base/sequence_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_SEQUENCE_CHECKER_H_
   6 #define BASE_SEQUENCE_CHECKER_H_
   7
   8 #include "base/memory/ref_counted.h"
   9
  10 // See comments for the similar block in thread_checker.h.
  11 #if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
  12 #define ENABLE_SEQUENCE_CHECKER 1
  13 #else
  14 #define ENABLE_SEQUENCE_CHECKER 0
  15 #endif
  16
  17 #if ENABLE_SEQUENCE_CHECKER
  18 #include "base/sequence_checker_impl.h"
  19 #endif
  20
  21 namespace base {
  22
  23 class SequencedTaskRunner;
  24
  25 // Do nothing implementation, for use in release mode.
  26 //
  27 // Note: You should almost always use the SequenceChecker class to get
  28 // the right version for your build configuration.
  29 class SequenceCheckerDoNothing {
  30  public:
  31   bool CalledOnValidSequence() const {
  32     return true;
  33   }
  34
  35   void ChangeSequence(
  36       const scoped_refptr<SequencedTaskRunner>& sequenced_task_runner) {}
  37 };
  38
  39 // SequenceChecker is a helper class used to help verify that some
  40 // methods of a class are called in sequence -- that is, called from
  41 // the same SequencedTaskRunner. It is a generalization of
  42 // ThreadChecker; see comments in sequence_checker_impl.h for details.
  43 //
  44 // Example:
  45 // class MyClass {
  46 //  public:
  47 //   explicit MyClass(
  48 //       const scoped_refptr<SequencedTaskRunner>& sequenced_task_runner)
  49 //       : sequence_checker_(sequenced_task_runner) {}
  50 //
  51 //   void Foo() {
  52 //     DCHECK(sequence_checker_.CalledOnValidSequence());
  53 //     ... (do stuff) ...
  54 //   }
  55 //
  56 //  private:
  57 //   SequenceChecker sequence_checker_;
  58 // }
  59 //
  60 // In Release mode, CalledOnValidSequence will always return true.
  61 #if ENABLE_SEQUENCE_CHECKER
  62 class SequenceChecker : public SequenceCheckerImpl {
  63  public:
  64   explicit SequenceChecker(
  65       const scoped_refptr<SequencedTaskRunner>& sequenced_task_runner)
  66       : SequenceCheckerImpl(sequenced_task_runner) {}
  67 };
  68 #else
  69 class SequenceChecker : public SequenceCheckerDoNothing {
  70  public:
  71   explicit SequenceChecker(
  72       const scoped_refptr<SequencedTaskRunner>& sequenced_task_runner) {}
  73 };
  74 #endif  // ENABLE_SEQUENCE_CHECKER
  75
  76 #undef ENABLE_SEQUENCE_CHECKER
  77
  78 }  // namespace base
  79
  80 #endif  // BASE_SEQUENCE_CHECKER_H_