主备切换之State模式实现

最近项目中需要实现一个主备切换的功能，通过分析可以得出也就两个状态的切换，使用if/switch之类的语句可以轻松搞定，但是为了学习并实践State模式，这里采取了一个State模式的实现：

// HAState.h: interface for the HAState class. // // #if !defined(AFX_HASTATE_H__410262B3_3FEB_44B3_BFA7_04C4BEBCE636__INCLUDED_) #define AFX_HASTATE_H__410262B3_3FEB_44B3_BFA7_04C4BEBCE636__INCLUDED_ #if _MSC_VER > 1000 #pragma once #endif // _MSC_VER > 1000 #include <iostream> class HASwitch; enum HASTATE { STANDBY, PRIMARY, FAILURE }; class HAState { public: HAState(); virtual ~HAState(); virtual HASTATE getState(); virtual bool standby2primary( HASwitch* pSwitch ) = 0; virtual bool primary2standby( HASwitch* pSwitch ) = 0; protected: void changeState( HASwitch* pSwitch, HAState* pNewState ); protected: HASTATE m_euState; }; #endif // !defined(AFX_HASTATE_H__410262B3_3FEB_44B3_BFA7_04C4BEBCE636__INCLUDED_)

// HAState.cpp: implementation of the HAState class. // // #include "HAState.h" #include "HASwitch.h" // // Construction/Destruction // HAState::HAState():m_euState( FAILURE ) { std::cout << "Call " << __FUNCTION__ << std::endl; } HAState::~HAState() { std::cout << "Call " << __FUNCTION__ << std::endl; } void HAState::changeState( HASwitch* pSwitch, HAState* pNewState ) { std::cout << "Call " << __FUNCTION__ << std::endl; pSwitch->changeState( pNewState ); } HASTATE HAState::getState() { std::cout << "Call " << __FUNCTION__ << std::endl; return m_euState; }

// PrimaryState.h: interface for the PrimaryState class. // // #if !defined(AFX_PRIMARYSTATE_H__DFA509B1_9344_4750_A582_5637A65DF2A8__INCLUDED_) #define AFX_PRIMARYSTATE_H__DFA509B1_9344_4750_A582_5637A65DF2A8__INCLUDED_ #if _MSC_VER > 1000 #pragma once #endif // _MSC_VER > 1000 #include <boost/noncopyable.hpp> #include "HAState.h" class PrimaryState : public HAState, public boost::noncopyable { public: PrimaryState(); virtual ~PrimaryState(); static PrimaryState& instance(); virtual bool standby2primary( HASwitch* pSwitch ) ; virtual bool primary2standby( HASwitch* pSwitch ) ; private: static PrimaryState s_Instance; }; #endif // !defined(AFX_PRIMARYSTATE_H__DFA509B1_9344_4750_A582_5637A65DF2A8__INCLUDED_)

// PrimaryState.cpp: implementation of the PrimaryState class. // // #include "PrimaryState.h" #include "StandbyState.h" #include "HASwitch.h" // // Construction/Destruction // PrimaryState PrimaryState::s_Instance; PrimaryState::PrimaryState() { std::cout << "Call " << __FUNCTION__ << std::endl; m_euState = PRIMARY; } PrimaryState::~PrimaryState() { std::cout << "Call " << __FUNCTION__ << std::endl; } bool PrimaryState::standby2primary( HASwitch* pSwitch ) { std::cout << "Call " << __FUNCTION__ << std::endl; std::cout << "Current state is already primary" << std::endl; return true; } bool PrimaryState::primary2standby( HASwitch* pSwitch ) { std::cout << "Call " << __FUNCTION__ << std::endl; std::cout << "Begin switch to standby..." << std::endl; std::cout << "Do something" << std::endl; changeState( pSwitch, &StandbyState::instance() ); std::cout << "End switch to standby..." << std::endl; return true; } PrimaryState& PrimaryState::instance() { std::cout << "Call " << __FUNCTION__ << std::endl; return s_Instance; }

