chrome_frame/scoped_initialization_manager.h

   1 // Copyright 2013 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 CHROME_FRAME_SCOPED_INITIALIZATION_MANAGER_H_
   6 #define CHROME_FRAME_SCOPED_INITIALIZATION_MANAGER_H_
   7
   8 #include "base/basictypes.h"
   9 #include "base/lazy_instance.h"
  10 #include "base/synchronization/lock.h"
  11
  12 namespace chrome_frame {
  13
  14 // A class intended to be instantiated on the stack in a dyanmically loaded
  15 // shared object to initialize and shutdown the object's dependencies. |Traits|
  16 // must be a type with two public static void(void) functions named Initialize
  17 // and Shutdown. Traits::Initialize will be invoked when the first instance of
  18 // this class is created and Traits::Shutdown will be invoked when the last one
  19 // is destroyed.
  20 template<class Traits>
  21 class ScopedInitializationManager {
  22  public:
  23   ScopedInitializationManager() { AddRef(); }
  24   ~ScopedInitializationManager() { Release(); }
  25
  26  private:
  27   static void AddRef() {
  28     base::AutoLock auto_lock(lock_.Get());
  29     DCHECK_LT(ref_count_, kuint32max);
  30     if (++ref_count_ == 1)
  31       Traits::Initialize();
  32   }
  33
  34   static void Release() {
  35     base::AutoLock auto_lock(lock_.Get());
  36     DCHECK_GT(ref_count_, 0U);
  37     if (--ref_count_ == 0)
  38       Traits::Shutdown();
  39   }
  40
  41   static base::LazyInstance<base::Lock>::Leaky lock_;
  42   static uint32 ref_count_;
  43   DISALLOW_COPY_AND_ASSIGN(ScopedInitializationManager);
  44 };
  45
  46 template<class Traits> base::LazyInstance<base::Lock>::Leaky
  47     ScopedInitializationManager<Traits>::lock_ = LAZY_INSTANCE_INITIALIZER;
  48
  49 template<class Traits> uint32
  50     ScopedInitializationManager<Traits>::ref_count_ = 0;
  51
  52 }  // namespace chrome_frame
  53
  54 #endif  // CHROME_FRAME_SCOPED_INITIALIZATION_MANAGER_H_