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      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 
     24 namespace android {
     25 // ---------------------------------------------------------------------------
     26 
     27 template <typename TYPE>
     28 class Singleton
     29 {
     30 public:
     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 
     46 protected:
     47     ~Singleton() { };
     48     Singleton() { };
     49 
     50 private:
     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