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[chromium-blink-merge.git] / base / threading / non_thread_safe.h
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1 // Copyright (c) 2012 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.
5 #ifndef BASE_THREADING_NON_THREAD_SAFE_H_
6 #define BASE_THREADING_NON_THREAD_SAFE_H_
8 // Classes deriving from NonThreadSafe may need to suppress MSVC warning 4275:
9 // non dll-interface class 'Bar' used as base for dll-interface class 'Foo'.
10 // There is a specific macro to do it: NON_EXPORTED_BASE(), defined in
11 // compiler_specific.h
12 #include "base/compiler_specific.h"
14 // See comment at top of thread_checker.h
15 #if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
16 #define ENABLE_NON_THREAD_SAFE 1
17 #else
18 #define ENABLE_NON_THREAD_SAFE 0
19 #endif
21 #include "base/threading/non_thread_safe_impl.h"
23 namespace base {
25 // Do nothing implementation of NonThreadSafe, for release mode.
27 // Note: You should almost always use the NonThreadSafe class to get
28 // the right version of the class for your build configuration.
29 class NonThreadSafeDoNothing {
30 public:
31 bool CalledOnValidThread() const {
32 return true;
35 protected:
36 ~NonThreadSafeDoNothing() {}
37 void DetachFromThread() {}
40 // NonThreadSafe is a helper class used to help verify that methods of a
41 // class are called from the same thread. One can inherit from this class
42 // and use CalledOnValidThread() to verify.
44 // This is intended to be used with classes that appear to be thread safe, but
45 // aren't. For example, a service or a singleton like the preferences system.
47 // Example:
48 // class MyClass : public base::NonThreadSafe {
49 // public:
50 // void Foo() {
51 // DCHECK(CalledOnValidThread());
52 // ... (do stuff) ...
53 // }
54 // }
56 // Note that base::ThreadChecker offers identical functionality to
57 // NonThreadSafe, but does not require inheritance. In general, it is preferable
58 // to have a base::ThreadChecker as a member, rather than inherit from
59 // NonThreadSafe. For more details about when to choose one over the other, see
60 // the documentation for base::ThreadChecker.
61 #if ENABLE_NON_THREAD_SAFE
62 typedef NonThreadSafeImpl NonThreadSafe;
63 #else
64 typedef NonThreadSafeDoNothing NonThreadSafe;
65 #endif // ENABLE_NON_THREAD_SAFE
67 #undef ENABLE_NON_THREAD_SAFE
69 } // namespace base
71 #endif // BASE_THREADING_NON_THREAD_SAFE_H_