libsecurity_utilities/lib/refcount.h

   1 /*
   2  * Copyright (c) 2000-2004 Apple Computer, 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         Based on code donated by Perry Kiehtreiber
  27  */
  28 #ifndef _SECURITY_REFCOUNT_H_
  29 #define _SECURITY_REFCOUNT_H_
  30
  31 #include <security_utilities/threading.h>
  32 #include <libkern/OSAtomic.h>
  33
  34 namespace Security {
  35
  36
  37 //
  38 // RefCount/RefPointer - a simple reference counting facility.
  39 //
  40 // To make an object reference-counted, inherit from RefCount. To track refcounted
  41 // objects, use RefPointer<TheType>, where TheType must inherit from RefCount.
  42 //
  43 // RefCount is thread safe - any number of threads can hold and manipulate references
  44 // in parallel. It does however NOT protect the contents of your object - just the
  45 // reference count itself. If you need to share your object contents, you must provide
  46 // appropriate locking yourself.
  47 //
  48 // There is no (thread safe) way to determine whether you are the only thread holding
  49 // a pointer to a particular RefCount object. Thus there is no (thread safe)
  50 // way to "demand copy" a RefCount subclass. Trust me; it's been tried. Don't.
  51 //
  52
  53 #if !defined(DEBUG_REFCOUNTS)
  54 # define DEBUG_REFCOUNTS 1
  55 #endif
  56
  57 #if DEBUG_REFCOUNTS
  58 # define RCDEBUG(_kind, _args...)       SECURITY_DEBUG_REFCOUNT_##_kind((void *)this, ##_args)
  59 #else
  60 # define RCDEBUG(kind)  /* nothing */
  61 #endif
  62
  63
  64 //
  65 // Base class for reference counted objects
  66 //
  67 class RefCount {
  68 public:
  69         RefCount() : mRefCount(0) { RCDEBUG(CREATE); }
  70
  71 protected:
  72         template <class T> friend class RefPointer;
  73
  74         void ref() const
  75     {
  76         OSAtomicIncrement32(&mRefCount);
  77         RCDEBUG(UP, mRefCount);
  78     }
  79
  80     unsigned int unref() const
  81     {
  82         RCDEBUG(DOWN, mRefCount - 1);
  83         return OSAtomicDecrement32(&mRefCount);
  84     }
  85
  86         // if you call this for anything but debug output, you will go to hell (free handbasket included)
  87         unsigned int refCountForDebuggingOnly() const { return mRefCount; }
  88
  89 private:
  90     volatile mutable int32_t mRefCount;
  91 };
  92
  93
  94 //
  95 // A pointer type supported by reference counts.
  96 // T must be derived from RefCount.
  97 //
  98 template <class T>
  99 class RefPointer {
 100         template <class Sub> friend class RefPointer; // share with other instances
 101 public:
 102         RefPointer() : ptr(0) {}                        // default to NULL pointer
 103         RefPointer(const RefPointer& p) { if (p) p->ref(); ptr = p.ptr; }
 104         RefPointer(T *p) { if (p) p->ref(); ptr = p; }
 105
 106         template <class Sub>
 107         RefPointer(const RefPointer<Sub>& p) { if (p) p->ref(); ptr = p.ptr; }
 108
 109         ~RefPointer() { release(); }
 110
 111         RefPointer& operator = (const RefPointer& p)    { setPointer(p.ptr); return *this; }
 112         RefPointer& operator = (T * p)                                  { setPointer(p); return *this; }
 113
 114         template <class Sub>
 115         RefPointer& operator = (const RefPointer<Sub>& p) { setPointer(p.ptr); return *this; }
 116
 117         // dereference operations
 118     T* get () const                             { _check(); return ptr; }       // mimic auto_ptr
 119         operator T * () const           { _check(); return ptr; }
 120         T * operator -> () const        { _check(); return ptr; }
 121         T & operator * () const         { _check(); return *ptr; }
 122
 123 protected:
 124         void release_internal()
 125     {
 126         if (ptr && ptr->unref() == 0)
 127         {
 128             delete ptr;
 129             ptr = NULL;
 130         }
 131     }
 132
 133     void release()
 134     {
 135         StLock<Mutex> mutexLock(mMutex);
 136         release_internal();
 137     }
 138
 139     void setPointer(T *p)
 140     {
 141         StLock<Mutex> mutexLock(mMutex);
 142         if (p)
 143         {
 144             p->ref();
 145         }
 146
 147         release_internal();
 148         ptr = p;
 149     }
 150
 151         void _check() const { }
 152
 153         T *ptr;
 154     Mutex mMutex;
 155 };
 156
 157 template <class T>
 158 bool operator <(const RefPointer<T> &r1, const RefPointer<T> &r2)
 159 {
 160         T *p1 = r1.get(), *p2 = r2.get();
 161         return p1 && p2 ? *p1 < *p2 : p1 < p2;
 162 }
 163
 164 template <class T>
 165 bool operator ==(const RefPointer<T> &r1, const RefPointer<T> &r2)
 166 {
 167         T *p1 = r1.get(), *p2 = r2.get();
 168         return p1 && p2 ? *p1 == *p2 : p1 == p2;
 169 }
 170
 171 template <class T>
 172 bool operator !=(const RefPointer<T> &r1, const RefPointer<T> &r2)
 173 {
 174         T *p1 = r1.get(), *p2 = r2.get();
 175         return p1 && p2 ? *p1 != *p2 : p1 != p2;
 176 }
 177
 178 } // end namespace Security
 179
 180 #endif // !_SECURITY_REFCOUNT_H_