Protect access to the external_snapshot_blob global with a lock.

src/snapshot-external.cc

 // Copyright 2006-2008 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.
 
 // Used for building with external snapshots.
 
 #include "src/snapshot.h"
 
+#include "src/base/platform/mutex.h"
 #include "src/serialize.h"
 #include "src/snapshot-source-sink.h"
 #include "src/v8.h"  // for V8::Initialize
 
 
 #ifndef V8_USE_EXTERNAL_STARTUP_DATA
 #error snapshot-external.cc is used only for the external snapshot build.
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
 
 
 namespace v8 {
 namespace internal {
 
+static base::LazyMutex external_startup_data_mutex = LAZY_MUTEX_INITIALIZER;
 static v8::StartupData external_startup_blob = {NULL, 0};
 
 void SetSnapshotFromFile(StartupData* snapshot_blob) {
+  base::LockGuard<base::Mutex> lock_guard(
+      external_startup_data_mutex.Pointer());
   DCHECK(snapshot_blob);
   DCHECK(snapshot_blob->data);
   DCHECK(snapshot_blob->raw_size > 0);
   DCHECK(!external_startup_blob.data);
   DCHECK(Snapshot::SnapshotIsValid(snapshot_blob));
   external_startup_blob = *snapshot_blob;
 }
 
 
-const v8::StartupData Snapshot::SnapshotBlob() { return external_startup_blob; }
+const v8::StartupData Snapshot::SnapshotBlob() {
+  base::LockGuard<base::Mutex> lock_guard(
+      external_startup_data_mutex.Pointer());
+  return external_startup_blob;
+}
 } }  // namespace v8::internal