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XMLRegisterCleanup.hpp

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00001 /*
00002  * The Apache Software License, Version 1.1
00003  * 
00004  * Copyright (c) 1999-2000 The Apache Software Foundation.  All rights
00005  * reserved.
00006  * 
00007  * Redistribution and use in source and binary forms, with or without
00008  * modification, are permitted provided that the following conditions
00009  * are met:
00010  * 
00011  * 1. Redistributions of source code must retain the above copyright
00012  *    notice, this list of conditions and the following disclaimer. 
00013  * 
00014  * 2. Redistributions in binary form must reproduce the above copyright
00015  *    notice, this list of conditions and the following disclaimer in
00016  *    the documentation and/or other materials provided with the
00017  *    distribution.
00018  * 
00019  * 3. The end-user documentation included with the redistribution,
00020  *    if any, must include the following acknowledgment:  
00021  *       "This product includes software developed by the
00022  *        Apache Software Foundation (http://www.apache.org/)."
00023  *    Alternately, this acknowledgment may appear in the software itself,
00024  *    if and wherever such third-party acknowledgments normally appear.
00025  * 
00026  * 4. The names "Xerces" and "Apache Software Foundation" must
00027  *    not be used to endorse or promote products derived from this
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00029  *    permission, please contact apache\@apache.org.
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00031  * 5. Products derived from this software may not be called "Apache",
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00033  *    permission of the Apache Software Foundation.
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00035  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
00036  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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00047  * ====================================================================
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00049  * This software consists of voluntary contributions made by many
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00051  * originally based on software copyright (c) 1999, International
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00056 
00057 /*
00058  * $Id: XMLRegisterCleanup.hpp,v 1.4 2001/10/25 21:55:29 peiyongz Exp $
00059  * $Log: XMLRegisterCleanup.hpp,v $
00060  * Revision 1.4  2001/10/25 21:55:29  peiyongz
00061  * copy ctor explicity declared private to prevent supprise.
00062  *
00063  * Revision 1.3  2001/10/24 18:13:06  peiyongz
00064  * CVS tag added
00065  *
00066  *
00067  */
00068 
00069 #if !defined(XMLREGISTERCLEANUP_HPP)
00070 #define XMLREGISTERCLEANUP_HPP
00071 
00072 #include <util/Mutexes.hpp>
00073 
00074 // This is a mutex for exclusive use by this class
00075 extern XMLMutex* gXMLCleanupListMutex;
00076 
00077 // This is the head of a list of XMLRegisterCleanup objects that
00078 // is used during XMLPlatformUtils::Terminate() to find objects to
00079 // clean up
00080 class XMLRegisterCleanup;
00081 extern XMLRegisterCleanup* gXMLCleanupList;
00082 
00083 // 
00084 //  For internal use only.
00085 //
00086 //  This class is used by the platform utilities class to support 
00087 //  reinitialisation of global/static data which is lazily created. 
00088 //  Since that data is widely spread out the platform utilities
00089 //  class cannot know about them directly. So, the code that creates such
00090 //  objects creates an registers a cleanup for the object. The platform
00091 //  termination call will iterate the list and delete the objects.
00092 //
00093 //  N.B. These objects need to be statically allocated.  I couldn't think
00094 //  of a neat way of ensuring this - can anyone else?
00095 
00096 class XMLRegisterCleanup
00097 {
00098 public :
00099     // The cleanup function to be called on XMLPlatformUtils::Terminate()
00100     typedef void (*XMLCleanupFn)();
00101     
00102     void doCleanup() {
00103         // When performing cleanup, we only do this once, but we can
00104         // cope if somehow we have been called twice.
00105         if (m_cleanupFn) 
00106             m_cleanupFn();
00107 
00108         // We need to remove "this" from the list
00109         // irregardless of the cleanup Function
00110         unregisterCleanup();
00111     }
00112 
00113     // This function is called during initialisation of static data to
00114     // register a function to be called on XMLPlatformUtils::Terminate.
00115     // It gives an object that uses static data an opportunity to reset
00116     // such data.
00117     void registerCleanup(XMLCleanupFn cleanupFn) {
00118         // Store the cleanup function
00119         m_cleanupFn = cleanupFn;
00120         
00121         // Add this object to the list head, if it is not already 
00122         // present - which it shouldn't be.
00123         // This is done under a mutex to ensure thread safety.
00124         gXMLCleanupListMutex->lock();
00125         if (!m_nextCleanup && !m_prevCleanup) {
00126             m_nextCleanup = gXMLCleanupList;
00127             gXMLCleanupList = this;
00128 
00129             if (m_nextCleanup) 
00130                 m_nextCleanup->m_prevCleanup = this;
00131         }
00132         gXMLCleanupListMutex->unlock();
00133     }
00134 
00135     // This function can be called either from XMLPlatformUtils::Terminate
00136     // to state that the cleanup has been performed and should not be
00137     // performed again, or from code that you have written that determines
00138     // that cleanup is no longer necessary.
00139     void unregisterCleanup() {
00140         gXMLCleanupListMutex->lock();
00141 
00142         //
00143         // To protect against some compiler's (eg hp11) optimization
00144         // to change "this" as they update gXMLCleanupList
00145         //
00146         // refer to 
00147         // void XMLPlatformUtils::Terminate()
00148         //       ... 
00149         //       while (gXMLCleanupList)
00150         //            gXMLCleanupList->doCleanup();
00151         //
00152 
00153         XMLRegisterCleanup *tmpThis = (XMLRegisterCleanup*) this;
00154 
00155         // Unlink this object from the cleanup list
00156         if (m_nextCleanup) m_nextCleanup->m_prevCleanup = m_prevCleanup;
00157         
00158         if (!m_prevCleanup) gXMLCleanupList = m_nextCleanup;
00159         else m_prevCleanup->m_nextCleanup = m_nextCleanup;
00160 
00161         gXMLCleanupListMutex->unlock();
00162         
00163         // Reset the object to the default state
00164         tmpThis->resetCleanup();
00165     }
00166 
00167     // The default constructor sets a state that ensures that this object
00168     // will do nothing
00169     XMLRegisterCleanup()
00170     {
00171         resetCleanup();
00172     }
00173 
00174 private:
00175 
00176     //
00177     // unsupported ctor and operator
00178     //
00179     XMLRegisterCleanup(const XMLRegisterCleanup&)
00180     {}
00181 
00182     // This is the cleanup function to be called
00183     XMLCleanupFn m_cleanupFn;
00184 
00185     // These are list pointers to the next/prev cleanup function to be called
00186     XMLRegisterCleanup *m_nextCleanup, *m_prevCleanup;
00187 
00188     // This function reinitialises the object to the default state
00189     void resetCleanup() {
00190         m_nextCleanup = 0;
00191         m_prevCleanup = 0;
00192         m_cleanupFn = 0;
00193     }
00194 };
00195 
00196 #endif


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