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diff --git a/base/threading/thread_collision_warner.cc b/base/threading/thread_collision_warner.cc
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+++ b/base/threading/thread_collision_warner.cc
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+// Copyright (c) 2010 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/threading/thread_collision_warner.h"
+
+#include "base/logging.h"
+#include "base/threading/platform_thread.h"
+
+namespace base {
+
+void DCheckAsserter::warn() {
+ NOTREACHED() << "Thread Collision";
+}
+
+static subtle::Atomic32 CurrentThread() {
+ const PlatformThreadId current_thread_id = PlatformThread::CurrentId();
+ // We need to get the thread id into an atomic data type. This might be a
+ // truncating conversion, but any loss-of-information just increases the
+ // chance of a fault negative, not a false positive.
+ const subtle::Atomic32 atomic_thread_id =
+ static_cast<subtle::Atomic32>(current_thread_id);
+
+ return atomic_thread_id;
+}
+
+void ThreadCollisionWarner::EnterSelf() {
+ // If the active thread is 0 then I'll write the current thread ID
+ // if two or more threads arrive here only one will succeed to
+ // write on valid_thread_id_ the current thread ID.
+ subtle::Atomic32 current_thread_id = CurrentThread();
+
+ int previous_value = subtle::NoBarrier_CompareAndSwap(&valid_thread_id_,
+ 0,
+ current_thread_id);
+ if (previous_value != 0 && previous_value != current_thread_id) {
+ // gotcha! a thread is trying to use the same class and that is
+ // not current thread.
+ asserter_->warn();
+ }
+
+ subtle::NoBarrier_AtomicIncrement(&counter_, 1);
+}
+
+void ThreadCollisionWarner::Enter() {
+ subtle::Atomic32 current_thread_id = CurrentThread();
+
+ if (subtle::NoBarrier_CompareAndSwap(&valid_thread_id_,
+ 0,
+ current_thread_id) != 0) {
+ // gotcha! another thread is trying to use the same class.
+ asserter_->warn();
+ }
+
+ subtle::NoBarrier_AtomicIncrement(&counter_, 1);
+}
+
+void ThreadCollisionWarner::Leave() {
+ if (subtle::Barrier_AtomicIncrement(&counter_, -1) == 0) {
+ subtle::NoBarrier_Store(&valid_thread_id_, 0);
+ }
+}
+
+} // namespace base