SnapshotCreator: start from existing snapshot if we have one

src/api.cc

 // Copyright 2012 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/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 497 matching lines @@
   Isolate* isolate = reinterpret_cast<Isolate*>(internal_isolate);
   SnapshotCreatorData* data = new SnapshotCreatorData(isolate);
   data->isolate_ = isolate;
   internal_isolate->set_array_buffer_allocator(&data->allocator_);
   internal_isolate->set_api_external_references(external_references);
   isolate->Enter();
   if (existing_snapshot) {
     internal_isolate->set_snapshot_blob(existing_snapshot);
     i::Snapshot::Initialize(internal_isolate);
   } else {
-    internal_isolate->Init(nullptr);
+    // If we have a snapshot, use it for bootstrapping; otherwise start
+    // from scratch.
+    const StartupData* snapshot_blob = i::Snapshot::DefaultSnapshotBlob();

[Yang, 2017/03/07 11:28:11]

We could also make this the default parameter for existing_snapshot?

[Jakob Kummerow, 2017/03/07 12:39:15]

Done.

+    if (snapshot_blob != nullptr && snapshot_blob->raw_size > 0) {
+      internal_isolate->set_snapshot_blob(snapshot_blob);
+      i::Snapshot::Initialize(internal_isolate);
+    } else {
+      internal_isolate->Init(nullptr);
+    }
   }
   data_ = data;
 }
 
 SnapshotCreator::~SnapshotCreator() {
   SnapshotCreatorData* data = SnapshotCreatorData::cast(data_);
   DCHECK(data->created_);
   Isolate* isolate = data->isolate_;
   isolate->Exit();
   isolate->Dispose();
@@ skipping 9728 matching lines @@
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 }  // namespace internal
 }  // namespace v8