[serializer] Add API to warm up startup snapshot with an additional script.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 647bd6e21bca049e94c62ce8cea89a8605acbe71..f933540ba3b1698528c7fee65b3aaa6941c6057c 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -341,12 +341,23 @@ void V8::SetSnapshotDataBlob(StartupData* snapshot_blob) {
   i::V8::SetSnapshotBlob(snapshot_blob);
 }
 
+namespace {
+
+class ArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
+ public:
+  virtual void* Allocate(size_t length) {
+    void* data = AllocateUninitialized(length);
+    return data == NULL ? data : memset(data, 0, length);
+  }
+  virtual void* AllocateUninitialized(size_t length) { return malloc(length); }
+  virtual void Free(void* data, size_t) { free(data); }
+};
 
 bool RunExtraCode(Isolate* isolate, Local<Context> context,
-                  const char* utf8_source) {
-  // Run custom script if provided.
+                  const char* utf8_source, const char* name) {
   base::ElapsedTimer timer;
   timer.Start();
+  Context::Scope context_scope(context);
   TryCatch try_catch(isolate);
   Local<String> source_string;
   if (!String::NewFromUtf8(isolate, utf8_source, NewStringType::kNormal)
@@ -354,7 +365,7 @@ bool RunExtraCode(Isolate* isolate, Local<Context> context,
     return false;
   }
   Local<String> resource_name =
-      String::NewFromUtf8(isolate, "<embedded script>", NewStringType::kNormal)
+      String::NewFromUtf8(isolate, name, NewStringType::kNormal)
           .ToLocalChecked();
   ScriptOrigin origin(resource_name);
   ScriptCompiler::Source source(source_string, origin);
@@ -362,7 +373,7 @@ bool RunExtraCode(Isolate* isolate, Local<Context> context,
   if (!ScriptCompiler::Compile(context, &source).ToLocal(&script)) return false;
   if (script->Run(context).IsEmpty()) return false;
   if (i::FLAG_profile_deserialization) {
-    i::PrintF("Executing custom snapshot script took %0.3f ms\n",
+    i::PrintF("Executing custom snapshot script %s took %0.3f ms\n", name,
               timer.Elapsed().InMillisecondsF());
   }
   timer.Stop();
@@ -370,92 +381,148 @@ bool RunExtraCode(Isolate* isolate, Local<Context> context,
   return true;
 }
 
+StartupData SerializeIsolateAndContext(
+    Isolate* isolate, Persistent<Context>* context,
+    i::Snapshot::Metadata metadata,
+    i::StartupSerializer::FunctionCodeHandling function_code_handling) {
+  if (context->IsEmpty()) return {NULL, 0};
 
-namespace {
+  i::Isolate* internal_isolate = reinterpret_cast<i::Isolate*>(isolate);
 
-class ArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
- public:
-  virtual void* Allocate(size_t length) {
-    void* data = AllocateUninitialized(length);
-    return data == NULL ? data : memset(data, 0, length);
+  // If we don't do this then we end up with a stray root pointing at the
+  // context even after we have disposed of the context.
+  internal_isolate->heap()->CollectAllAvailableGarbage("mksnapshot");
+
+  // GC may have cleared weak cells, so compact any WeakFixedArrays
+  // found on the heap.
+  i::HeapIterator iterator(internal_isolate->heap(),
+                           i::HeapIterator::kFilterUnreachable);
+  for (i::HeapObject* o = iterator.next(); o != NULL; o = iterator.next()) {
+    if (o->IsPrototypeInfo()) {
+      i::Object* prototype_users = i::PrototypeInfo::cast(o)->prototype_users();
+      if (prototype_users->IsWeakFixedArray()) {
+        i::WeakFixedArray* array = i::WeakFixedArray::cast(prototype_users);
+        array->Compact<i::JSObject::PrototypeRegistryCompactionCallback>();
+      }
+    } else if (o->IsScript()) {
+      i::Object* shared_list = i::Script::cast(o)->shared_function_infos();
+      if (shared_list->IsWeakFixedArray()) {
+        i::WeakFixedArray* array = i::WeakFixedArray::cast(shared_list);
+        array->Compact<i::WeakFixedArray::NullCallback>();
+      }
+    }
   }
-  virtual void* AllocateUninitialized(size_t length) { return malloc(length); }
-  virtual void Free(void* data, size_t) { free(data); }
-};
+
+  i::Object* raw_context = *v8::Utils::OpenPersistent(*context);
+  context->Reset();
+
+  i::SnapshotByteSink snapshot_sink;
+  i::StartupSerializer ser(internal_isolate, &snapshot_sink,
+                           function_code_handling);
+  ser.SerializeStrongReferences();
+
+  i::SnapshotByteSink context_sink;
+  i::PartialSerializer context_ser(internal_isolate, &ser, &context_sink);
+  context_ser.Serialize(&raw_context);
+  ser.SerializeWeakReferencesAndDeferred();
+
+  return i::Snapshot::CreateSnapshotBlob(ser, context_ser, metadata);
+}
 
 }  // namespace
 
+StartupData V8::CreateSnapshotDataBlob(const char* embedded_source) {
+  // Create a new isolate and a new context from scratch, optionally run
+  // a script to embed, and serialize to create a snapshot blob.
+  StartupData result = {NULL, 0};
+
+  base::ElapsedTimer timer;
+  timer.Start();
 
