Home | History | Annotate | Download | only in utils 
      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:
     51     static TYPE& getInstance() {
     52         Mutex::Autolock _l(sLock);
     53         TYPE* instance = sInstance;
     54         if (instance == 0) {
     55             instance = new TYPE();
     56             sInstance = instance;
     57         }
     58         return *instance;
     59     }
     60 
     61     static bool hasInstance() {
     62         Mutex::Autolock _l(sLock);
     63         return sInstance != 0;
     64     }
     65 
     66 protected:
     67     ~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(0);  /* NOLINT */ \
     94     template class ::android::Singleton< TYPE >;
     95 
     96 
     97 // ---------------------------------------------------------------------------
     98 }; // namespace android
     99 
    100 #endif // ANDROID_UTILS_SINGLETON_H
    101 
    102