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authorMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
committerMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
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Add m-esr52 at 52.6.0
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diff --git a/security/sandbox/chromium/base/memory/singleton.cc b/security/sandbox/chromium/base/memory/singleton.cc
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+// 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
+