-StartupData V8::CreateSnapshotDataBlob(const char* custom_source) {
-  i::Isolate* internal_isolate = new i::Isolate(true);
   ArrayBufferAllocator allocator;
+  i::Isolate* internal_isolate = new i::Isolate(true);
   internal_isolate->set_array_buffer_allocator(&allocator);
   Isolate* isolate = reinterpret_cast<Isolate*>(internal_isolate);
-  StartupData result = {NULL, 0};
+
   {
-    base::ElapsedTimer timer;
-    timer.Start();
     Isolate::Scope isolate_scope(isolate);
     internal_isolate->Init(NULL);
     Persistent<Context> context;
-    i::Snapshot::Metadata metadata;
     {
       HandleScope handle_scope(isolate);
       Local<Context> new_context = Context::New(isolate);
       context.Reset(isolate, new_context);
-      if (custom_source != NULL) {
-        metadata.set_embeds_script(true);
-        Context::Scope context_scope(new_context);
-        if (!RunExtraCode(isolate, new_context, custom_source)) context.Reset();
+      if (embedded_source != NULL &&
+          !RunExtraCode(isolate, new_context, embedded_source, "<embedded>")) {
+        context.Reset();
       }
     }
-    if (!context.IsEmpty()) {
-      // If we don't do this then we end up with a stray root pointing at the
-      // context even after we have disposed of the context.
-      internal_isolate->heap()->CollectAllAvailableGarbage("mksnapshot");
-
-      // GC may have cleared weak cells, so compact any WeakFixedArrays
-      // found on the heap.
-      i::HeapIterator iterator(internal_isolate->heap(),
-                               i::HeapIterator::kFilterUnreachable);
-      for (i::HeapObject* o = iterator.next(); o != NULL; o = iterator.next()) {
-        if (o->IsPrototypeInfo()) {
-          i::Object* prototype_users =
-              i::PrototypeInfo::cast(o)->prototype_users();
-          if (prototype_users->IsWeakFixedArray()) {
-            i::WeakFixedArray* array = i::WeakFixedArray::cast(prototype_users);
-            array->Compact<i::JSObject::PrototypeRegistryCompactionCallback>();
-          }
-        } else if (o->IsScript()) {
-          i::Object* shared_list = i::Script::cast(o)->shared_function_infos();
-          if (shared_list->IsWeakFixedArray()) {
-            i::WeakFixedArray* array = i::WeakFixedArray::cast(shared_list);
-            array->Compact<i::WeakFixedArray::NullCallback>();
-          }
-        }
-      }
 
-      i::Object* raw_context = *v8::Utils::OpenPersistent(context);
-      context.Reset();
+    i::Snapshot::Metadata metadata;
+    metadata.set_embeds_script(embedded_source != NULL);
 
-      i::SnapshotByteSink snapshot_sink;
-      i::StartupSerializer ser(internal_isolate, &snapshot_sink);
-      ser.SerializeStrongReferences();
+    result = SerializeIsolateAndContext(
+        isolate, &context, metadata, i::StartupSerializer::CLEAR_FUNCTION_CODE);
+    DCHECK(context.IsEmpty());
+  }
+  isolate->Dispose();
 
-      i::SnapshotByteSink context_sink;
-      i::PartialSerializer context_ser(internal_isolate, &ser, &context_sink);
-      context_ser.Serialize(&raw_context);
-      ser.SerializeWeakReferencesAndDeferred();
+  if (i::FLAG_profile_deserialization) {
+    i::PrintF("Creating snapshot took %0.3f ms\n",
+              timer.Elapsed().InMillisecondsF());
+  }
+  timer.Stop();
+  return result;
+}
 
-      result = i::Snapshot::CreateSnapshotBlob(ser, context_ser, metadata);
-    }
-    if (i::FLAG_profile_deserialization) {
-      i::PrintF("Creating snapshot took %0.3f ms\n",
-                timer.Elapsed().InMillisecondsF());
+StartupData V8::WarmUpSnapshotDataBlob(StartupData cold_snapshot_blob,
+                                       const char* warmup_source) {
+  CHECK(cold_snapshot_blob.raw_size > 0 && cold_snapshot_blob.data != NULL);
+  CHECK(warmup_source != NULL);
+  // Use following steps to create a warmed up snapshot blob from a cold one:
+  //  - Create a new isolate from the cold snapshot.
+  //  - Create a new context to run the warmup script. This will trigger
+  //    compilation of executed functions.
+  //  - Create a new context. This context will be unpolluted.
+  //  - Serialize the isolate and the second context into a new snapshot blob.
+  StartupData result = {NULL, 0};
+
+  base::ElapsedTimer timer;
+  timer.Start();
+
+  ArrayBufferAllocator allocator;
+  i::Isolate* internal_isolate = new i::Isolate(true);
+  internal_isolate->set_array_buffer_allocator(&allocator);
+  internal_isolate->set_snapshot_blob(&cold_snapshot_blob);
+  Isolate* isolate = reinterpret_cast<Isolate*>(internal_isolate);
+
+  {
+    Isolate::Scope isolate_scope(isolate);
+    i::Snapshot::Initialize(internal_isolate);
+    Persistent<Context> context;
+    {
+      HandleScope handle_scope(isolate);
+      Local<Context> warmup_context = Context::New(isolate);
+      if (RunExtraCode(isolate, warmup_context, warmup_source, "<warm-up>")) {
+        Local<Context> fresh_context = Context::New(isolate);
+        context.Reset(isolate, fresh_context);
+      }
     }
-    timer.Stop();
+
+    i::Snapshot::Metadata metadata;
+    metadata.set_embeds_script(i::Snapshot::EmbedsScript(internal_isolate));
+
+    result = SerializeIsolateAndContext(
+        isolate, &context, metadata, i::StartupSerializer::KEEP_FUNCTION_CODE);
+    DCHECK(context.IsEmpty());
   }
   isolate->Dispose();
+
+  if (i::FLAG_profile_deserialization) {
+    i::PrintF("Warming up snapshot took %0.3f ms\n",
+              timer.Elapsed().InMillisecondsF());
+  }
+  timer.Stop();
   return result;
 }