Ice简介+Qt代码示例

1、ICE是什么？

           ICE是ZEROC的开源通信协议产品，它的全称是：The Internet Communications Engine，翻译为中文是互联网通信引擎，是一个面向对象的中间件，它封装并实现了底层的通讯逻辑，使我们能够方便的构建分布式应用程序。相对于只面向WINDOWS系统微软的.NET（以及原来的DCOM）、复杂的CORBA及性能较差的WEB SERVICE等分布式方案，ICE很好的解决了这些中间件的不足：它支持不同的系统，如WINDOWS、LINUX等，支持在多种开发语言上使用，如C++、C、JAVA、RUBY、PYTHON、VB等。服务端可以是上面提到的任何一种语言实现的，客户端也可以根据自己的实际情况选择不同的语言实现，如服务端采用C语言实现，而客户端采用JAVA语言实现等。

2: ICE的安装和示例

2.1 ICE安装

　　 ICE官网：https://zeroc.com,点击download后选择合适的平台/开发环境即可,Ubuntu18.04的安装如下图。

       

      notes: 注意ICE3.7.2与3.6.x版本差异较大，头文件不互相兼容，选用时需注意客户端/服务端ICE版本的一致性，避免代码无法编译通过。

2.2： hello world代码示例

      官网的helloworld程序，详见官网目录https://doc.zeroc.com/ice/3.7/hello-world-application

      首先创建一个slice文件Printer.ice，并将程序需要远程调用的接口写入其中。对于hello world程序，slice文件可按如下来写： 

module Demo
{
    interface Printer
    {
        void printString(string s);
    }
}

        下面我们以C++（c++11）为例，分别实现服务端和客户端。首先，我们使用slice2cpp将ice文件转换成C++可使用的.h和.cpp文件。其中.h文件中包含了我们需要远程调用的接口定义以及ICE封装，最主要的有Printer和PrinterPrx类，分别是服务端需要实现的具体对象和客户端使用的代理，其中PrinterPrx代理类中还提供了printStringAsync异步调用方法。      

slice2cpp Printer.ice                                

        服务端需要实现Printer类的接口，并创建本地创建，之后添加到ice适配器上，以便客户端远程调用。具体实现代码如下：

#include <Ice/Ice.h>
#include <Printer.h>
 
using namespace std;
using namespace Demo;
 
class PrinterI : public Printer
{
public:
    virtual void printString(string s, const Ice::Current&) override;
};
 
void 
PrinterI::printString(string s, const Ice::Current&)
{
    cout << s << endl;
}
 
int
main(int argc, char* argv[])
{
    try
    {
        Ice::CommunicatorHolder ich(argc, argv);
        auto adapter = ich->createObjectAdapterWithEndpoints("SimplePrinterAdapter", "default -h localhost -p 10000");
        auto servant = make_shared<PrinterI>();
        adapter->add(servant, Ice::stringToIdentity("SimplePrinter"));
        adapter->activate();
        ich->waitForShutdown();
    }
    catch(const std::exception& e)
    {
        cerr << e.what() << endl;
        return 1;
    }
    return 0;
}

       客户端需要创建远程对象的代理，并通过代理进行远程调用，代码如下：

#include <Ice/Ice.h>
#include <Printer.h>
#include <stdexcept>
 
using namespace std;
using namespace Demo;
 
int
main(int argc, char* argv[])
{
    try
    {
        Ice::CommunicatorHolder ich(argc, argv);
        auto base = ich->stringToProxy("SimplePrinter:default -p 10000");
        auto printer = Ice::checkedCast<PrinterPrx>(base);
        if(!printer)
        {
            throw std::runtime_error("Invalid proxy");
        }
 
        printer->printString("Hello World!");
    }
    catch(const std::exception& e)
    {
        cerr << e.what() << endl;
        return 1;
    }
    return 0;
}

       上面的demo演示了ice远程调用的基本工作方式，ICE接口的详细解释既可通过ICE官网查看，也可在安装ICE后查看相应的头文件注释。然而实际工程中我们需要对ice进行配置，处理网络异常，在服务端进行回调，穿透防火墙，进行线程调度等工作。虽然在ICE的chat demo中有介绍这些工作，然而其demo中引入了Glacier2 rooter中session的使用，而github中代码复杂度更高。相反，以上这些工作不通过Glacier2 rooter也能完美的解决，详见如下代码及注释。

