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 
22 // some vendor code assumes they have atoi() after including this file.
23 #include <stdlib.h>
24 
25 #include <sys/types.h>
26 #include <utils/Mutex.h>
27 #include <cutils/compiler.h>
28 
29 namespace android {
30 // ---------------------------------------------------------------------------
31 
32 // Singleton<TYPE> may be used in multiple libraries, only one of which should
33 // define the static member variables using ANDROID_SINGLETON_STATIC_INSTANCE.
34 // Turn off -Wundefined-var-template so other users don't get:
35 // instantiation of variable 'android::Singleton<TYPE>::sLock' required here,
36 // but no definition is available
37 #if defined(__clang__)
38 #pragma clang diagnostic push
39 #pragma clang diagnostic ignored "-Wundefined-var-template"
40 #endif
41 
42 // DO NOT USE: Please use scoped static initialization. For instance:
43 //     MyClass& getInstance() {
44 //         static MyClass gInstance(...);
45 //         return gInstance;
46 //     }
47 template <typename TYPE>
48 class ANDROID_API Singleton
49 {
50 public:
getInstance()51     static TYPE& getInstance() {
52         Mutex::Autolock _l(sLock);
53         TYPE* instance = sInstance;
54         if (instance == nullptr) {
55             instance = new TYPE();
56             sInstance = instance;
57         }
58         return *instance;
59     }
60 
hasInstance()61     static bool hasInstance() {
62         Mutex::Autolock _l(sLock);
63         return sInstance != nullptr;
64     }
65 
66 protected:
~Singleton()67     ~Singleton() { }
Singleton()68     Singleton() { }
69 
70 private:
71     Singleton(const Singleton&);
72     Singleton& operator = (const Singleton&);
73     static Mutex sLock;
74     static TYPE* sInstance;
75 };
76 
77 #if defined(__clang__)
78 #pragma clang diagnostic pop
79 #endif
80 
81 /*
82  * use ANDROID_SINGLETON_STATIC_INSTANCE(TYPE) in your implementation file
83  * (eg: <TYPE>.cpp) to create the static instance of Singleton<>'s attributes,
84  * and avoid to have a copy of them in each compilation units Singleton<TYPE>
85  * is used.
86  * NOTE: we use a version of Mutex ctor that takes a parameter, because
87  * for some unknown reason using the default ctor doesn't emit the variable!
88  */
89 
90 #define ANDROID_SINGLETON_STATIC_INSTANCE(TYPE)                 \
91     template<> ::android::Mutex  \
92         (::android::Singleton< TYPE >::sLock)(::android::Mutex::PRIVATE);  \
93     template<> TYPE* ::android::Singleton< TYPE >::sInstance(nullptr);  /* NOLINT */ \
94     template class ::android::Singleton< TYPE >;
95 
96 
97 // ---------------------------------------------------------------------------
98 }  // namespace android
99 
100 #endif // ANDROID_UTILS_SINGLETON_H
101 
102