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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 #include <cutils/compiler.h>
     24 
     25 namespace android {
     26 // ---------------------------------------------------------------------------
     27 
     28 template <typename TYPE>
     29 class ANDROID_API Singleton
     30 {
     31 public:
     32     static TYPE& getInstance() {
     33         Mutex::Autolock _l(sLock);
     34         TYPE* instance = sInstance;
     35         if (instance == 0) {
     36             instance = new TYPE();
     37             sInstance = instance;
     38         }
     39         return *instance;
     40     }
     41 
     42     static bool hasInstance() {
     43         Mutex::Autolock _l(sLock);
     44         return sInstance != 0;
     45     }
     46 
     47 protected:
     48     ~Singleton() { };
     49     Singleton() { };
     50 
     51 private:
     52     Singleton(const Singleton&);
     53     Singleton& operator = (const Singleton&);
     54     static Mutex sLock;
     55     static TYPE* sInstance;
     56 };
     57 
     58 /*
     59  * use ANDROID_SINGLETON_STATIC_INSTANCE(TYPE) in your implementation file
     60  * (eg: <TYPE>.cpp) to create the static instance of Singleton<>'s attributes,
     61  * and avoid to have a copy of them in each compilation units Singleton<TYPE>
     62  * is used.
     63  * NOTE: we use a version of Mutex ctor that takes a parameter, because
     64  * for some unknown reason using the default ctor doesn't emit the variable!
     65  */
     66 
     67 #define ANDROID_SINGLETON_STATIC_INSTANCE(TYPE)                 \
     68     template<> Mutex Singleton< TYPE >::sLock(Mutex::PRIVATE);  \
     69     template<> TYPE* Singleton< TYPE >::sInstance(0);           \
     70     template class Singleton< TYPE >;
     71 
     72 
     73 // ---------------------------------------------------------------------------
     74 }; // namespace android
     75 
     76 #endif // ANDROID_UTILS_SINGLETON_H
     77 
     78