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,
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  18  * Please see the License for the specific language governing rights and
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  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 // Uncomment to debug refcounts
  53 //# define DEBUG_REFCOUNTS 1
  54
  55 #if DEBUG_REFCOUNTS
  56 # define RCDEBUG_CREATE()   secinfo("refcount", "%p: CREATE", this)
  57 # define RCDEBUG(_kind, n)  secinfo("refcount", "%p: %s: %d", this, #_kind, n)
  58 #else
  59 # define RCDEBUG_CREATE()         /* nothing */
  60 # define RCDEBUG(kind, _args...)  /* 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 private:
  87     volatile mutable int32_t mRefCount;
  88 };
  89
  90
  91 //
  92 // A pointer type supported by reference counts.
  93 // T must be derived from RefCount.
  94 //
  95 template <class T>
  96 class RefPointer {
  97         template <class Sub> friend class RefPointer; // share with other instances
  98 public:
  99         RefPointer() : ptr(0) {}                        // default to NULL pointer
 100         RefPointer(const RefPointer& p) { if (p) p->ref(); ptr = p.ptr; }
 101         RefPointer(T *p) { if (p) p->ref(); ptr = p; }
 102
 103         template <class Sub>
 104         RefPointer(const RefPointer<Sub>& p) { if (p) p->ref(); ptr = p.ptr; }
 105
 106         ~RefPointer() { release(); }
 107
 108         RefPointer& operator = (const RefPointer& p)    { setPointer(p.ptr); return *this; }
 109         RefPointer& operator = (T * p)                                  { setPointer(p); return *this; }
 110
 111         template <class Sub>
 112         RefPointer& operator = (const RefPointer<Sub>& p) { setPointer(p.ptr); return *this; }
 113
 114         // dereference operations
 115     T* get () const                             { _check(); return ptr; }       // mimic unique_ptr
 116         operator T * () const           { _check(); return ptr; }
 117         T * operator -> () const        { _check(); return ptr; }
 118         T & operator * () const         { _check(); return *ptr; }
 119
 120 protected:
 121         void release_internal()
 122     {
 123         if (ptr && ptr->unref() == 0)
 124         {
 125             delete ptr;
 126             ptr = NULL;
 127         }
 128     }
 129
 130     void release()
 131     {
 132         StLock<Mutex> mutexLock(mMutex);
 133         release_internal();
 134     }
 135
 136     void setPointer(T *p)
 137     {
 138         StLock<Mutex> mutexLock(mMutex);
 139         if (p)
 140         {
 141             p->ref();
 142         }
 143
 144         release_internal();
 145         ptr = p;
 146     }
 147
 148         void _check() const { }
 149
 150         T *ptr;
 151     Mutex mMutex;
 152 };
 153
 154 template <class T>
 155 bool operator <(const RefPointer<T> &r1, const RefPointer<T> &r2)
 156 {
 157         T *p1 = r1.get(), *p2 = r2.get();
 158         return p1 && p2 ? *p1 < *p2 : p1 < p2;
 159 }
 160
 161 template <class T>
 162 bool operator ==(const RefPointer<T> &r1, const RefPointer<T> &r2)
 163 {
 164         T *p1 = r1.get(), *p2 = r2.get();
 165         return p1 && p2 ? *p1 == *p2 : p1 == p2;
 166 }
 167
 168 template <class T>
 169 bool operator !=(const RefPointer<T> &r1, const RefPointer<T> &r2)
 170 {
 171         T *p1 = r1.get(), *p2 = r2.get();
 172         return p1 && p2 ? *p1 != *p2 : p1 != p2;
 173 }
 174
 175 } // end namespace Security
 176
 177 #endif // !_SECURITY_REFCOUNT_H_