1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
|
// Copyright (C) 2014 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef EMUGL_SMART_PTR_H
#define EMUGL_SMART_PTR_H
#include <stddef.h>
namespace emugl {
// Hidden atomic ref-counting implementation.
class RefCount;
// Base class for all templated SmartPtr<> instances. Reduces
// template expansion and code. Consider this to be an implementation
// detail of SmartPtr<>, so don't rely on anything here.
class SmartPtrBase {
public:
// Defrault constructor.
SmartPtrBase() : mPtr(NULL), mRefCount(NULL) {}
// Normal constructor. This takes ownership of |ptr|, though only
// template instances are capable of destroying the object.
explicit SmartPtrBase(void* ptr);
// Copy-constructor, this increments the reference count.
SmartPtrBase(const SmartPtrBase& other);
// Assignment operator, also increments the reference count.
SmartPtrBase& operator=(const SmartPtrBase& other);
// Nothing happens in this constructor, the real work must be performed
// in subclasses.
~SmartPtrBase() {}
// Used to enable 'if (smart_ptr) { ... }' properly.
operator void*() const {
return mPtr;
}
// Return internal reference count value, only use for unit testing.
int getRefCount() const;
protected:
// Used internally to increment the reference count.
void addRef();
// Copy the |other| into this instance, returns the old pointer value
// if it needs to be destroyed by the caller, or NULL otherwise.
void* copyFrom(const SmartPtrBase& other);
// Used internally to decrement the reference count, if it reaches 0,
// returns the pointer to be destroyed, NULL otherwise.
void* release();
void* mPtr;
RefCount* mRefCount;
};
// The real template class to be used for smart pointers.
// Typical uses:
//
// SmartPtr<Foo> ptr(new Foo()); // takes ownership.
// SmartPtr<Foo> ptr2; // empty pointer.
// ptr2 = ptr; // copies pointer + increment reference count.
// Foo* obj = ptr.Ptr(); // access pointed object.
// ptr->DoStuff(); // operate directly on pointed object.
// (*ptr)->DoStuff(); // same here.
//
// On scope exit, the internal reference count is decremented and the
// object is deleted automatically when it reaches 0, indicating that
// there are no more owners.
//
// IMPORTANT: You need to be sure that only one 'chain' of smart pointers
// own a given object. I.e. the following is incorrect:
//
// Foo* foo = new Foo(); // create new instance.
// SmartPtr<Foo> ptr(foo); // |ptr| takes ownership of |foo|.
// SmartPtr<Foo> ptr2(foo); // |ptr2| takes also ownership of |foo|.
//
// The problem is that |ptr| and |ptr2| don't know anything about each
// other, and will not share the same reference count. Once a smart pointer
// owns an object, only use other smart pointers that are copy-constructed
// or assigned with the initial one to keep everything consistent.
template <class T>
class SmartPtr : public emugl::SmartPtrBase {
public:
// Default constructor. The instance holds a NULL pointer.
SmartPtr() : SmartPtrBase() {}
// Regular constructor, takes ownership of |ptr|.
explicit SmartPtr(T* ptr) : SmartPtrBase(ptr) {}
// Copy-constructor, |this| and |other| will share the same internal
// reference count, which is incremented by 1.
SmartPtr(const SmartPtr& other)
: SmartPtrBase(reinterpret_cast<const SmartPtrBase&>(other)) {}
// Assignment operator, same semantics as copy-constructor.
SmartPtr& operator=(const SmartPtr& other) {
void* old_ptr = copyFrom(static_cast<const SmartPtrBase&>(other));
if (old_ptr)
delete reinterpret_cast<T*>(old_ptr);
return *this;
}
// Destructor, decrements reference count and destroys the object
// if it reaches 0 (indicating this was the last owning smart pointer).
~SmartPtr() {
void* ptr = release();
if (ptr)
delete reinterpret_cast<T*>(ptr);
}
// Return owned object instance, or NULL.
T* Ptr() const {
return reinterpret_cast<T*>(mPtr);
}
// Return owned object instance, or NULL
const T* constPtr() const {
return reinterpret_cast<const T*>(mPtr);
}
// Operate directly on owned object.
T* operator->() const {
return Ptr();
}
// Return reference to owned object.
T& operator*() const {
return *Ptr();
}
};
} // namespace emugl
#endif // EMUGL_SMART_PTR_H
|
