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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.
      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_
     74