Mbed OS Reference | SharedPtr.h Source File

 /* mbed Microcontroller Library
  * Copyright (c) 2006-2018 ARM Limited
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 
 #ifndef __SHAREDPTR_H__
 #define __SHAREDPTR_H__
 
 #include <stdlib.h>
 
 #include <stdint.h>
 #include <stddef.h>
 
 #include "platform/mbed_atomic.h"
 
 namespace mbed {
 
 /** Shared pointer class.
   *
   * A shared pointer is a "smart" pointer that retains ownership of an object using
   * reference counting across all smart pointers referencing that object.
   *
   * @code
   * #include "platform/SharedPtr.h"
   *
   * void test() {
   *     struct MyStruct { int a; };
   *
   *     // Create shared pointer
   *     SharedPtr<MyStruct> ptr( new MyStruct );
   *
   *     // Increase reference count
   *     SharedPtr<MyStruct> ptr2( ptr );
   *
   *     ptr = nullptr; // Reference to the struct instance is still held by ptr2
   *
   *     ptr2 = nullptr; // The raw pointer is freed
   * }
   * @endcode
   *
   *
   * It is similar to the std::shared_ptr class introduced in C++11;
   * however, this is not a compatible implementation (no weak pointer, no make_shared, no custom deleters and so on.)
   *
   * Usage: SharedPtr<Class> ptr(new Class())
   *
   * When ptr is passed around by value, the copy constructor and
   * destructor manages the reference count of the raw pointer.
   * If the counter reaches zero, delete is called on the raw pointer.
   *
   * To avoid loops, use "weak" references by calling the original
   * pointer directly through ptr.get().
   */
 
 template <class T>
 class SharedPtr {
 public:
     /**
      * @brief Create empty SharedPtr not pointing to anything.
      * @details Used for variable declaration.
      */
     constexpr SharedPtr(): _ptr(), _counter()
     {
     }
 
     /**
      * @brief Create empty SharedPtr not pointing to anything.
      */
     constexpr SharedPtr(std::nullptr_t) : SharedPtr()
     {
     }
 
     /**
      * @brief Create new SharedPtr
      * @param ptr Pointer to take control over
      */
     SharedPtr(T *ptr): _ptr(ptr), _counter()
     {
         // Allocate counter on the heap, so it can be shared
         if (_ptr != nullptr) {
             _counter = new uint32_t(1);
         }
     }
 
     /**
      * @brief Destructor.
      * @details Decrement reference counter, and delete object if no longer pointed to.
      */
     ~SharedPtr()
     {
         decrement_counter();
     }
 
     /**
      * @brief Copy constructor.
      * @details Create new SharedPtr from other SharedPtr by
      *          copying pointer to original object and pointer to counter.
      * @param source Object being copied from.
      */
     SharedPtr(const SharedPtr &source): _ptr(source._ptr), _counter(source._counter)
     {
         // Increment reference counter
         if (_ptr != nullptr) {
             core_util_atomic_incr_u32(_counter, 1);
         }
     }
 
     /**
      * @brief Move constructor.
      * @details Create new SharedPtr from other SharedPtr by
      *          moving pointer to original object and pointer to counter.
      * @param source Object being copied from.
      */
     SharedPtr(SharedPtr &&source): _ptr(source._ptr), _counter(source._counter)
     {
         source._ptr = nullptr;
         source._counter = nullptr;
     }
 
     /**
      * @brief Copy assignment operator.
      * @details Cleanup previous reference and assign new pointer and counter.
      * @param source Object being assigned from.
      * @return Object being assigned.
      */
     SharedPtr operator=(const SharedPtr &source)
     {
         if (this != &source) {
             // Clean up by decrementing counter
             decrement_counter();
 
             // Assign new values
             _ptr = source.get();
             _counter = source.get_counter();
 
             // Increment new counter
             if (_ptr != nullptr) {
                 core_util_atomic_incr_u32(_counter, 1);
             }
         }
 
         return *this;
     }
 
     /**
      * @brief Move assignment operator.
      * @details Cleanup previous reference and assign new pointer and counter.
      * @param source Object being assigned from.
      * @return Object being assigned.
      */
     SharedPtr operator=(SharedPtr &&source)
     {
         if (this != &source) {
             // Clean up by decrementing counter
             decrement_counter();
 
