OSX/libsecurity_utilities/lib/refcount.h

   1 /*
   2  * Copyright (c) 2000-2004,2011-2014 Apple Inc. All Rights Reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24
  25 /*
  26  */
  27 #ifndef _SECURITY_REFCOUNT_H_
  28 #define _SECURITY_REFCOUNT_H_
  29
  30 #include <security_utilities/threading.h>
  31 #include <libkern/OSAtomic.h>
  32
  33 namespace Security {
  34
  35
  36 //
  37 // RefCount/RefPointer - a simple reference counting facility.
  38 //
  39 // To make an object reference-counted, inherit from RefCount. To track refcounted
  40 // objects, use RefPointer<TheType>, where TheType must inherit from RefCount.
  41 //
  42 // RefCount is thread safe - any number of threads can hold and manipulate references
  43 // in parallel. It does however NOT protect the contents of your object - just the
  44 // reference count itself. If you need to share your object contents, you must provide
  45 // appropriate locking yourself.
  46 //
  47 // There is no (thread safe) way to determine whether you are the only thread holding
  48 // a pointer to a particular RefCount object. Thus there is no (thread safe)
  49 // way to "demand copy" a RefCount subclass. Trust me; it's been tried. Don't.
  50 //
  51
  52 #if !defined(DEBUG_REFCOUNTS)
  53 # define DEBUG_REFCOUNTS 1
  54 #endif
  55
  56 #if DEBUG_REFCOUNTS
  57 # define RCDEBUG(_kind, _args...)       SECURITY_DEBUG_REFCOUNT_##_kind((void *)this, ##_args)
  58 #else
  59 # define RCDEBUG(kind)  /* nothing */
  60 #endif
  61
  62
  63 //
  64 // Base class for reference counted objects
  65 //
  66 class RefCount {
  67 public:
  68         RefCount() : mRefCount(0) { RCDEBUG(CREATE); }
  69
  70 protected:
  71         template <class T> friend class RefPointer;
  72
  73         void ref() const
  74     {
  75         OSAtomicIncrement32(&mRefCount);
  76         RCDEBUG(UP, mRefCount);
  77     }
  78
  79     unsigned int unref() const
  80     {
  81         RCDEBUG(DOWN, mRefCount - 1);
  82         return OSAtomicDecrement32(&mRefCount);
  83     }
  84
  85         // if you call this for anything but debug output, you will go to hell (free handbasket included)
  86         unsigned int refCountForDebuggingOnly() const { return mRefCount; }
  87
  88 private:
  89     volatile mutable int32_t mRefCount;
  90 };
  91
  92
  93 //
  94 // A pointer type supported by reference counts.
  95 // T must be derived from RefCount.
  96 //
  97 template <class T>
  98 class RefPointer {
  99         template <class Sub> friend class RefPointer; // share with other instances
 100 public:
 101         RefPointer() : ptr(0) {}                        // default to NULL pointer
 102         RefPointer(const RefPointer& p) { if (p) p->ref(); ptr = p.ptr; }
 103         RefPointer(T *p) { if (p) p->ref(); ptr = p; }
 104
 105         template <class Sub>
 106         RefPointer(const RefPointer<Sub>& p) { if (p) p->ref(); ptr = p.ptr; }
 107
 108         ~RefPointer() { release(); }
 109
 110         RefPointer& operator = (const RefPointer& p)    { setPointer(p.ptr); return *this; }
 111         RefPointer& operator = (T * p)                                  { setPointer(p); return *this; }
 112
 113         template <class Sub>
 114         RefPointer& operator = (const RefPointer<Sub>& p) { setPointer(p.ptr); return *this; }
 115
 116         // dereference operations
 117     T* get () const                             { _check(); return ptr; }       // mimic auto_ptr
 118         operator T * () const           { _check(); return ptr; }
 119         T * operator -> () const        { _check(); return ptr; }
 120         T & operator * () const         { _check(); return *ptr; }
 121
 122 protected:
 123         void release_internal()
 124     {
 125         if (ptr && ptr->unref() == 0)
 126         {
 127             delete ptr;
 128             ptr = NULL;
 129         }
 130     }
 131
 132     void release()
 133     {
 134         StLock<Mutex> mutexLock(mMutex);
 135         release_internal();
 136     }
 137
 138     void setPointer(T *p)
 139     {
 140         StLock<Mutex> mutexLock(mMutex);
 141         if (p)
 142         {
 143             p->ref();
 144         }
 145
 146         release_internal();
 147         ptr = p;
 148     }
 149
 150         void _check() const { }
 151
 152         T *ptr;
 153     Mutex mMutex;
 154 };
 155
 156 template <class T>
 157 bool operator <(const RefPointer<T> &r1, const RefPointer<T> &r2)
 158 {
 159         T *p1 = r1.get(), *p2 = r2.get();
 160         return p1 && p2 ? *p1 < *p2 : p1 < p2;
 161 }
 162
 163 template <class T>
 164 bool operator ==(const RefPointer<T> &r1, const RefPointer<T> &r2)
 165 {
 166         T *p1 = r1.get(), *p2 = r2.get();
 167         return p1 && p2 ? *p1 == *p2 : p1 == p2;
 168 }
 169
 170 template <class T>
 171 bool operator !=(const RefPointer<T> &r1, const RefPointer<T> &r2)
 172 {
 173         T *p1 = r1.get(), *p2 = r2.get();
 174         return p1 && p2 ? *p1 != *p2 : p1 != p2;
 175 }
 176
 177 } // end namespace Security
 178
 179 #endif // !_SECURITY_REFCOUNT_H_