base/threading/thread_checker.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_THREAD_CHECKER_H_
   6 #define BASE_THREADING_THREAD_CHECKER_H_
   7
   8 // Apart from debug builds, we also enable the thread checker in
   9 // builds with DCHECK_ALWAYS_ON so that trybots and waterfall bots
  10 // with this define will get the same level of thread checking as
  11 // debug bots.
  12 //
  13 // Note that this does not perfectly match situations where DCHECK is
  14 // enabled.  For example a non-official release build may have
  15 // DCHECK_ALWAYS_ON undefined (and therefore ThreadChecker would be
  16 // disabled) but have DCHECKs enabled at runtime.
  17 #if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
  18 #define ENABLE_THREAD_CHECKER 1
  19 #else
  20 #define ENABLE_THREAD_CHECKER 0
  21 #endif
  22
  23 #if ENABLE_THREAD_CHECKER
  24 #include "base/threading/thread_checker_impl.h"
  25 #endif
  26
  27 namespace base {
  28
  29 // Do nothing implementation, for use in release mode.
  30 //
  31 // Note: You should almost always use the ThreadChecker class to get the
  32 // right version for your build configuration.
  33 class ThreadCheckerDoNothing {
  34  public:
  35   bool CalledOnValidThread() const {
  36     return true;
  37   }
  38
  39   void DetachFromThread() {}
  40 };
  41
  42 // ThreadChecker is a helper class used to help verify that some methods of a
  43 // class are called from the same thread. It provides identical functionality to
  44 // base::NonThreadSafe, but it is meant to be held as a member variable, rather
  45 // than inherited from base::NonThreadSafe.
  46 //
  47 // While inheriting from base::NonThreadSafe may give a clear indication about
  48 // the thread-safety of a class, it may also lead to violations of the style
  49 // guide with regard to multiple inheritence. The choice between having a
  50 // ThreadChecker member and inheriting from base::NonThreadSafe should be based
  51 // on whether:
  52 //  - Derived classes need to know the thread they belong to, as opposed to
  53 //    having that functionality fully encapsulated in the base class.
  54 //  - Derived classes should be able to reassign the base class to another
  55 //    thread, via DetachFromThread.
  56 //
  57 // If neither of these are true, then having a ThreadChecker member and calling
  58 // CalledOnValidThread is the preferable solution.
  59 //
  60 // Example:
  61 // class MyClass {
  62 //  public:
  63 //   void Foo() {
  64 //     DCHECK(thread_checker_.CalledOnValidThread());
  65 //     ... (do stuff) ...
  66 //   }
  67 //
  68 //  private:
  69 //   ThreadChecker thread_checker_;
  70 // }
  71 //
  72 // In Release mode, CalledOnValidThread will always return true.
  73 #if ENABLE_THREAD_CHECKER
  74 class ThreadChecker : public ThreadCheckerImpl {
  75 };
  76 #else
  77 class ThreadChecker : public ThreadCheckerDoNothing {
  78 };
  79 #endif  // ENABLE_THREAD_CHECKER
  80
  81 #undef ENABLE_THREAD_CHECKER
  82
  83 }  // namespace base
  84
  85 #endif  // BASE_THREADING_THREAD_CHECKER_H_