapshot.begin()), snapshot.length()) {
-    CHECK(IsSane());
-  }
-
-  Vector<const Reservation> Reservations() const;
-  Vector<const byte> Payload() const;
-
-  Vector<const byte> RawData() const {
-    return Vector<const byte>(data_, size_);
-  }
-
- private:
-  bool IsSane();
-
-  // The data header consists of uint32_t-sized entries:
-  // [0] magic number and external reference count
-  // [1] version hash
-  // [2] number of reservation size entries
-  // [3] payload length
-  // ... reservations
-  // ... serialized payload
-  static const int kCheckSumOffset = kMagicNumberOffset + kInt32Size;
-  static const int kNumReservationsOffset = kCheckSumOffset + kInt32Size;
-  static const int kPayloadLengthOffset = kNumReservationsOffset + kInt32Size;
-  static const int kHeaderSize = kPayloadLengthOffset + kInt32Size;
-};
-
 }  // namespace internal
 }  // namespace v8
 

src/snapshot/startup-serializer.cc

@@ -90,6 +90,17 @@ void StartupSerializer::SerializeWeakReferencesAndDeferred() {
   Pad();
 }
 
+int StartupSerializer::PartialSnapshotCacheIndex(HeapObject* heap_object) {
+  int index;
+  if (!partial_cache_index_map_.LookupOrInsert(heap_object, &index)) {
+    // This object is not part of the partial snapshot cache yet. Add it to the
+    // startup snapshot so we can refer to it via partial snapshot index from
+    // the partial snapshot.
+    VisitPointer(reinterpret_cast<Object**>(&heap_object));
+  }
+  return index;
+}
+
 void StartupSerializer::Synchronize(VisitorSynchronization::SyncTag tag) {
   // We expect the builtins tag after builtins have been serialized.
   DCHECK(!serializing_builtins_ || tag == VisitorSynchronization::kBuiltins);

src/snapshot/startup-serializer.h

@@ -27,7 +27,34 @@ class StartupSerializer : public Serializer {
   void SerializeStrongReferences();
   void SerializeWeakReferencesAndDeferred();
 
+  int PartialSnapshotCacheIndex(HeapObject* o);
+
  private:
+  class PartialCacheIndexMap : public AddressMapBase {
+   public:
+    PartialCacheIndexMap()
+        : map_(base::HashMap::PointersMatch), next_index_(0) {}
+
+    // Lookup object in the map. Return its index if found, or create
+    // a new entry with new_index as value, and return kInvalidIndex.
+    bool LookupOrInsert(HeapObject* obj, int* index_out) {
+      base::HashMap::Entry* entry = LookupEntry(&map_, obj, false);
+      if (entry != NULL) {
+        *index_out = GetValue(entry);
+        return true;
+      }
+      *index_out = next_index_;
+      SetValue(LookupEntry(&map_, obj, true), next_index_++);
+      return false;
+    }
+
+   private:
+    base::HashMap map_;
+    int next_index_;
+
+    DISALLOW_COPY_AND_ASSIGN(PartialCacheIndexMap);
+  };
+
   // The StartupSerializer has to serialize the root array, which is slightly
   // different.
   void VisitPointers(Object** start, Object** end) override;
@@ -45,6 +72,7 @@ class StartupSerializer : public Serializer {
   bool serializing_builtins_;
   bool serializing_immortal_immovables_roots_;
   std::bitset<Heap::kStrongRootListLength> root_has_been_serialized_;
+  PartialCacheIndexMap partial_cache_index_map_;
   DISALLOW_COPY_AND_ASSIGN(StartupSerializer);
 };
 

test/cctest/test-serialize.cc

@@ -1882,6 +1882,71 @@ TEST(CodeSerializerCell) {
 }
 #endif  // V8_TARGET_ARCH_X64
 
+TEST(SnapshotCreatorMultipleContexts) {
+  DisableTurbofan();
+  v8::StartupData blob;
+  {
+    v8::SnapshotCreator creator;
+    v8::Isolate* isolate = creator.GetIsolate();
+    {
+      v8::HandleScope handle_scope(isolate);
+      v8::Local<v8::Context> context = v8::Context::New(isolate);
+      v8::Context::Scope context_scope(context);
+      CompileRun("var f = function() { return 1; }");
+      CHECK_EQ(0, creator.AddContext(context));
+    }
+    {
+      v8::HandleScope handle_scope(isolate);
+      v8::Local<v8::Context> context = v8::Context::New(isolate);
+      v8::Context::Scope context_scope(context);
+      CompileRun("var f = function() { return 2; }");
+      CHECK_EQ(1, creator.AddContext(context));
+    }
+    {
+      v8::HandleScope handle_scope(isolate);
+      v8::Local<v8::Context> context = v8::Context::New(isolate);
+      CHECK_EQ(2, creator.AddContext(context));
+    }
+    blob =
+        creator.CreateBlob(v8::SnapshotCreator::FunctionCodeHandling::kClear);
+  }
+
+  v8::Isolate::CreateParams params;
+  params.snapshot_blob = &blob;
+  params.array_buffer_allocator = CcTest::array_buffer_allocator();
+  v8::Isolate* isolate = v8::Isolate::New(params);
+  {
+    v8::Isolate::Scope isolate_scope(isolate);
+    v8::ExtensionConfiguration* no_extension = nullptr;
+    v8::Local<v8::ObjectTemplate> no_template = v8::Local<v8::ObjectTemplate>();
+    v8::Local<v8::Value> no_object = v8::Local<v8::Value>();
+    {
+      v8::HandleScope handle_scope(isolate);
+      v8::Local<v8::Context> context =
+          v8::Context::New(isolate, no_extension, no_template, no_object, 0);
+      v8::Context::Scope context_scope(context);
+      ExpectInt32("f()", 1);
+    }
+    {
+      v8::HandleScope handle_scope(isolate);
+      v8::Local<v8::Context> context =
+          v8::Context::New(isolate, no_extension, no_template, no_object, 1);
+      v8::Context::Scope context_scope(context);
+      ExpectInt32("f()", 2);
+    }
+    {
+      v8::HandleScope handle_scope(isolate);
+      v8::Local<v8::Context> context =
+          v8::Context::New(isolate, no_extension, no_template, no_object, 2);
+      v8::Context::Scope context_scope(context);
+      ExpectUndefined("this.f");
+    }
+  }
+
+  isolate->Dispose();
+  delete[] blob.data;
+}
+
 TEST(SerializationMemoryStats) {
   FLAG_profile_deserialization = true;
   FLAG_always_opt = false;

test/memory/Memory.json

@@ -12,7 +12,7 @@
     },
     {
       "name": "ReservedMemoryContext",
-      "results_regexp": "(\\d+) bytes per context$"
+      "results_regexp": "(\\d+) bytes per context #0$"
     },
     {
       "name": "SnapshotSizeStartup",
@@ -20,7 +20,7 @@
     },
     {
       "name": "SnapshotSizeContext",
-      "results_regexp": "(\\d+) bytes for context$"
+      "results_regexp": "(\\d+) bytes for context #0$"
     }
   ]
 }