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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_MESSAGE_LOOP_HELPERS_H_
#define BASE_MESSAGE_LOOP_HELPERS_H_
#pragma once
#include "base/basictypes.h"
namespace tracked_objects {
class Location;
}
namespace base {
namespace subtle {
template <class T, class R> class DeleteHelperInternal;
template <class T, class R> class ReleaseHelperInternal;
}
// Template helpers which use a function indirection to erase T from the
// function signature while still remembering it so we can call the correct
// destructor/release function.
// We use this trick so we don't need to include bind.h in a header file like
// message_loop.h. We also wrap the helpers in a templated class to make it
// easier for users of DeleteSoon to declare the helper as a friend.
template <class T>
class DeleteHelper {
private:
template <class T2, class R> friend class subtle::DeleteHelperInternal;
static void DoDelete(const void* object) {
delete reinterpret_cast<const T*>(object);
}
DISALLOW_COPY_AND_ASSIGN(DeleteHelper);
};
template <class T>
class ReleaseHelper {
private:
template <class T2, class R> friend class subtle::ReleaseHelperInternal;
static void DoRelease(const void* object) {
reinterpret_cast<const T*>(object)->Release();
}
DISALLOW_COPY_AND_ASSIGN(ReleaseHelper);
};
namespace subtle {
// An internal MessageLoop-like class helper for DeleteHelper and ReleaseHelper.
// We don't want to expose the Do*() functions directly directly since the void*
// argument makes it possible to pass/ an object of the wrong type to delete.
// Instead, we force callers to go through these internal helpers for type
// safety. MessageLoop-like classes which expose DeleteSoon or ReleaseSoon
// methods should friend the appropriate helper and implement a corresponding
// *Internal method with the following signature:
// bool(const tracked_objects::Location&,
// void(*function)(const void*),
// void* object)
// An implementation of this function should simply create a base::Closure
// from (function, object) and return the result of posting the task.
template <class T, class ReturnType>
class DeleteHelperInternal {
public:
template <class MessageLoopType>
static ReturnType DeleteOnMessageLoop(
MessageLoopType* message_loop,
const tracked_objects::Location& from_here,
const T* object) {
return message_loop->DeleteSoonInternal(from_here,
&DeleteHelper<T>::DoDelete,
object);
}
private:
DISALLOW_COPY_AND_ASSIGN(DeleteHelperInternal);
};
template <class T, class ReturnType>
class ReleaseHelperInternal {
public:
template <class MessageLoopType>
static ReturnType ReleaseOnMessageLoop(
MessageLoopType* message_loop,
const tracked_objects::Location& from_here,
const T* object) {
return message_loop->ReleaseSoonInternal(from_here,
&ReleaseHelper<T>::DoRelease,
object);
}
private:
DISALLOW_COPY_AND_ASSIGN(ReleaseHelperInternal);
};
} // namespace subtle
} // namespace base
#endif // BASE_MESSAGE_LOOP_HELPERS_H_
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