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
  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                        { ++mRefCount; RCDEBUG(UP, mRefCount); }
  74         unsigned int unref() const      { RCDEBUG(DOWN, mRefCount - 1); return --mRefCount; }
  75
  76         // if you call this for anything but debug output, you will go to hell (free handbasket included)
  77         unsigned int refCountForDebuggingOnly() const { return mRefCount; }
  78
  79 private:
  80     mutable AtomicCounter<unsigned int> mRefCount;
  81 };
  82
  83
  84 //
  85 // A pointer type supported by reference counts.
  86 // T must be derived from RefCount.
  87 //
  88 template <class T>
  89 class RefPointer {
  90         template <class Sub> friend class RefPointer; // share with other instances
  91 public:
  92         RefPointer() : ptr(0) {}                        // default to NULL pointer
  93         RefPointer(const RefPointer& p) { if (p) p->ref(); ptr = p.ptr; }
  94         RefPointer(T *p) { if (p) p->ref(); ptr = p; }
  95
  96         template <class Sub>
  97         RefPointer(const RefPointer<Sub>& p) { if (p) p->ref(); ptr = p.ptr; }
  98
  99         ~RefPointer() { release(); }
 100
 101         RefPointer& operator = (const RefPointer& p)    { setPointer(p.ptr); return *this; }
 102         RefPointer& operator = (T * p)                                  { setPointer(p); return *this; }
 103
 104         template <class Sub>
 105         RefPointer& operator = (const RefPointer<Sub>& p) { setPointer(p.ptr); return *this; }
 106
 107         // dereference operations
 108     T* get () const                             { _check(); return ptr; }       // mimic auto_ptr
 109         operator T * () const           { _check(); return ptr; }
 110         T * operator -> () const        { _check(); return ptr; }
 111         T & operator * () const         { _check(); return *ptr; }
 112
 113 protected:
 114         void release()
 115     {
 116         if (ptr && ptr->unref() == 0)
 117         {
 118             delete ptr;
 119             ptr = NULL;
 120         }
 121     }
 122
 123     void setPointer(T *p) { if (p) p->ref(); release(); ptr = p; }
 124
 125         void _check() const { }
 126
 127         T *ptr;
 128 };
 129
 130 template <class T>
 131 bool operator <(const RefPointer<T> &r1, const RefPointer<T> &r2)
 132 {
 133         T *p1 = r1.get(), *p2 = r2.get();
 134         return p1 && p2 ? *p1 < *p2 : p1 < p2;
 135 }
 136
 137 template <class T>
 138 bool operator ==(const RefPointer<T> &r1, const RefPointer<T> &r2)
 139 {
 140         T *p1 = r1.get(), *p2 = r2.get();
 141         return p1 && p2 ? *p1 == *p2 : p1 == p2;
 142 }
 143
 144 template <class T>
 145 bool operator !=(const RefPointer<T> &r1, const RefPointer<T> &r2)
 146 {
 147         T *p1 = r1.get(), *p2 = r2.get();
 148         return p1 && p2 ? *p1 != *p2 : p1 != p2;
 149 }
 150
 151 } // end namespace Security
 152
 153 #endif // !_SECURITY_REFCOUNT_H_