1 files changed, 34 insertions, 0 deletions
diff --git a/security/sandbox/chromium/base/memory/singleton.cc b/security/sandbox/chromium/base/memory/singleton.cc
new file mode 100644
index 000000000..f68ecaa8d
--- /dev/null
+++ b/security/sandbox/chromium/base/memory/singleton.cc
@@ -0,0 +1,34 @@
+// Copyright (c) 2011 The Chromium 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 "base/memory/singleton.h"
+#include "base/threading/platform_thread.h"
+
+namespace base {
+namespace internal {
+
+subtle::AtomicWord WaitForInstance(subtle::AtomicWord* instance) {
+  // Handle the race. Another thread beat us and either:
+  // - Has the object in BeingCreated state
+  // - Already has the object created...
+  // We know value != NULL.  It could be kBeingCreatedMarker, or a valid ptr.
+  // Unless your constructor can be very time consuming, it is very unlikely
+  // to hit this race.  When it does, we just spin and yield the thread until
+  // the object has been created.
+  subtle::AtomicWord value;
+  while (true) {
+    // The load has acquire memory ordering as the thread which reads the
+    // instance pointer must acquire visibility over the associated data.
+    // The pairing Release_Store operation is in Singleton::get().
+    value = subtle::Acquire_Load(instance);
+    if (value != kBeingCreatedMarker)
+      break;
+    PlatformThread::YieldCurrentThread();
+  }
+  return value;
+}
+
+}  // namespace internal
+}  // namespace base
+