// StandbyState.h: interface for the StandbyState class. // // #if !defined(AFX_STANDBYSTATE_H__028C47F8_1A92_4854_A93D_2AECB6A17DF6__INCLUDED_) #define AFX_STANDBYSTATE_H__028C47F8_1A92_4854_A93D_2AECB6A17DF6__INCLUDED_ #if _MSC_VER > 1000 #pragma once #endif // _MSC_VER > 1000 #include <boost/noncopyable.hpp> #include "HAState.h" class StandbyState : public HAState, public boost::noncopyable { public: StandbyState(); virtual ~StandbyState(); static StandbyState& instance(); virtual bool standby2primary( HASwitch* pSwitch ) ; virtual bool primary2standby( HASwitch* pSwitch ) ; private: static StandbyState s_Instance; }; #endif // !defined(AFX_STANDBYSTATE_H__028C47F8_1A92_4854_A93D_2AECB6A17DF6__INCLUDED_)

// StandbyState.cpp: implementation of the StandbyState class. // // #include "StandbyState.h" #include "PrimaryState.h" #include "HASwitch.h" // // Construction/Destruction // StandbyState StandbyState::s_Instance; StandbyState::StandbyState() { std::cout << "Call " << __FUNCTION__ << std::endl; m_euState = STANDBY; } StandbyState::~StandbyState() { std::cout << "Call " << __FUNCTION__ << std::endl; } bool StandbyState::standby2primary( HASwitch* pSwitch ) { std::cout << "Call " << __FUNCTION__ << std::endl; std::cout << "Begin switch to primary..." << std::endl; std::cout << "Do something" << std::endl; changeState( pSwitch, &PrimaryState::instance() ); std::cout << "End switch to primary..." << std::endl; return true; } bool StandbyState::primary2standby( HASwitch* pSwitch ) { std::cout << "Call " << __FUNCTION__ << std::endl; std::cout << "Current state is already standby" << std::endl; return true; } StandbyState& StandbyState::instance() { std::cout << "Call " << __FUNCTION__ << std::endl; return s_Instance; }

// HASwitch.h: interface for the HASwitch class. // // #if !defined(AFX_HASWITCH_H__AC109E28_51E4_46AE_BC07_9E93FA747B65__INCLUDED_) #define AFX_HASWITCH_H__AC109E28_51E4_46AE_BC07_9E93FA747B65__INCLUDED_ #if _MSC_VER > 1000 #pragma once #endif // _MSC_VER > 1000 #include <boost/noncopyable.hpp> #include "HAState.h" class HASwitch : public boost::noncopyable { friend class HAState; public: HASwitch(); virtual ~HASwitch(); static HASwitch& instance(); HASTATE getState() const; bool standby2primary(); bool primary2standby(); private: void changeState( HAState* pNewState ); private: static HASwitch g_Instance; HAState* m_pCurState; }; #endif // !defined(AFX_HASWITCH_H__AC109E28_51E4_46AE_BC07_9E93FA747B65__INCLUDED_)

// HASwitch.cpp: implementation of the HASwitch class. // // #include "HASwitch.h" #include "HAState.h" #include "PrimaryState.h" #include "StandbyState.h" // // Construction/Destruction // HASwitch HASwitch::g_Instance; HASwitch::HASwitch() { m_pCurState = &StandbyState::instance(); std::cout << "Call " << __FUNCTION__ << std::endl; } HASwitch::~HASwitch() { std::cout << "Call " << __FUNCTION__ << std::endl; } HASTATE HASwitch::getState() const { std::cout << "Call " << __FUNCTION__ << std::endl; return m_pCurState->getState(); } bool HASwitch::standby2primary() { std::cout << "Call " << __FUNCTION__ << std::endl; return m_pCurState->standby2primary(this); } bool HASwitch::primary2standby() { std::cout << "Call " << __FUNCTION__ << std::endl; return m_pCurState->primary2standby(this); } void HASwitch::changeState( HAState* pNewState ) { std::cout << "Call " << __FUNCTION__ << std::endl; m_pCurState = pNewState; } HASwitch& HASwitch::instance() { return g_Instance; }

测试代码：

#include <iostream> #include <assert.h> #include "HASwitch.h" int main(int argc , char ** argv) { assert( HASwitch::instance().getState() == STANDBY ); HASwitch::instance().standby2primary(); assert( HASwitch::instance().getState() == PRIMARY ); HASwitch::instance().primary2standby(); assert( HASwitch::instance().getState() == STANDBY ); return 0; }