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      1 /*
      2  * Copyright (C) 2006, 2007, 2009 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 #ifndef NDEBUG
     27 #include <wtf/Threading.h>
     28 #endif
     29 
     30 namespace WebCore {
     31 
     32 template<class T> class TreeShared : public Noncopyable {
     33 public:
     34     TreeShared(int initialRefCount = 1)
     35         : m_refCount(initialRefCount)
     36         , m_parent(0)
     37     {
     38         ASSERT(isMainThread());
     39 #ifndef NDEBUG
     40         m_deletionHasBegun = false;
     41         m_inRemovedLastRefFunction = false;
     42 #endif
     43     }
     44     virtual ~TreeShared()
     45     {
     46         ASSERT(isMainThread());
     47         ASSERT(!m_refCount);
     48         ASSERT(m_deletionHasBegun);
     49     }
     50 
     51     void ref()
     52     {
     53         ASSERT(isMainThread());
     54         ASSERT(!m_deletionHasBegun);
     55         ASSERT(!m_inRemovedLastRefFunction);
     56         ++m_refCount;
     57     }
     58 
     59     void deref()
     60     {
     61         ASSERT(isMainThread());
     62         ASSERT(m_refCount >= 0);
     63         ASSERT(!m_deletionHasBegun);
     64         ASSERT(!m_inRemovedLastRefFunction);
     65         if (--m_refCount <= 0 && !m_parent) {
     66 #ifndef NDEBUG
     67             m_inRemovedLastRefFunction = true;
     68 #endif
     69             removedLastRef();
     70         }
     71     }
     72 
     73     bool hasOneRef() const
     74     {
     75         ASSERT(!m_deletionHasBegun);
     76         ASSERT(!m_inRemovedLastRefFunction);
     77         return m_refCount == 1;
     78     }
     79 
     80     int refCount() const
     81     {
     82         return m_refCount;
     83     }
     84 
     85     void setParent(T* parent)
     86     {
     87         ASSERT(isMainThread());
     88         m_parent = parent;
     89     }
     90 
     91     T* parent() const
     92     {
     93         ASSERT(isMainThread());
     94         return m_parent;
     95     }
     96 
     97 #ifndef NDEBUG
     98     bool m_deletionHasBegun;
     99     bool m_inRemovedLastRefFunction;
    100 #endif
    101 
    102 private:
    103     virtual void removedLastRef()
    104     {
    105 #ifndef NDEBUG
    106         m_deletionHasBegun = true;
    107 #endif
    108         delete this;
    109     }
    110 
    111     int m_refCount;
    112     T* m_parent;
    113 };
    114 
    115 }
    116 
    117 #endif // TreeShared.h
    118