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      1 /*
      2  * libjingle
      3  * Copyright 2004--2005, Google Inc.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions are met:
      7  *
      8  *  1. Redistributions of source code must retain the above copyright notice,
      9  *     this list of conditions and the following disclaimer.
     10  *  2. Redistributions in binary form must reproduce the above copyright notice,
     11  *     this list of conditions and the following disclaimer in the documentation
     12  *     and/or other materials provided with the distribution.
     13  *  3. The name of the author may not be used to endorse or promote products
     14  *     derived from this software without specific prior written permission.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
     17  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
     18  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
     19  * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     20  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
     21  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
     22  * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
     23  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
     24  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
     25  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     26  */
     27 
     28 /*
     29  * linked_ptr - simple reference linked pointer
     30  * (like reference counting, just using a linked list of the references
     31  * instead of their count.)
     32  *
     33  * The implementation stores three pointers for every linked_ptr, but
     34  * does not allocate anything on the free store.
     35  */
     36 
     37 #ifndef TALK_BASE_LINKED_PTR_H__
     38 #define TALK_BASE_LINKED_PTR_H__
     39 
     40 namespace talk_base {
     41 
     42 /* For ANSI-challenged compilers, you may want to #define
     43  * NO_MEMBER_TEMPLATES, explicit or mutable */
     44 #define NO_MEMBER_TEMPLATES
     45 
     46 template <class X> class linked_ptr
     47 {
     48 public:
     49 
     50 #ifndef NO_MEMBER_TEMPLATES
     51 #   define TEMPLATE_FUNCTION template <class Y>
     52     TEMPLATE_FUNCTION friend class linked_ptr<Y>;
     53 #else
     54 #   define TEMPLATE_FUNCTION
     55     typedef X Y;
     56 #endif
     57 
     58     typedef X element_type;
     59 
     60     explicit linked_ptr(X* p = 0) throw()
     61         : itsPtr(p) {itsPrev = itsNext = this;}
     62     ~linked_ptr()
     63         {release();}
     64     linked_ptr(const linked_ptr& r) throw()
     65         {acquire(r);}
     66     linked_ptr& operator=(const linked_ptr& r)
     67     {
     68         if (this != &r) {
     69             release();
     70             acquire(r);
     71         }
     72         return *this;
     73     }
     74 
     75 #ifndef NO_MEMBER_TEMPLATES
     76     template <class Y> friend class linked_ptr<Y>;
     77     template <class Y> linked_ptr(const linked_ptr<Y>& r) throw()
     78         {acquire(r);}
     79     template <class Y> linked_ptr& operator=(const linked_ptr<Y>& r)
     80     {
     81         if (this != &r) {
     82             release();
     83             acquire(r);
     84         }
     85         return *this;
     86     }
     87 #endif // NO_MEMBER_TEMPLATES
     88 
     89     X& operator*()  const throw()   {return *itsPtr;}
     90     X* operator->() const throw()   {return itsPtr;}
     91     X* get()        const throw()   {return itsPtr;}
     92     bool unique()   const throw()   {return itsPrev ? itsPrev==this : true;}
     93 
     94 private:
     95     X*                          itsPtr;
     96     mutable const linked_ptr*   itsPrev;
     97     mutable const linked_ptr*   itsNext;
     98 
     99     void acquire(const linked_ptr& r) throw()
    100     { // insert this to the list
    101         itsPtr = r.itsPtr;
    102         itsNext = r.itsNext;
    103         itsNext->itsPrev = this;
    104         itsPrev = &r;
    105 #ifndef mutable
    106         r.itsNext = this;
    107 #else // for ANSI-challenged compilers
    108         (const_cast<linked_ptr<X>*>(&r))->itsNext = this;
    109 #endif
    110     }
    111 
    112 #ifndef NO_MEMBER_TEMPLATES
    113     template <class Y> void acquire(const linked_ptr<Y>& r) throw()
    114     { // insert this to the list
    115         itsPtr = r.itsPtr;
    116         itsNext = r.itsNext;
    117         itsNext->itsPrev = this;
    118         itsPrev = &r;
    119 #ifndef mutable
    120         r.itsNext = this;
    121 #else // for ANSI-challenged compilers
    122         (const_cast<linked_ptr<X>*>(&r))->itsNext = this;
    123 #endif
    124     }
    125 #endif // NO_MEMBER_TEMPLATES
    126 
    127     void release()
    128     { // erase this from the list, delete if unique
    129         if (unique()) delete itsPtr;
    130         else {
    131             itsPrev->itsNext = itsNext;
    132             itsNext->itsPrev = itsPrev;
    133             itsPrev = itsNext = 0;
    134         }
    135         itsPtr = 0;
    136     }
    137 };
    138 
    139 } // namespace talk_base
    140 
    141 #endif // TALK_BASE_LINKED_PTR_H__
    142 
    143