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      1 /*
      2  * Copyright (C) 2006, 2007, 2009, 2010 Apple Inc. All rights reserved.
      3  *
      4  * This library is free software; you can redistribute it and/or
      5  * modify it under the terms of the GNU Library General Public
      6  * License as published by the Free Software Foundation; either
      7  * version 2 of the License, or (at your option) any later version.
      8  *
      9  * This library is distributed in the hope that it will be useful,
     10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
     11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     12  * Library General Public License for more details.
     13  *
     14  * You should have received a copy of the GNU Library General Public License
     15  * along with this library; see the file COPYING.LIB.  If not, write to
     16  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
     17  * Boston, MA 02110-1301, USA.
     18  *
     19  */
     20 
     21 #ifndef TreeShared_h
     22 #define TreeShared_h
     23 
     24 #include <wtf/Assertions.h>
     25 #include <wtf/Noncopyable.h>
     26 #include <wtf/Threading.h>
     27 
     28 namespace WebCore {
     29 
     30 #ifndef NDEBUG
     31 template<typename T> class TreeShared;
     32 template<typename T> void adopted(TreeShared<T>*);
     33 #endif
     34 
     35 template<typename T> class TreeShared {
     36     WTF_MAKE_NONCOPYABLE(TreeShared);
     37 public:
     38     TreeShared()
     39         : m_refCount(1)
     40         , m_parent(0)
     41 #ifndef NDEBUG
     42         , m_adoptionIsRequired(true)
     43 #endif
     44     {
     45         ASSERT(isMainThread());
     46 #ifndef NDEBUG
     47         m_deletionHasBegun = false;
     48         m_inRemovedLastRefFunction = false;
     49 #endif
     50     }
     51     virtual ~TreeShared()
     52     {
     53         ASSERT(isMainThread());
     54         ASSERT(!m_refCount);
     55         ASSERT(m_deletionHasBegun);
     56         ASSERT(!m_adoptionIsRequired);
     57     }
     58 
     59     void ref()
     60     {
     61         ASSERT(isMainThread());
     62         ASSERT(!m_deletionHasBegun);
     63         ASSERT(!m_inRemovedLastRefFunction);
     64         ASSERT(!m_adoptionIsRequired);
     65         ++m_refCount;
     66     }
     67 
     68     void deref()
     69     {
     70         ASSERT(isMainThread());
     71         ASSERT(m_refCount >= 0);
     72         ASSERT(!m_deletionHasBegun);
     73         ASSERT(!m_inRemovedLastRefFunction);
     74         ASSERT(!m_adoptionIsRequired);
     75         if (--m_refCount <= 0 && !m_parent) {
     76 #ifndef NDEBUG
     77             m_inRemovedLastRefFunction = true;
     78 #endif
     79             removedLastRef();
     80         }
     81     }
     82 
     83     bool hasOneRef() const
     84     {
     85         ASSERT(!m_deletionHasBegun);
     86         ASSERT(!m_inRemovedLastRefFunction);
     87         return m_refCount == 1;
     88     }
     89 
     90     int refCount() const
     91     {
     92         return m_refCount;
     93     }
     94 
     95     void setParent(T* parent)
     96     {
     97         ASSERT(isMainThread());
     98         m_parent = parent;
     99     }
    100 
    101     T* parent() const
    102     {
    103         ASSERT(isMainThread());
    104         return m_parent;
    105     }
    106 
    107 #ifndef NDEBUG
    108     bool m_deletionHasBegun;
    109     bool m_inRemovedLastRefFunction;
    110 #endif
    111 
    112 protected:
    113     virtual void removedLastRef()
    114     {
    115 #ifndef NDEBUG
    116         m_deletionHasBegun = true;
    117 #endif
    118         delete this;
    119     }
    120 
    121 private:
    122 #ifndef NDEBUG
    123     friend void adopted<>(TreeShared<T>*);
    124 #endif
    125 
    126     int m_refCount;
    127     T* m_parent;
    128 #ifndef NDEBUG
    129     bool m_adoptionIsRequired;
    130 #endif
    131 };
    132 
    133 #ifndef NDEBUG
    134 
    135 template<typename T> inline void adopted(TreeShared<T>* object)
    136 {
    137     if (!object)
    138         return;
    139     ASSERT(!object->m_deletionHasBegun);
    140     ASSERT(!object->m_inRemovedLastRefFunction);
    141     object->m_adoptionIsRequired = false;
    142 }
    143 
    144 #endif
    145 
    146 }
    147 
    148 #endif // TreeShared.h
    149