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1 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #include "base/threading/thread_collision_warner.h"
6 
7 #include "base/logging.h"
8 #include "base/threading/platform_thread.h"
9 
10 namespace base {
11 
warn()12 void DCheckAsserter::warn() {
13   NOTREACHED() << "Thread Collision";
14 }
15 
CurrentThread()16 static subtle::Atomic32 CurrentThread() {
17   const PlatformThreadId current_thread_id = PlatformThread::CurrentId();
18   // We need to get the thread id into an atomic data type. This might be a
19   // truncating conversion, but any loss-of-information just increases the
20   // chance of a fault negative, not a false positive.
21   const subtle::Atomic32 atomic_thread_id =
22       static_cast<subtle::Atomic32>(current_thread_id);
23 
24   return atomic_thread_id;
25 }
26 
EnterSelf()27 void ThreadCollisionWarner::EnterSelf() {
28   // If the active thread is 0 then I'll write the current thread ID
29   // if two or more threads arrive here only one will succeed to
30   // write on valid_thread_id_ the current thread ID.
31   subtle::Atomic32 current_thread_id = CurrentThread();
32 
33   int previous_value = subtle::NoBarrier_CompareAndSwap(&valid_thread_id_,
34                                                         0,
35                                                         current_thread_id);
36   if (previous_value != 0 && previous_value != current_thread_id) {
37     // gotcha! a thread is trying to use the same class and that is
38     // not current thread.
39     asserter_->warn();
40   }
41 
42   subtle::NoBarrier_AtomicIncrement(&counter_, 1);
43 }
44 
Enter()45 void ThreadCollisionWarner::Enter() {
46   subtle::Atomic32 current_thread_id = CurrentThread();
47 
48   if (subtle::NoBarrier_CompareAndSwap(&valid_thread_id_,
49                                        0,
50                                        current_thread_id) != 0) {
51     // gotcha! another thread is trying to use the same class.
52     asserter_->warn();
53   }
54 
55   subtle::NoBarrier_AtomicIncrement(&counter_, 1);
56 }
57 
Leave()58 void ThreadCollisionWarner::Leave() {
59   if (subtle::Barrier_AtomicIncrement(&counter_, -1) == 0) {
60     subtle::NoBarrier_Store(&valid_thread_id_, 0);
61   }
62 }
63 
64 }  // namespace base
65