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 #include "base/logging.h"
   9 #include "base/threading/thread_checker_impl.h"
  10
  11 // Apart from debug builds, we also enable the thread checker in
  12 // builds with DCHECK_ALWAYS_ON so that trybots and waterfall bots
  13 // with this define will get the same level of thread checking as
  14 // debug bots.
  15 #if DCHECK_IS_ON()
  16 #define ENABLE_THREAD_CHECKER 1
  17 #else
  18 #define ENABLE_THREAD_CHECKER 0
  19 #endif
  20
  21 namespace base {
  22
  23 // Do nothing implementation, for use in release mode.
  24 //
  25 // Note: You should almost always use the ThreadChecker class to get the
  26 // right version for your build configuration.
  27 class ThreadCheckerDoNothing {
  28  public:
  29   bool CalledOnValidThread() const WARN_UNUSED_RESULT {
  30     return true;
  31   }
  32
  33   void DetachFromThread() {}
  34 };
  35
  36 // ThreadChecker is a helper class used to help verify that some methods of a
  37 // class are called from the same thread. It provides identical functionality to
  38 // base::NonThreadSafe, but it is meant to be held as a member variable, rather
  39 // than inherited from base::NonThreadSafe.
  40 //
  41 // While inheriting from base::NonThreadSafe may give a clear indication about
  42 // the thread-safety of a class, it may also lead to violations of the style
  43 // guide with regard to multiple inheritance. The choice between having a
  44 // ThreadChecker member and inheriting from base::NonThreadSafe should be based
  45 // on whether:
  46 //  - Derived classes need to know the thread they belong to, as opposed to
  47 //    having that functionality fully encapsulated in the base class.
  48 //  - Derived classes should be able to reassign the base class to another
  49 //    thread, via DetachFromThread.
  50 //
  51 // If neither of these are true, then having a ThreadChecker member and calling
  52 // CalledOnValidThread is the preferable solution.
  53 //
  54 // Example:
  55 // class MyClass {
  56 //  public:
  57 //   void Foo() {
  58 //     DCHECK(thread_checker_.CalledOnValidThread());
  59 //     ... (do stuff) ...
  60 //   }
  61 //
  62 //  private:
  63 //   ThreadChecker thread_checker_;
  64 // }
  65 //
  66 // In Release mode, CalledOnValidThread will always return true.
  67 #if ENABLE_THREAD_CHECKER
  68 class ThreadChecker : public ThreadCheckerImpl {
  69 };
  70 #else
  71 class ThreadChecker : public ThreadCheckerDoNothing {
  72 };
  73 #endif  // ENABLE_THREAD_CHECKER
  74
  75 #undef ENABLE_THREAD_CHECKER
  76
  77 }  // namespace base
  78
  79 #endif  // BASE_THREADING_THREAD_CHECKER_H_