Protect access to the external_snapshot_blob global with a lock.

src/snapshot-external.cc

Index: src/snapshot-external.cc
diff --git a/src/snapshot-external.cc b/src/snapshot-external.cc
index f26a5a1c18dba7a2b43410e352778a1bf179d4b5..a9a5df1cd7c2a04f2c40a760c79ffb89a2b3742a 100644
--- a/src/snapshot-external.cc
+++ b/src/snapshot-external.cc
@@ -6,6 +6,7 @@
 
 #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
@@ -19,9 +20,12 @@
 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);
@@ -31,5 +35,9 @@ void SetSnapshotFromFile(StartupData* 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