Ichthyostega
685a9b84ee
Benefits - get rid of yet another pervasive Boost dependency - define additional more fine grained policies (move only, clonable)
133 lines
4 KiB
C++
133 lines
4 KiB
C++
/*
|
|
SINGLETON-REF.hpp - helper template providing singleton-like access for implementation code
|
|
|
|
Copyright (C) Lumiera.org
|
|
2008, Hermann Vosseler <Ichthyostega@web.de>
|
|
|
|
This program is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU General Public License as
|
|
published by the Free Software Foundation; either version 2 of
|
|
the License, or (at your option) any later version.
|
|
|
|
This program is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
GNU General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with this program; if not, write to the Free Software
|
|
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
|
|
|
|
*/
|
|
|
|
/** @file singleton-ref.hpp
|
|
** Helper for singleton-kind access without managing object creation and lifecycle.
|
|
** A typical usage scenario is when implementing C Language Interfaces without any
|
|
** canonical access to some "this" pointer. In this case
|
|
** - an instance of the \c Access policy class is created "somewhere" (usually as
|
|
** global variable). Calls from within the C code would enter through this accessor.
|
|
** - when the actual service implementation class comes up, it creates an SingletonRef
|
|
** instance and thereby wires the (already existing) accessor up with \c *this
|
|
** - when the service goes down, access is closed automatically and reliably.
|
|
** Client code (from within C) should check the accessor (by \c bool check)
|
|
** prior to any access, because accessing a closed connection will throw
|
|
** (that's unfortunate, but at least throwing is better than segfaulting)
|
|
**
|
|
** @see gui::NotificationService usage example
|
|
*/
|
|
|
|
|
|
#ifndef LIB_SINGLETON_REF_H
|
|
#define LIB_SINGLETON_REF_H
|
|
|
|
|
|
#include "lib/error.hpp"
|
|
#include "lib/nocopy.hpp"
|
|
|
|
|
|
namespace lib {
|
|
|
|
namespace singleton {
|
|
|
|
/***********************************//**
|
|
* Detail/Policy class specifying
|
|
* how the SingletonRef can be accessed
|
|
*/
|
|
template<class TY>
|
|
class AccessAsReference
|
|
: util::NonCopyable
|
|
{
|
|
TY* obj_;
|
|
|
|
typedef AccessAsReference<TY> _ThisType;
|
|
|
|
public:
|
|
void
|
|
open (TY* instance)
|
|
{
|
|
ASSERT (!obj_, "Lifecycle error");
|
|
obj_ = instance;
|
|
}
|
|
|
|
void
|
|
close ()
|
|
{
|
|
ASSERT (obj_, "Lifecycle error");
|
|
obj_ = nullptr;
|
|
}
|
|
|
|
TY*
|
|
operator-> () const
|
|
{
|
|
if (!isValid())
|
|
throw lumiera::error::State("Target currently not available.");
|
|
return obj_;
|
|
}
|
|
|
|
explicit operator bool() const { return obj_; }
|
|
bool isValid() const { return obj_; }
|
|
};
|
|
|
|
} // namespace Singleton
|
|
|
|
|
|
|
|
|
|
/*********************************************************//**
|
|
* Helper template providing singleton access without managing
|
|
* object creation and lifecycle. Just the access to the
|
|
* implementation instance is handled: on creation, access is
|
|
* enabled, and disabled on destruction. Client code is assumed
|
|
* to invoke through the Access (template template param),
|
|
* handed in as ctor parameter.
|
|
* @param TY the actual type to be made accessible
|
|
* @param B a base class to inherit from; defaults to noncopyable
|
|
* @param Accessor how to implement the static instance access
|
|
*/
|
|
template< class TY
|
|
, class B = util::NonCopyable
|
|
, template<class> class Access = singleton::AccessAsReference
|
|
>
|
|
struct SingletonRef
|
|
: public B
|
|
{
|
|
|
|
typedef Access<TY> Accessor;
|
|
Accessor& accessor_;
|
|
|
|
SingletonRef(TY * instance, Accessor& acc)
|
|
: accessor_(acc)
|
|
{
|
|
accessor_.open (instance);
|
|
}
|
|
|
|
~SingletonRef()
|
|
{
|
|
accessor_.close ();
|
|
}
|
|
};
|
|
|
|
|
|
|
|
} // namespace lib
|
|
#endif
|