non_thread_safe.h 2.24 KB
Newer Older
gejun's avatar
gejun committed
1 2 3 4 5 6 7 8 9 10 11
// Copyright (c) 2012 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.

#ifndef BASE_THREADING_NON_THREAD_SAFE_H_
#define BASE_THREADING_NON_THREAD_SAFE_H_

// Classes deriving from NonThreadSafe may need to suppress MSVC warning 4275:
// non dll-interface class 'Bar' used as base for dll-interface class 'Foo'.
// There is a specific macro to do it: NON_EXPORTED_BASE(), defined in
// compiler_specific.h
12
#include "butil/compiler_specific.h"
gejun's avatar
gejun committed
13 14 15 16 17 18 19 20

// See comment at top of thread_checker.h
#if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
#define ENABLE_NON_THREAD_SAFE 1
#else
#define ENABLE_NON_THREAD_SAFE 0
#endif

21
#include "butil/threading/non_thread_safe_impl.h"
gejun's avatar
gejun committed
22

23
namespace butil {
gejun's avatar
gejun committed
24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

// Do nothing implementation of NonThreadSafe, for release mode.
//
// Note: You should almost always use the NonThreadSafe class to get
// the right version of the class for your build configuration.
class NonThreadSafeDoNothing {
 public:
  bool CalledOnValidThread() const {
    return true;
  }

 protected:
  ~NonThreadSafeDoNothing() {}
  void DetachFromThread() {}
};

// NonThreadSafe is a helper class used to help verify that methods of a
// class are called from the same thread.  One can inherit from this class
// and use CalledOnValidThread() to verify.
//
// This is intended to be used with classes that appear to be thread safe, but
// aren't.  For example, a service or a singleton like the preferences system.
//
// Example:
48
// class MyClass : public butil::NonThreadSafe {
gejun's avatar
gejun committed
49 50 51 52 53 54 55
//  public:
//   void Foo() {
//     DCHECK(CalledOnValidThread());
//     ... (do stuff) ...
//   }
// }
//
56
// Note that butil::ThreadChecker offers identical functionality to
gejun's avatar
gejun committed
57
// NonThreadSafe, but does not require inheritance. In general, it is preferable
58
// to have a butil::ThreadChecker as a member, rather than inherit from
gejun's avatar
gejun committed
59
// NonThreadSafe. For more details about when to choose one over the other, see
60
// the documentation for butil::ThreadChecker.
gejun's avatar
gejun committed
61 62 63 64 65 66 67 68
#if ENABLE_NON_THREAD_SAFE
typedef NonThreadSafeImpl NonThreadSafe;
#else
typedef NonThreadSafeDoNothing NonThreadSafe;
#endif  // ENABLE_NON_THREAD_SAFE

#undef ENABLE_NON_THREAD_SAFE

69
}  // namespace butil
gejun's avatar
gejun committed
70 71

#endif  // BASE_THREADING_NON_THREAD_SAFE_H_