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
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
|
/**
* @file llsingleton.h
*
* $LicenseInfo:firstyear=2002&license=viewerlgpl$
* Second Life Viewer Source Code
* Copyright (C) 2010, Linden Research, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation;
* version 2.1 of the License only.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
* Linden Research, Inc., 945 Battery Street, San Francisco, CA 94111 USA
* $/LicenseInfo$
*/
#ifndef LLSINGLETON_H
#define LLSINGLETON_H
#include "llerror.h" // *TODO: eliminate this
#include <typeinfo>
#include <boost/noncopyable.hpp>
// LLSingleton implements the getInstance() method part of the Singleton
// pattern. It can't make the derived class constructors protected, though, so
// you have to do that yourself.
//
// There are two ways to use LLSingleton. The first way is to inherit from it
// while using the typename that you'd like to be static as the template
// parameter, like so:
//
// class Foo: public LLSingleton<Foo>{};
//
// Foo& instance = Foo::instance();
//
// The second way is to use the singleton class directly, without inheritance:
//
// typedef LLSingleton<Foo> FooSingleton;
//
// Foo& instance = FooSingleton::instance();
//
// In this case, the class being managed as a singleton needs to provide an
// initSingleton() method since the LLSingleton virtual method won't be
// available
//
// As currently written, it is not thread-safe.
template <typename DERIVED_TYPE>
class LLSingleton : private boost::noncopyable
{
private:
typedef enum e_init_state
{
UNINITIALIZED,
CONSTRUCTING,
INITIALIZING,
INITIALIZED,
DELETED
} EInitState;
static DERIVED_TYPE* constructSingleton()
{
return new DERIVED_TYPE();
}
// stores pointer to singleton instance
struct SingletonLifetimeManager
{
SingletonLifetimeManager()
{
construct();
}
static void construct()
{
sData.mInitState = CONSTRUCTING;
sData.mInstance = constructSingleton();
sData.mInitState = INITIALIZING;
}
~SingletonLifetimeManager()
{
if (sData.mInitState != DELETED)
{
deleteSingleton();
}
}
};
public:
virtual ~LLSingleton()
{
sData.mInstance = NULL;
sData.mInitState = DELETED;
}
/**
* @brief Immediately delete the singleton.
*
* A subsequent call to LLProxy::getInstance() will construct a new
* instance of the class.
*
* LLSingletons are normally destroyed after main() has exited and the C++
* runtime is cleaning up statically-constructed objects. Some classes
* derived from LLSingleton have objects that are part of a runtime system
* that is terminated before main() exits. Calling the destructor of those
* objects after the termination of their respective systems can cause
* crashes and other problems during termination of the project. Using this
* method to destroy the singleton early can prevent these crashes.
*
* An example where this is needed is for a LLSingleton that has an APR
* object as a member that makes APR calls on destruction. The APR system is
* shut down explicitly before main() exits. This causes a crash on exit.
* Using this method before the call to apr_terminate() and NOT calling
* getInstance() again will prevent the crash.
*/
static void deleteSingleton()
{
delete sData.mInstance;
sData.mInstance = NULL;
sData.mInitState = DELETED;
}
static DERIVED_TYPE* getInstance()
{
static SingletonLifetimeManager sLifeTimeMgr;
switch (sData.mInitState)
{
case UNINITIALIZED:
// should never be uninitialized at this point
llassert(false);
return NULL;
case CONSTRUCTING:
LL_ERRS() << "Tried to access singleton " << typeid(DERIVED_TYPE).name() << " from singleton constructor!" << LL_ENDL;
return NULL;
case INITIALIZING:
// go ahead and flag ourselves as initialized so we can be reentrant during initialization
sData.mInitState = INITIALIZED;
// initialize singleton after constructing it so that it can reference other singletons which in turn depend on it,
// thus breaking cyclic dependencies
sData.mInstance->initSingleton();
return sData.mInstance;
case INITIALIZED:
return sData.mInstance;
case DELETED:
LL_WARNS() << "Trying to access deleted singleton " << typeid(DERIVED_TYPE).name() << " creating new instance" << LL_ENDL;
SingletonLifetimeManager::construct();
// same as first time construction
sData.mInitState = INITIALIZED;
sData.mInstance->initSingleton();
return sData.mInstance;
}
return NULL;
}
// Reference version of getInstance()
// Preferred over getInstance() as it disallows checking for NULL
static DERIVED_TYPE& instance()
{
return *getInstance();
}
// Has this singleton been created yet?
// Use this to avoid accessing singletons before they can safely be constructed.
static bool instanceExists()
{
return sData.mInitState == INITIALIZED;
}
private:
virtual void initSingleton() {}
struct SingletonData
{
// explicitly has a default constructor so that member variables are zero initialized in BSS
// and only changed by singleton logic, not constructor running during startup
EInitState mInitState;
DERIVED_TYPE* mInstance;
};
static SingletonData sData;
};
template<typename T>
typename LLSingleton<T>::SingletonData LLSingleton<T>::sData;
#endif
|
