Ichthyostega
974c670d41
to make them stand out more prominently, some entity comments where started with a line of starts. Unfortunately, doxygen (and javadoc) only recogise comments which are started exactly with /** This caused quite some comments to be ignored by doxygen. Credits to Hendrik Boom for spotting this problem! A workaround is to end the line of stars with *//**
136 lines
4.1 KiB
C++
136 lines
4.1 KiB
C++
/*
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SINGLETON-REF.hpp - helper template providing singleton-like access for implementation code
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Copyright (C) Lumiera.org
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2008, Hermann Vosseler <Ichthyostega@web.de>
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License as
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published by the Free Software Foundation; either version 2 of
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the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/** @file singleton-ref.hpp
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** Helper for singleton-kind access without managing object creation and lifecycle.
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** A typical usage scenario is when implementing C Language Interfaces without any
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** canonical access to some "this" pointer. In this case
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** - an instance of the \c Access policy class is created "somewhere" (usually as
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** global variable). Calls from within the C code would enter through this accessor.
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** - when the actual service implementation class comes up, it creates an SingletonRef
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** instance and thereby wires the (already existing) accessor up with \c *this
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** - when the service goes down, access is closed automatically and reliably.
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** Client code (from within C) should check the accessor (by \c bool check)
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** prior to any access, because accessing a closed connection will throw
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** (that's unfortunate, but at least throwing is better than segfaulting)
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**
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** @see gui::NotificationService usage example
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*/
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#ifndef LIB_SINGLETON_REF_H
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#define LIB_SINGLETON_REF_H
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#include "lib/error.hpp"
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#include "lib/bool-checkable.hpp"
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#include <boost/noncopyable.hpp>
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namespace lib {
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namespace singleton {
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/***********************************//**
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* Detail/Policy class specifying
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* how the SingletonRef can be accessed
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*/
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template<class TY>
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class AccessAsReference
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: public lib::BoolCheckable<AccessAsReference<TY>
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, boost::noncopyable>
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{
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TY* obj_;
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typedef AccessAsReference<TY> _ThisType;
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public:
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void
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open (TY* instance)
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{
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ASSERT (!obj_, "Lifecycle error");
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obj_ = instance;
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}
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void
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close ()
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{
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ASSERT (obj_, "Lifecycle error");
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obj_ = 0;
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}
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TY*
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operator-> () const
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{
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if (!isValid())
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throw lumiera::error::State("Target currently not available.");
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return obj_;
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}
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bool isValid() const { return obj_; }
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};
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} // namespace Singleton
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/*********************************************************//**
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* Helper template providing singleton access without managing
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* object creation and lifecycle. Just the access to the
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* implementation instance is handled: on creation, access is
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* enabled, and disabled on destruction. Client code is assumed
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* to invoke through the Access (template template param),
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* handed in as ctor parameter.
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* @param TY the actual type to be made accessible
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* @param B a base class to inherit from; defaults to noncopyable
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* @param Accessor how to implement the static instance access
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*/
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template< class TY
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, class B = boost::noncopyable
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, template<class> class Access = singleton::AccessAsReference
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>
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struct SingletonRef
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: public B
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{
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typedef Access<TY> Accessor;
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Accessor& accessor_;
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SingletonRef(TY * instance, Accessor& acc)
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: accessor_(acc)
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{
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accessor_.open (instance);
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}
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~SingletonRef()
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{
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accessor_.close ();
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}
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};
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} // namespace lib
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#endif
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