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commonlibrary/c_utils/base/include/singleton.h

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+/*
+ * Copyright (c) 2021 Huawei Device Co., Ltd.
+ * 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 UTILS_BASE_SINGLETON_H
+#define UTILS_BASE_SINGLETON_H
+
+#include "nocopyable.h"
+#include <mutex>
+#include <memory>
+
+namespace OHOS {
+
+/**
+ * The purpose of the following macro definitions is to reduce the need
+ * to write repetitive code when defining singleton classes on the client side.
+ *
+ * Taking DelayedSingleton as an example, when declaring the target class as a
+ * singleton, add the DECLARE_DELAYED_SINGLETON (class_name) to the class
+ * declaration. When using the target singleton, call
+ * class_name::GetInstance()->.
+ */
+
+/**
+ * @brief Sets `MyClass` as a `DelayedSingleton`.
+ *
+ * A `MyClass` object can be obtained by calling
+ * `DelayedSingleton<MyClass>::GetInstance()`.
+ *
+ * @param MyClass Target class to be set as a singleton.
+ *
+ * @note This macro definition should be used in the body of a class definition.
+ */
+#define DECLARE_DELAYED_SINGLETON(MyClass)\
+public:\
+    ~MyClass();\
+private:\
+    friend DelayedSingleton<MyClass>;\
+    MyClass();
+
+/**
+ * @brief Sets `MyClass` as a `DelayedRefSingleton`.
+ *
+ * A `MyClass` object can be obtained by calling
+ * `DelayedRefSingleton<MyClass>::GetInstance()`.
+ *
+ * @param MyClass Target class to be set as a singleton.
+ *
+ * @note This macro definition should be used in the body of a class definition.
+ */
+#define DECLARE_DELAYED_REF_SINGLETON(MyClass)\
+private:\
+    friend DelayedRefSingleton<MyClass>;\
+    ~MyClass();\
+    MyClass();
+
+/**
+ * @brief Sets `MyClass` as a `Singleton`.
+ *
+ * A `MyClass` object can be obtained by calling
+ * `Singleton<MyClass>::GetInstance()`.
+ *
+ * @param MyClass Target class to be set as a singleton.
+ *
+ * @note This macro definition should be used in the body of a class definition.
+ */
+#define DECLARE_SINGLETON(MyClass)\
+private:\
+    friend Singleton<MyClass>;\
+    MyClass& operator=(const MyClass&) = delete;\
+    MyClass(const MyClass&) = delete;\
+    MyClass();\
+    ~MyClass();
+
+/**
+ * @brief DelayedSingleton is a thread-safe, memory-safe lazy initialized
+ * singleton (with smart pointer and lock).
+ */
+template<typename T>
+class DelayedSingleton : public NoCopyable {
+public:
+    /**
+     * @brief Creates a unique instance object.
+     *
+     * Use a smart pointer to manage resources. If all shared_ptrs are
+     * destroyed, the new object will also be deleted. This avoids memory leaks.
+     * A lock is added only when the pointer is empty, so as to avoid locking
+     * every time `GetInstance()` is called, reducing overhead of the lock.
+     */
+    static std::shared_ptr<T> GetInstance();
+    /**
+     * @brief Releases the ownership of managed object of the smart pointer.
+     *
+     * @note After this API is called successfully, 'GetInstance()' will create
+     * a new object. If the old object has an external 'std::shared_ptr'
+     * reference, you need to release it to maintain a singleton.
+     */
+    static void DestroyInstance();
+
+private:
+    static std::shared_ptr<T> instance_; // Record the created DelayedSingleton instance.
+    static std::mutex mutex_; // Mutex, which guarantees that only one thread is accessing a common resource at any time.
+};
+
+template<typename T>
+std::shared_ptr<T> DelayedSingleton<T>::instance_ = nullptr;
+
+template<typename T>
+std::mutex DelayedSingleton<T>::mutex_;
+
+template<typename T>
+std::shared_ptr<T> DelayedSingleton<T>::GetInstance()
+{
+    if (instance_ == nullptr) {
+        std::lock_guard<std::mutex> lock(mutex_);
+        if (instance_ == nullptr) {
+            std::shared_ptr<T> temp(new (std::nothrow) T);
+            instance_ = temp;
+        }
+    }
+
+    return instance_;
+}
+
+template<typename T>
+void DelayedSingleton<T>::DestroyInstance()
+{
+    std::lock_guard<std::mutex> lock(mutex_);
+    if (instance_ != nullptr) {
+        instance_.reset();
+        instance_ = nullptr;
+    }
+}
+
+/**
+ * @brief DelayedRefSingleton is a thread-safe, lazy initialized
+ * singleton (with ordinary pointer and lock).
+ */
+template<typename T>
+class DelayedRefSingleton : public NoCopyable {
+public:
+    /**
+     * @brief Creates a unique instance object.
+     *
+     * Pointer is used in the implementation, and the return value is a
+     * reference. It points to an instance that has a lifetime managed by
+     * the non-user code.
+     *
+     * @note The instance may not have been created at a certain point in time,
+     * or it may have been deleted, and therefore it is not possible to
+     * prohibit use of the delete keyword to destroy the object in advance.
+     */
+    static T& GetInstance();
+
+private:
+    static T* instance_; // Record the DelayedRefSingleton instance created.
+    static std::mutex mutex_;
+};
+
+template<typename T>
+T* DelayedRefSingleton<T>::instance_ = nullptr;
+
+template<typename T>
+std::mutex DelayedRefSingleton<T>::mutex_;
+
+template<typename T>
+T& DelayedRefSingleton<T>::GetInstance()
+{
+    if (instance_ == nullptr) {
+        std::lock_guard<std::mutex> lock(mutex_);
+        if (instance_ == nullptr) {
+            instance_ = new T();
+        }
+    }
+
+    return *instance_;
+}
+
+/**
+ * @brief Singleton is a normally initialized singleton (without pointers and
+ * locks).
+ */
+template<typename T>
+class Singleton : public NoCopyable {
+public:
+
+    /**
+     * @brief Gets a singleton instance object.
+     */
+    static T& GetInstance() { return instance_; }
+
+private:
+    static T instance_;
+};
+
+template<typename T>
+T Singleton<T>::instance_;
+} // namespace OHOS
+
+#endif