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      1 /*
      2  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
      3  *
      4  *  Use of this source code is governed by a BSD-style license
      5  *  that can be found in the LICENSE file in the root of the source
      6  *  tree. An additional intellectual property rights grant can be found
      7  *  in the file PATENTS.  All contributing project authors may
      8  *  be found in the AUTHORS file in the root of the source tree.
      9  */
     10 
     11 /*
     12  * linked_ptr - simple reference linked pointer
     13  * (like reference counting, just using a linked list of the references
     14  * instead of their count.)
     15  *
     16  * The implementation stores three pointers for every linked_ptr, but
     17  * does not allocate anything on the free store.
     18  */
     19 
     20 #ifndef WEBRTC_BASE_LINKED_PTR_H__
     21 #define WEBRTC_BASE_LINKED_PTR_H__
     22 
     23 namespace rtc {
     24 
     25 /* For ANSI-challenged compilers, you may want to #define
     26  * NO_MEMBER_TEMPLATES, explicit or mutable */
     27 #define NO_MEMBER_TEMPLATES
     28 
     29 template <class X> class linked_ptr
     30 {
     31 public:
     32 
     33 #ifndef NO_MEMBER_TEMPLATES
     34 #   define TEMPLATE_FUNCTION template <class Y>
     35     TEMPLATE_FUNCTION friend class linked_ptr<Y>;
     36 #else
     37 #   define TEMPLATE_FUNCTION
     38     typedef X Y;
     39 #endif
     40 
     41     typedef X element_type;
     42 
     43     explicit linked_ptr(X* p = 0) throw()
     44         : itsPtr(p) {itsPrev = itsNext = this;}
     45     ~linked_ptr()
     46         {release();}
     47     linked_ptr(const linked_ptr& r) throw()
     48         {acquire(r);}
     49     linked_ptr& operator=(const linked_ptr& r)
     50     {
     51         if (this != &r) {
     52             release();
     53             acquire(r);
     54         }
     55         return *this;
     56     }
     57 
     58 #ifndef NO_MEMBER_TEMPLATES
     59     template <class Y> friend class linked_ptr<Y>;
     60     template <class Y> linked_ptr(const linked_ptr<Y>& r) throw()
     61         {acquire(r);}
     62     template <class Y> linked_ptr& operator=(const linked_ptr<Y>& r)
     63     {
     64         if (this != &r) {
     65             release();
     66             acquire(r);
     67         }
     68         return *this;
     69     }
     70 #endif // NO_MEMBER_TEMPLATES
     71 
     72     X& operator*()  const throw()   {return *itsPtr;}
     73     X* operator->() const throw()   {return itsPtr;}
     74     X* get()        const throw()   {return itsPtr;}
     75     bool unique()   const throw()   {return itsPrev ? itsPrev==this : true;}
     76 
     77 private:
     78     X*                          itsPtr;
     79     mutable const linked_ptr*   itsPrev;
     80     mutable const linked_ptr*   itsNext;
     81 
     82     void acquire(const linked_ptr& r) throw()
     83     { // insert this to the list
     84         itsPtr = r.itsPtr;
     85         itsNext = r.itsNext;
     86         itsNext->itsPrev = this;
     87         itsPrev = &r;
     88 #ifndef mutable
     89         r.itsNext = this;
     90 #else // for ANSI-challenged compilers
     91         (const_cast<linked_ptr<X>*>(&r))->itsNext = this;
     92 #endif
     93     }
     94 
     95 #ifndef NO_MEMBER_TEMPLATES
     96     template <class Y> void acquire(const linked_ptr<Y>& r) throw()
     97     { // insert this to the list
     98         itsPtr = r.itsPtr;
     99         itsNext = r.itsNext;
    100         itsNext->itsPrev = this;
    101         itsPrev = &r;
    102 #ifndef mutable
    103         r.itsNext = this;
    104 #else // for ANSI-challenged compilers
    105         (const_cast<linked_ptr<X>*>(&r))->itsNext = this;
    106 #endif
    107     }
    108 #endif // NO_MEMBER_TEMPLATES
    109 
    110     void release()
    111     { // erase this from the list, delete if unique
    112         if (unique()) delete itsPtr;
    113         else {
    114             itsPrev->itsNext = itsNext;
    115             itsNext->itsPrev = itsPrev;
    116             itsPrev = itsNext = 0;
    117         }
    118         itsPtr = 0;
    119     }
    120 };
    121 
    122 } // namespace rtc
    123 
    124 #endif // WEBRTC_BASE_LINKED_PTR_H__
    125 
    126