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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 
     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 template <typename TYPE>
     43 class ANDROID_API Singleton
     44 {
     45 public:
     46     static TYPE& getInstance() {
     47         Mutex::Autolock _l(sLock);
     48         TYPE* instance = sInstance;
     49         if (instance == 0) {
     50             instance = new TYPE();
     51             sInstance = instance;
     52         }
     53         return *instance;
     54     }
     55 
     56     static bool hasInstance() {
     57         Mutex::Autolock _l(sLock);
     58         return sInstance != 0;
     59     }
     60 
     61 protected:
     62     ~Singleton() { }
     63     Singleton() { }
     64 
     65 private:
     66     Singleton(const Singleton&);
     67     Singleton& operator = (const Singleton&);
     68     static Mutex sLock;
     69     static TYPE* sInstance;
     70 };
     71 
     72 #if defined(__clang__)
     73 #pragma clang diagnostic pop
     74 #endif
     75 
     76 /*
     77  * use ANDROID_SINGLETON_STATIC_INSTANCE(TYPE) in your implementation file
     78  * (eg: <TYPE>.cpp) to create the static instance of Singleton<>'s attributes,
     79  * and avoid to have a copy of them in each compilation units Singleton<TYPE>
     80  * is used.
     81  * NOTE: we use a version of Mutex ctor that takes a parameter, because
     82  * for some unknown reason using the default ctor doesn't emit the variable!
     83  */
     84 
     85 #define ANDROID_SINGLETON_STATIC_INSTANCE(TYPE)                 \
     86     template<> ::android::Mutex  \
     87         (::android::Singleton< TYPE >::sLock)(::android::Mutex::PRIVATE);  \
     88     template<> TYPE* ::android::Singleton< TYPE >::sInstance(0);  \
     89     template class ::android::Singleton< TYPE >;
     90 
     91 
     92 // ---------------------------------------------------------------------------
     93 }; // namespace android
     94 
     95 #endif // ANDROID_UTILS_SINGLETON_H
     96 
     97