设计模式之 单例模式_单例模式在嵌入式中的应用

介绍

几个重点：

• 构造函数为private
• 提供一个获取单例对象指针的函数
• 一个静态指针成员存储单例对象

注意：

• 获取单例对象也可以获取对象引用，但要注意拷贝构造函数和赋值运算符
• 如果有多线程访问单例，需要注意线程同步

UML类图：

简单示例：

懒汉和饿汉模式：

#ifndef SIMPLE_SINGLETON_H
#define SIMPLE_SINGLETON_H
 
#include <iostream>
using namespace std;
 
/**
 * @brief The LazySingleton class
 * 懒汉模式
 */
class LazySingleton
{
public:
    static LazySingleton *getInstance()
    {
        if( m_instance == nullptr)
            m_instance = new LazySingleton;
 
        return  m_instance;
    }
 
    static void freeInstance()
    {
        if( m_instance != nullptr )
            delete  m_instance;
 
        m_instance = nullptr;
    }
private:
    LazySingleton()
    {
        cout<<" LazySingleton 构造函数执行"<<endl;
    }
    static LazySingleton *m_instance ;
};
LazySingleton *LazySingleton::m_instance = nullptr;
 
 
/**
 * @brief The HungrySingleton class
 * 饿汉模式，一般用不到
 */
class  HungrySingleton
{
public:
    static HungrySingleton *getInstance()
    {
        if( m_instance == nullptr)
            m_instance = new HungrySingleton;
 
        return  m_instance;
    }
 
    static void freeInstance()
    {
        if( m_instance != nullptr )
            delete  m_instance;
 
        m_instance = nullptr;
    }
private:
    HungrySingleton()
    {
        cout<<" HungrySingleton 构造函数执行"<<endl;
    }
    static HungrySingleton *m_instance ;
};
HungrySingleton *HungrySingleton::m_instance = new HungrySingleton;
 
#endif // SIMPLE_SINGLETON_H

懒汉线程安全模式：

#ifndef THREAD_SINGLETON_H
#define THREAD_SINGLETON_H
 
#include <iostream>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
using namespace std;
 
 
void printids(const char *s)
{
    pid_t pid;
    pthread_t tid;
    pid = getpid();
    tid = pthread_self();
    printf("%s pid %u tid %u (0x%x)\n", s, (unsigned int) pid,
           (unsigned int) tid, (unsigned int) tid);
}
 
 
 
 
class LazySingleton
{
public:
    static LazySingleton *getInstance()
    {
 
//        if( m_instance == nullptr)
//        {
//            m_count++;
//            m_instance = new LazySingleton;
//        }
 
        if( m_instance == nullptr)
        {
            pthread_mutex_lock(&m_mutex_lock);
 
             if( m_instance == nullptr)
             {
                 m_count++;
                 m_instance = new LazySingleton;
             }
 
            pthread_mutex_unlock(&m_mutex_lock);
        }
 
 
 
        return  m_instance;
    }
 
    static void freeInstance()
    {
        if( m_instance != nullptr )
            delete  m_instance;
 
        pthread_mutex_destroy(&m_mutex_lock);
        m_instance = nullptr;
    }
 
    void showMessage()
    {
        cout<<"LazySingleton message!"<<endl;
    }
private:
    LazySingleton()
    {
 
 
        cout<<" LazySingleton 构造函数执行开始"<<endl;
        sleep(2);
        cout<<" LazySingleton 构造函数执行 ["<<m_count<<"] 次"<<endl;
    }
    static LazySingleton *m_instance ;
    static int m_count;
    static pthread_mutex_t m_mutex_lock;
};
LazySingleton *LazySingleton::m_instance = nullptr;
int LazySingleton::m_count = 0;
pthread_mutex_t LazySingleton::m_mutex_lock = PTHREAD_MUTEX_INITIALIZER;
 
 
void *thr_fn(void *arg)
{
   // printids("new thread: ");
 
    LazySingleton::getInstance()->showMessage();
    return nullptr;
}
 
#endif // THREAD_SINGLETON_H

线程安全，调用方式： 

 printids("main thread:");
    int err;
    pthread_t ntid[3];
    for (int i=0 ; i<3 ; i++) {
        err = pthread_create(&ntid[i], NULL, thr_fn, NULL);
        if (err != 0)
            printf("can't create thread: %s\n", strerror(err));
 
 
    }
    for (int i=0; i < 3 ; i++) {
        pthread_join(ntid[i],NULL);
    }

内部静态类（懒汉）方式：

 
class  StackSingleton
{
public:
    static StackSingleton *getInstance()
    {
        //内部静态实例的懒汉模式
        pthread_mutex_lock(&m_mutex_lock);
        static StackSingleton _instance ;
        pthread_mutex_unlock(&m_mutex_lock);
        return  &_instance;
    }
 
    void printS()
    {
        cout<<"栈方式的单例模式..."<<endl;
    }
 
 
private:
    StackSingleton()
    {
        cout<<" StackSingleton 构造函数执行"<<endl;
    }
 
    static pthread_mutex_t m_mutex_lock;
 
};
pthread_mutex_t StackSingleton::m_mutex_lock = PTHREAD_MUTEX_INITIALIZER;