Singleton.h revision 4e0c1f27fdefdd9b0208ea64542c1e39d9327eb9 
1/*
2 * Copyright (C) 2007 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef ANDROID_UTILS_SINGLETON_H
18#define ANDROID_UTILS_SINGLETON_H
19
20#include <stdint.h>
21#include <sys/types.h>
22#include <utils/threads.h>
23
24namespace android {
25// ---------------------------------------------------------------------------
26
27template <typename TYPE>
28class Singleton
29{
30public:
31    static TYPE& getInstance() {
32        Mutex::Autolock _l(sLock);
33        TYPE* instance = sInstance;
34        if (instance == 0) {
35            instance = new TYPE();
36            sInstance = instance;
37        }
38        return *instance;
39    }
40
41    static bool hasInstance() {
42        Mutex::Autolock _l(sLock);
43        return sInstance != 0;
44    }
45
46protected:
47    ~Singleton() { };
48    Singleton() { };
49
50private:
51    Singleton(const Singleton&);
52    Singleton& operator = (const Singleton&);
53    static Mutex sLock;
54    static TYPE* sInstance;
55};
56
57/*
58 * use ANDROID_SINGLETON_STATIC_INSTANCE(TYPE) in your implementation file
59 * (eg: <TYPE>.cpp) to create the static instance of Singleton<>'s attributes,
60 * and avoid to have a copy of them in each compilation units Singleton<TYPE>
61 * is used.
62 * NOTE: we use a version of Mutex ctor that takes a parameter, because
63 * for some unknown reason using the default ctor doesn't emit the variable!
64 */
65
66#define ANDROID_SINGLETON_STATIC_INSTANCE(TYPE)                 \
67    template class Singleton< TYPE >;                           \
68    template<> Mutex Singleton< TYPE >::sLock(Mutex::PRIVATE);  \
69    template<> TYPE* Singleton< TYPE >::sInstance(0);
70
71
72// ---------------------------------------------------------------------------
73}; // namespace android
74
75#endif // ANDROID_UTILS_SINGLETON_H
76
77