michael@0: // Copyright (c) 2012 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: #ifndef BASE_SEQUENCED_TASK_RUNNER_HELPERS_H_
michael@0: #define BASE_SEQUENCED_TASK_RUNNER_HELPERS_H_
michael@0: 
michael@0: #include "base/basictypes.h"
michael@0: 
michael@0: // TODO(akalin): Investigate whether it's possible to just have
michael@0: // SequencedTaskRunner use these helpers (instead of MessageLoop).
michael@0: // Then we can just move these to sequenced_task_runner.h.
michael@0: 
michael@0: namespace tracked_objects {
michael@0: class Location;
michael@0: }
michael@0: 
michael@0: namespace base {
michael@0: 
michael@0: namespace subtle {
michael@0: template <class T, class R> class DeleteHelperInternal;
michael@0: template <class T, class R> class ReleaseHelperInternal;
michael@0: }
michael@0: 
michael@0: // Template helpers which use function indirection to erase T from the
michael@0: // function signature while still remembering it so we can call the
michael@0: // correct destructor/release function.
michael@0: //
michael@0: // We use this trick so we don't need to include bind.h in a header
michael@0: // file like sequenced_task_runner.h. We also wrap the helpers in a
michael@0: // templated class to make it easier for users of DeleteSoon to
michael@0: // declare the helper as a friend.
michael@0: template <class T>
michael@0: class DeleteHelper {
michael@0:  private:
michael@0:   template <class T2, class R> friend class subtle::DeleteHelperInternal;
michael@0: 
michael@0:   static void DoDelete(const void* object) {
michael@0:     delete reinterpret_cast<const T*>(object);
michael@0:   }
michael@0: 
michael@0:   DISALLOW_COPY_AND_ASSIGN(DeleteHelper);
michael@0: };
michael@0: 
michael@0: template <class T>
michael@0: class ReleaseHelper {
michael@0:  private:
michael@0:   template <class T2, class R> friend class subtle::ReleaseHelperInternal;
michael@0: 
michael@0:   static void DoRelease(const void* object) {
michael@0:     reinterpret_cast<const T*>(object)->Release();
michael@0:   }
michael@0: 
michael@0:   DISALLOW_COPY_AND_ASSIGN(ReleaseHelper);
michael@0: };
michael@0: 
michael@0: namespace subtle {
michael@0: 
michael@0: // An internal SequencedTaskRunner-like class helper for DeleteHelper
michael@0: // and ReleaseHelper.  We don't want to expose the Do*() functions
michael@0: // directly directly since the void* argument makes it possible to
michael@0: // pass/ an object of the wrong type to delete.  Instead, we force
michael@0: // callers to go through these internal helpers for type
michael@0: // safety. SequencedTaskRunner-like classes which expose DeleteSoon or
michael@0: // ReleaseSoon methods should friend the appropriate helper and
michael@0: // implement a corresponding *Internal method with the following
michael@0: // signature:
michael@0: //
michael@0: // bool(const tracked_objects::Location&,
michael@0: //      void(*function)(const void*),
michael@0: //      void* object)
michael@0: //
michael@0: // An implementation of this function should simply create a
michael@0: // base::Closure from (function, object) and return the result of
michael@0: // posting the task.
michael@0: template <class T, class ReturnType>
michael@0: class DeleteHelperInternal {
michael@0:  public:
michael@0:   template <class SequencedTaskRunnerType>
michael@0:   static ReturnType DeleteViaSequencedTaskRunner(
michael@0:       SequencedTaskRunnerType* sequenced_task_runner,
michael@0:       const tracked_objects::Location& from_here,
michael@0:       const T* object) {
michael@0:     return sequenced_task_runner->DeleteSoonInternal(
michael@0:         from_here, &DeleteHelper<T>::DoDelete, object);
michael@0:   }
michael@0: 
michael@0:  private:
michael@0:   DISALLOW_COPY_AND_ASSIGN(DeleteHelperInternal);
michael@0: };
michael@0: 
michael@0: template <class T, class ReturnType>
michael@0: class ReleaseHelperInternal {
michael@0:  public:
michael@0:   template <class SequencedTaskRunnerType>
michael@0:   static ReturnType ReleaseViaSequencedTaskRunner(
michael@0:       SequencedTaskRunnerType* sequenced_task_runner,
michael@0:       const tracked_objects::Location& from_here,
michael@0:       const T* object) {
michael@0:     return sequenced_task_runner->ReleaseSoonInternal(
michael@0:         from_here, &ReleaseHelper<T>::DoRelease, object);
michael@0:   }
michael@0: 
michael@0:  private:
michael@0:   DISALLOW_COPY_AND_ASSIGN(ReleaseHelperInternal);
michael@0: };
michael@0: 
michael@0: }  // namespace subtle
michael@0: 
michael@0: }  // namespace base
michael@0: 
michael@0: #endif  // BASE_SEQUENCED_TASK_RUNNER_HELPERS_H_