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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 
throw()43     explicit linked_ptr(X* p = 0) throw()
44         : itsPtr(p) {itsPrev = itsNext = this;}
~linked_ptr()45     ~linked_ptr()
46         {release();}
throw()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>;
linked_ptr(const linked_ptr<Y> & r)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 
throw()72     X& operator*()  const throw()   {return *itsPtr;}
73     X* operator->() const throw()   {return itsPtr;}
get()74     X* get()        const throw()   {return itsPtr;}
unique()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 
acquire(const linked_ptr & r)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
acquire(const linked_ptr<Y> & r)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 
release()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