third_party/WebKit/Source/wtf/RefCounted.h

   1 /*
   2  * Copyright (C) 2006, 2007, 2008, 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 RefCounted_h
  22 #define RefCounted_h
  23
  24 #include "wtf/Assertions.h"
  25 #include "wtf/FastAllocBase.h"
  26 #include "wtf/InstanceCounter.h"
  27 #include "wtf/Noncopyable.h"
  28 #include "wtf/WTFExport.h"
  29
  30 #if ENABLE(ASSERT)
  31 #define CHECK_REF_COUNTED_LIFECYCLE 1
  32 #include "wtf/ThreadRestrictionVerifier.h"
  33 #else
  34 #define CHECK_REF_COUNTED_LIFECYCLE 0
  35 #endif
  36
  37 namespace WTF {
  38
  39 // This base class holds the non-template methods and attributes.
  40 // The RefCounted class inherits from it reducing the template bloat
  41 // generated by the compiler (technique called template hoisting).
  42 class WTF_EXPORT RefCountedBase {
  43 public:
  44     void ref()
  45     {
  46 #if CHECK_REF_COUNTED_LIFECYCLE
  47         // Start thread verification as soon as the ref count gets to 2. This
  48         // heuristic reflects the fact that items are often created on one thread
  49         // and then given to another thread to be used.
  50         // FIXME: Make this restriction tigher. Especially as we move to more
  51         // common methods for sharing items across threads like CrossThreadCopier.h
  52         // We should be able to add a "detachFromThread" method to make this explicit.
  53         if (m_refCount == 1)
  54             m_verifier.setShared(true);
  55         // If this assert fires, it either indicates a thread safety issue or
  56         // that the verification needs to change. See ThreadRestrictionVerifier for
  57         // the different modes.
  58         ASSERT(m_verifier.isSafeToUse());
  59         ASSERT(!m_adoptionIsRequired);
  60 #endif
  61         ASSERT_WITH_SECURITY_IMPLICATION(!m_deletionHasBegun);
  62         ++m_refCount;
  63     }
  64
  65     bool hasOneRef() const
  66     {
  67         ASSERT_WITH_SECURITY_IMPLICATION(!m_deletionHasBegun);
  68 #if CHECK_REF_COUNTED_LIFECYCLE
  69         ASSERT(m_verifier.isSafeToUse());
  70 #endif
  71         return m_refCount == 1;
  72     }
  73
  74     int refCount() const
  75     {
  76 #if CHECK_REF_COUNTED_LIFECYCLE
  77         ASSERT(m_verifier.isSafeToUse());
  78 #endif
  79         return m_refCount;
  80     }
  81
  82 protected:
  83     RefCountedBase()
  84         : m_refCount(1)
  85 #if ENABLE(SECURITY_ASSERT)
  86         , m_deletionHasBegun(false)
  87 #endif
  88 #if CHECK_REF_COUNTED_LIFECYCLE
  89         , m_adoptionIsRequired(true)
  90 #endif
  91     {
  92     }
  93
  94     ~RefCountedBase()
  95     {
  96         ASSERT_WITH_SECURITY_IMPLICATION(m_deletionHasBegun);
  97 #if CHECK_REF_COUNTED_LIFECYCLE
  98         ASSERT(!m_adoptionIsRequired);
  99 #endif
 100     }
 101
 102     // Returns whether the pointer should be freed or not.
 103     bool derefBase()
 104     {
 105         ASSERT_WITH_SECURITY_IMPLICATION(!m_deletionHasBegun);
 106 #if CHECK_REF_COUNTED_LIFECYCLE
 107         ASSERT(m_verifier.isSafeToUse());
 108         ASSERT(!m_adoptionIsRequired);
 109 #endif
 110
 111         ASSERT(m_refCount > 0);
 112         --m_refCount;
 113         if (!m_refCount) {
 114 #if ENABLE(SECURITY_ASSERT)
 115             m_deletionHasBegun = true;
 116 #endif
 117             return true;
 118         }
 119
 120 #if CHECK_REF_COUNTED_LIFECYCLE
 121         // Stop thread verification when the ref goes to 1 because it
 122         // is safe to be passed to another thread at this point.
 123         if (m_refCount == 1)
 124             m_verifier.setShared(false);
 125 #endif
 126         return false;
 127     }
 128
 129 #if CHECK_REF_COUNTED_LIFECYCLE
 130     bool deletionHasBegun() const
 131     {
 132         return m_deletionHasBegun;
 133     }
 134 #endif
 135
 136 private:
 137
 138 #if CHECK_REF_COUNTED_LIFECYCLE || ENABLE(SECURITY_ASSERT)
 139     friend void adopted(RefCountedBase*);
 140 #endif
 141
 142     int m_refCount;
 143 #if ENABLE(SECURITY_ASSERT)
 144     bool m_deletionHasBegun;
 145 #endif
 146 #if CHECK_REF_COUNTED_LIFECYCLE
 147     bool m_adoptionIsRequired;
 148     ThreadRestrictionVerifier m_verifier;
 149 #endif
 150 };
 151
 152 #if CHECK_REF_COUNTED_LIFECYCLE || ENABLE(SECURITY_ASSERT)
 153 inline void adopted(RefCountedBase* object)
 154 {
 155     if (!object)
 156         return;
 157     ASSERT_WITH_SECURITY_IMPLICATION(!object->m_deletionHasBegun);
 158 #if CHECK_REF_COUNTED_LIFECYCLE
 159     object->m_adoptionIsRequired = false;
 160 #endif
 161 }
 162 #endif
 163
 164 template<typename T> class RefCounted : public RefCountedBase {
 165     WTF_MAKE_NONCOPYABLE(RefCounted);
 166     WTF_MAKE_FAST_ALLOCATED(RefCounted);
 167
 168 public:
 169     void deref()
 170     {
 171         if (derefBase())
 172             delete static_cast<T*>(this);
 173     }
 174
 175 protected:
 176 #ifdef ENABLE_INSTANCE_COUNTER
 177     RefCounted()
 178     {
 179         incrementInstanceCount<T>(static_cast<T*>(this));
 180     }
 181
 182     ~RefCounted()
 183     {
 184         decrementInstanceCount<T>(static_cast<T*>(this));
 185     }
 186 #else
 187     RefCounted()
 188     {
 189     }
 190 #endif
 191 };
 192
 193 } // namespace WTF
 194
 195 using WTF::RefCounted;
 196
 197 #endif // RefCounted_h