             // Assign new values
             _ptr = source._ptr;
             _counter = source._counter;
 
             source._ptr = nullptr;
             source._counter = nullptr;
         }
 
         return *this;
     }
 
     /**
      * @brief Replaces the managed pointer with a new unmanaged pointer.
      * @param[in] ptr the new raw pointer to manage.
      */
     void reset(T *ptr)
     {
         // Clean up by decrementing counter
         decrement_counter();
 
         _ptr = ptr;
         if (ptr != nullptr) {
             // Allocate counter on the heap, so it can be shared
             _counter = new uint32_t(1);
         } else {
             _counter = nullptr;
         }
     }
 
     /**
      * @brief Replace the managed pointer with a null pointer.
      */
     void reset()
     {
         // Clean up by decrementing counter
         decrement_counter();
 
         _ptr = nullptr;
         _counter = nullptr;
     }
 
     /**
      * @brief Raw pointer accessor.
      * @details Get raw pointer to object pointed to.
      * @return Pointer.
      */
     T *get() const
     {
         return _ptr;
     }
 
     /**
      * @brief Reference count accessor.
      * @return Reference count.
      */
     uint32_t use_count() const
     {
         if (_ptr != nullptr) {
             return core_util_atomic_load_u32(_counter);
         } else {
             return 0;
         }
     }
 
     /**
      * @brief Dereference object operator.
      * @details Override to return the object pointed to.
      */
     T &operator*() const
     {
         return *_ptr;
     }
 
     /**
      * @brief Dereference object member operator.
      * @details Override to return return member in object pointed to.
      */
     T *operator->() const
     {
         return _ptr;
     }
 
     /**
      * @brief Boolean conversion operator.
      * @return Whether or not the pointer is null.
      */
     operator bool() const
     {
         return _ptr != nullptr;
     }
 
 private:
     /**
      * @brief Get pointer to reference counter.
      * @return Pointer to reference counter.
      */
     uint32_t *get_counter() const
     {
         return _counter;
     }
 
     /**
      * @brief Decrement reference counter.
      * @details If count reaches zero, free counter and delete object pointed to.
      * Does not modify our own pointers - assumption is they will be overwritten
      * or destroyed immediately afterwards.
      */
     void decrement_counter()
     {
         if (_ptr != nullptr) {
             if (core_util_atomic_decr_u32(_counter, 1) == 0) {
                 delete _counter;
                 delete _ptr;
             }
         }
     }
 
 private:
     // Pointer to shared object
     T *_ptr;
 
     // Pointer to shared reference counter
     uint32_t *_counter;
 };
 
 /** Non-member relational operators.
   */
 template <class T, class U>
 bool operator== (const SharedPtr<T> &lhs, const SharedPtr<U> &rhs)
 {
     return (lhs.get() == rhs.get());
 }
 
 template <class T, typename U>
 bool operator== (const SharedPtr<T> &lhs, U rhs)
 {
     return (lhs.get() == (T *) rhs);
 }
 
 template <class T, typename U>
 bool operator== (U lhs, const SharedPtr<T> &rhs)
 {
     return ((T *) lhs == rhs.get());
 }
 
 /** Non-member relational operators.
   */
 template <class T, class U>
 bool operator!= (const SharedPtr<T> &lhs, const SharedPtr<U> &rhs)
 {
     return (lhs.get() != rhs.get());
 }
 
 template <class T, typename U>
 bool operator!= (const SharedPtr<T> &lhs, U rhs)
 {
     return (lhs.get() != (T *) rhs);
 }
 
 template <class T, typename U>
 bool operator!= (U lhs, const SharedPtr<T> &rhs)
 {
     return ((T *) lhs != rhs.get());
 }
 
 } /* namespace mbed */
 
 #ifndef MBED_NO_GLOBAL_USING_DIRECTIVE
 using mbed::SharedPtr;
 #endif
 
 #endif // __SHAREDPTR_H__
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