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
10namespace base {
11
12void DCheckAsserter::warn() {
13  NOTREACHED() << "Thread Collision";
14}
15
16static 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
27void 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
45void 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
58void 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