base/threading/non_thread_safe.h

   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.
   4
   5 #ifndef BASE_THREADING_NON_THREAD_SAFE_H_
   6 #define BASE_THREADING_NON_THREAD_SAFE_H_
   7
   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"
  13
  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
  20
  21 #if ENABLE_NON_THREAD_SAFE
  22 #include "base/threading/non_thread_safe_impl.h"
  23 #endif
  24
  25 namespace base {
  26
  27 // Do nothing implementation of NonThreadSafe, for release mode.
  28 //
  29 // Note: You should almost always use the NonThreadSafe class to get
  30 // the right version of the class for your build configuration.
  31 class NonThreadSafeDoNothing {
  32  public:
  33   bool CalledOnValidThread() const {
  34     return true;
  35   }
  36
  37  protected:
  38   ~NonThreadSafeDoNothing() {}
  39   void DetachFromThread() {}
  40 };
  41
  42 // NonThreadSafe is a helper class used to help verify that methods of a
  43 // class are called from the same thread.  One can inherit from this class
  44 // and use CalledOnValidThread() to verify.
  45 //
  46 // This is intended to be used with classes that appear to be thread safe, but
  47 // aren't.  For example, a service or a singleton like the preferences system.
  48 //
  49 // Example:
  50 // class MyClass : public base::NonThreadSafe {
  51 //  public:
  52 //   void Foo() {
  53 //     DCHECK(CalledOnValidThread());
  54 //     ... (do stuff) ...
  55 //   }
  56 // }
  57 //
  58 // Note that base::ThreadChecker offers identical functionality to
  59 // NonThreadSafe, but does not require inheritence. In general, it is preferable
  60 // to have a base::ThreadChecker as a member, rather than inherit from
  61 // NonThreadSafe. For more details about when to choose one over the other, see
  62 // the documentation for base::ThreadChecker.
  63 #if ENABLE_NON_THREAD_SAFE
  64 typedef NonThreadSafeImpl NonThreadSafe;
  65 #else
  66 typedef NonThreadSafeDoNothing NonThreadSafe;
  67 #endif  // ENABLE_NON_THREAD_SAFE
  68
  69 #undef ENABLE_NON_THREAD_SAFE
  70
  71 }  // namespace base
  72
  73 #endif  // BASE_NON_THREAD_SAFE_H_