include/tools/weakbase.h

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   5  * This Source Code Form is subject to the terms of the Mozilla Public
   6  * License, v. 2.0. If a copy of the MPL was not distributed with this
   7  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   8  *
   9  * This file incorporates work covered by the following license notice:
  10  *
  11  *   Licensed to the Apache Software Foundation (ASF) under one or more
  12  *   contributor license agreements. See the NOTICE file distributed
  13  *   with this work for additional information regarding copyright
  14  *   ownership. The ASF licenses this file to you under the Apache
  15  *   License, Version 2.0 (the "License"); you may not use this file
  16  *   except in compliance with the License. You may obtain a copy of
  17  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  18  */
  19 #ifndef INCLUDED_TOOLS_WEAKBASE_H
  20 #define INCLUDED_TOOLS_WEAKBASE_H
  21
  22 #include <sal/types.h>
  23 #include <osl/diagnose.h>
  24 #include <rtl/ref.hxx>
  25
  26 /** the template classes in this header are helper to implement weak references
  27     to implementation objects that are not refcounted.
  28
  29     THIS IS NOT THREADSAFE
  30
  31     Use this only to have 'safe' pointers to implementation objects that you
  32     don't own but that you reference with a pointer.
  33
  34     Example:
  35
  36     class ImplClass : public tools::WeakBase< ImplClass >
  37     {
  38         ~ImplClass() { clearWeek(); } // not needed but safer, see method description
  39         ...
  40     };
  41
  42     class UserClass
  43     {
  44         tools::WeakReference< ImplClass > mxWeakRef;
  45
  46         UserClass( ImplClass* pOjbect ) : mxWeakRef( pObject ) {}
  47
  48         DoSomething()
  49         {
  50             if( mxWeakRef.is() )
  51                 mxWeakRef->DoSomethingMore();
  52         }
  53     };
  54 */
  55 namespace tools
  56 {
  57
  58 /** private connection helper, do not use directly */
  59 template <class reference_type>
  60 struct WeakConnection
  61 {
  62     sal_Int32   mnRefCount;
  63     reference_type* mpReference;
  64
  65     WeakConnection( reference_type* pReference ) : mnRefCount( 0 ), mpReference( pReference ) {};
  66     void acquire() { mnRefCount++; }
  67     void release() { mnRefCount--; if( mnRefCount == 0 ) delete this; }
  68 };
  69
  70 /** template implementation to hold a weak reference to an instance of type reference_type */
  71 template <class reference_type>
  72 class SAL_WARN_UNUSED WeakReference
  73 {
  74 public:
  75     /** constructs an empty reference */
  76     inline WeakReference();
  77
  78     /** constructs a reference with a pointer to a class derived from WeakBase */
  79     inline WeakReference( reference_type* pReference );
  80
  81     /** constructs a reference from another reference */
  82     inline WeakReference( const WeakReference< reference_type >& rWeakRef );
  83
  84     /** constructs a reference from another reference */
  85     inline WeakReference( WeakReference< reference_type >&& rWeakRef );
  86
  87     /** returns true if the reference object is not null and still alive */
  88     inline bool is() const;
  89
  90     /** returns the pointer to the reference object or null */
  91     inline reference_type * get() const;
  92
  93     /** sets this reference to the given object or null */
  94     inline void reset( reference_type* pReference );
  95
  96     /** returns the pointer to the reference object or null */
  97     inline reference_type * operator->() const;
  98
  99     /** returns true if this instance references pReferenceObject */
 100     inline bool operator== (const reference_type * pReferenceObject) const;
 101
 102     /** returns true if this instance and the given weakref reference the same object */
 103     inline bool operator== (const WeakReference<reference_type> & handle) const;
 104
 105     /** only needed for using this class with stl containers */
 106     inline bool operator!= (const WeakReference<reference_type> & handle) const;
 107
 108     /** only needed for using this class with stl containers */
 109     inline bool operator< (const WeakReference<reference_type> & handle) const;
 110
 111     /** only needed for using this class with stl containers */
 112     inline bool operator> (const WeakReference<reference_type> & handle) const;
 113
 114     /** the assignment operator */
 115     inline WeakReference<reference_type>& operator= (const WeakReference<reference_type> & handle);
 116
 117     /** the move assignment operator */
 118     inline WeakReference<reference_type>& operator= (WeakReference<reference_type> && handle);
 119
 120 private:
 121     rtl::Reference<WeakConnection< reference_type >> mpWeakConnection;
 122 };
 123
 124 /** derive your implementation classes from this class if you want them to support weak references */
 125 template <class reference_type>
 126 class WeakBase
 127 {
 128     friend class WeakReference<reference_type>;
 129
 130 public:
 131     inline WeakBase();
 132
 133     inline ~WeakBase();
 134     /** clears the reference pointer in all living weak references for this instance.
 135         Further created weak references will also be invalid.
 136         You should call this method in the d'tor of your derived classes for an early
 137         invalidate of all living weak references while your object is already inside
 138         it d'tor.
 139     */
 140     inline void clearWeak();
 141
 142 private:
 143     inline WeakConnection< reference_type >* getWeakConnection();
 144     rtl::Reference<WeakConnection< reference_type >> mpWeakConnection;
 145 };
 146
 147 }
 148
 149 #endif
 150
 151 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */