学习设计模式系列之一：单例模式

学习一下C++的单例模式(Singleton)实现方法，顺便练习一下多线程编程。

代码：

#include <stdlib.h>
#include <windows.h>

/***
* @author:zanzan101
*/

class A
{
public:
    static A* get_instance()
    {
        while(WAIT_OBJECT_0 != WaitForSingleObject(mutex, 0))
            Sleep(100);    // 设置100毫秒的相应时间

        if(NULL == singleton)
            singleton = new A();

        ReleaseMutex(mutex);
        return singleton;
    }
    void do_something()
    {
        printf("The data is %d
", get_data());
    }
    void set_data(const int& n)
    {
        data = n;
    }
    const int get_data()
    {
        return data;
    }
protected:
private:
    A():data(0){}
    static A* singleton;
    static HANDLE mutex;
    int data;
};
A* A::singleton = NULL;
HANDLE A::mutex = CreateMutex(NULL, NULL, "A");

struct PARA
{
    int a;
    int b;
    int c;
};
void __stdcall runnable(PARA* para)
{
    A* ptr = A::get_instance();

    // 下面这三个语句没用进行同步管理，可以从输出结果来感受多线程带来的混乱
    ptr->set_data(para->a);
    // 根据输出结果可知，printf不能被多线程中断，而cout可以被中断
    printf("%d, %d, %d, %d
", para->a, para->b, para->c, ptr->get_data());
    ptr->do_something();
}

// 关于C++的一种函数指针的类型转换：reinterpret_cast，高大上～
typedef DWORD  (__stdcall * func_callback)(void* para);
func_callback callback_func = reinterpret_cast<DWORD(__stdcall*)(void*)>(runnable);

int main()
{
    // 关于单例模式

    A* a = A::get_instance();
    a->set_data(10);
    printf(">> 输出a:
");
    a->do_something();
    A* b = A::get_instance();
    printf(">> 输出b:
");
    b->do_something();
    b->set_data(20);
    printf(">> 输出b:
");
    b->do_something();
    b->set_data(20);
    printf(">> 输出a:
");
    a->do_something();

    if(a->get_data() == b->get_data())
        printf(">> a和b指向了同一个对象！
");

    // 关于多线程

    PARA para[10];
    for(int i = 0; i < 10; i++)
        para[i].a = para[i].b = para[i].c = i;

    HANDLE thread[10];
    for(int i = 0; i < 10; i++)
        thread[i] = CreateThread(NULL, 1024, callback_func, (void*)&para[i], 0, 0);
    
    Sleep(2000);

    for(int i = 0; i < 10; i++)
    {
        TerminateThread(thread[i], 0);
        CloseHandle(thread[i]);
    }

    system("pause");
    return 0;
}

输出结果：

>> 输出a:
The data is 10
>> 输出b:
The data is 10
>> 输出b:
The data is 20
>> 输出a:
The data is 20
>> a和b指向了同一个对象！
0, 0, 0, 0
1, 1, 1, 1
The data is 1
The data is 1
3, 3, 3, 3
The data is 2
4, 4, 4, 4
2, 2, 2, 2
5, 5, 5, 5
The data is 5
8, 8, 8, 8
6, 6, 6, 6
The data is 5
7, 7, 7, 7
The data is 5
9, 9, 9, 9
The data is 9
The data is 9
The data is 9
The data is 9
请按任意键继续. . .