SingletonPtr.h

00001 
00002 /** \addtogroup platform */
00003 /** @{*/
00004 /* mbed Microcontroller Library
00005  * Copyright (c) 2006-2013 ARM Limited
00006  *
00007  * Licensed under the Apache License, Version 2.0 (the "License");
00008  * you may not use this file except in compliance with the License.
00009  * You may obtain a copy of the License at
00010  *
00011  *     http://www.apache.org/licenses/LICENSE-2.0
00012  *
00013  * Unless required by applicable law or agreed to in writing, software
00014  * distributed under the License is distributed on an "AS IS" BASIS,
00015  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00016  * See the License for the specific language governing permissions and
00017  * limitations under the License.
00018  */
00019 #ifndef SINGLETONPTR_H
00020 #define SINGLETONPTR_H
00021 
00022 #include <stdint.h>
00023 #include <new>
00024 #include "platform/mbed_assert.h"
00025 #ifdef MBED_CONF_RTOS_PRESENT
00026 #include "cmsis_os.h"
00027 #endif
00028 
00029 #ifdef MBED_CONF_RTOS_PRESENT
00030 extern osMutexId singleton_mutex_id;
00031 #endif
00032 
00033 /** Lock the singleton mutex
00034  *
00035  * This function is typically used to provide
00036  * exclusive access when initializing a
00037  * global object.
00038  */
00039 inline static void singleton_lock(void)
00040 {
00041 #ifdef MBED_CONF_RTOS_PRESENT
00042     osMutexWait(singleton_mutex_id, osWaitForever);
00043 #endif
00044 }
00045 
00046 /** Unlock the singleton mutex
00047  *
00048  * This function is typically used to provide
00049  * exclusive access when initializing a
00050  * global object.
00051  */
00052 inline static void singleton_unlock(void)
00053 {
00054 #ifdef MBED_CONF_RTOS_PRESENT
00055     osMutexRelease (singleton_mutex_id);
00056 #endif
00057 }
00058 
00059 /** Utility class for creating an using a singleton
00060  *
00061  * @Note Synchronization level: Thread safe
00062  *
00063  * @Note: This class must only be used in a static context -
00064  * this class must never be allocated or created on the
00065  * stack.
00066  *
00067  * @Note: This class is lazily initialized on first use.
00068  * This class is a POD type so if it is not used it will
00069  * be garbage collected.
00070  */
00071 template <class T>
00072 struct SingletonPtr {
00073 
00074     /** Get a pointer to the underlying singleton
00075      *
00076      * @returns
00077      *   A pointer to the singleton
00078      */
00079     T* get() {
00080         if (NULL == _ptr) {
00081             singleton_lock();
00082             if (NULL == _ptr) {
00083                 _ptr = new (_data) T();
00084             }
00085             singleton_unlock();
00086         }
00087         // _ptr was not zero initialized or was
00088         // corrupted if this assert is hit
00089         MBED_ASSERT(_ptr == (T *)&_data);
00090         return _ptr;
00091     }
00092 
00093     /** Get a pointer to the underlying singleton
00094      *
00095      * @returns
00096      *   A pointer to the singleton
00097      */
00098     T* operator->() {
00099         return get();
00100     }
00101 
00102     // This is zero initialized when in global scope
00103     T *_ptr;
00104     // Force data to be 4 byte aligned
00105     uint32_t _data[(sizeof(T) + sizeof(uint32_t) - 1) / sizeof(uint32_t)];
00106 };
00107 
00108 #endif
00109 
00110 /** @}*/