完整可运行的Qt工程（可复用的ICE通信模板）可参考https://github.com/leaf-yyl/ice_template

ICE 文件： 定义了一个服务端需要提供的服务 以及一个客户端需要的回调

module Demo
{
    interface ServerService
    {
        void requireService(string ident, string s);
    }

    interface ClientCallback
    {
        void callback(string s);
    }
}

server端代码 ： 服务器端worker对象提供具体的服务， ice_manager对象负责ic模块的管理，并接收客户端请求，这些请求会在不同的ICE线程中接收到，然后通过postevent函数最终全部转发到

worker的工作线程并依序处理，如果提供的服务是线程安全的且需要高并发，那么可以去除这一步以获得高性能。相反，如果worker提供的服务不是线程安全的，或者worker中存在线程相关的资源

（例如python解释器等），则必须通过事件循环或者消息队列将ICE线程收到的客户端请求汇总到worker线程统一处理。

#include <QEvent>
#include <QObject>
#include <QCoreApplication>


#include <stdexcept>

#include <Ice/Ice.h>
#include "Printer.h"

using namespace std;

class CustomEvent : public QEvent
{
public:
    explicit CustomEvent(Type type) :QEvent(type) {

    }

    enum PMAlgoEventType {
        CustomEvent_RequireService = 0x00000001,
    };

    string m_params;
    Demo::ClientCallbackPrxPtr m_callback;
};

class ServerI : public Demo::ServerService
{
public:
    ServerI(){}

    /* Use event loop implement in QObject by Qt to post client requirements to user thread.
     * May be replaced by event loop in pure C++, handler in java and so on.
     */
    void setImplement(QObject *implement) {
        m_implement = implement;
    }

    void requireService(string ident, string s, const ::Ice::Current& current) override
    {
        /* we donot generate the client requirement here, but post it to main thread as this function is called in ice server threads.
         * When the interface is not thread safe or time-consuming, or has thread associated context like python interpreter, we must post
         * it to a constant thread managered by ourself to avoid running exceptions.
         * ident : client object identification, used to build bidirectional connection to cross firewall and local network
         * s : params used for servcie
         */
        CustomEvent *e = new CustomEvent(QEvent::Type(QEvent::User + CustomEvent::CustomEvent_RequireService));
        e->m_params   = s;
        e->m_callback = Ice::uncheckedCast<Demo::ClientCallbackPrx>(current.con->createProxy(Ice::stringToIdentity(ident)));
        QCoreApplication::postEvent(m_implement, e);
    }

private:
    QObject *m_implement;
};

class IceManager
{
public:
    IceManager() {

        /* set up global ice configurations, here we just set thread pool to 2 to avoid deadlock on ice callback,
         * other settings are configurable as the same.
         */
        Ice::PropertiesPtr props0 = Ice::createProperties();
        props0->setProperty("Ice.ThreadPool.Server.Size", "2");
        props0->setProperty("Ice.ThreadPool.Server.SizeMax", "2");
        props0->setProperty("Ice.ThreadPool.Client.Size", "2");
        props0->setProperty("Ice.ThreadPool.Client.SizeMax", "2");
        props0->setProperty("Ice.Trace.ThreadPool", "1");

        Ice::InitializationData id;
        id.properties = props0;
        m_ich = Ice::CommunicatorHolder(id);
    }

    bool setImplement(QObject *implement) {
        try {
            /* create server object and add it to ice adapter to receive client requirements.
             * The adapter identification is used for ice pack service, we donot use it now.
             * The endpoints is the location url where client can access to require service.
             * The servant identification is used to identify servant as we can add multiple servants to one adapter.
             */
            shared_ptr<ServerI> servant = make_shared<ServerI>();
            servant->setImplement(implement);
            auto adapter = m_ich->createObjectAdapterWithEndpoints("ServerAdapter", "default -h localhost -p 10000");
            adapter->add(servant, Ice::stringToIdentity("Server"));
            adapter->activate();
        } catch (const exception &e)
        {
            cout << "Failed to create ice server object, error-->%s" << e.what() << endl;
            return false;
        }

        return true;
    }

private:
    Ice::CommunicatorHolder m_ich;
};

class MainWorker : public QObject
{
public:
    MainWorker(QObject *parent = nullptr) : QObject(parent) {}

protected:

    /* Receive client requirements and deliver to associated servcie function */
    void customEvent(QEvent *e) {
        CustomEvent *event = (CustomEvent *)e;

        int type = event->type() - QEvent::User;
        if (CustomEvent::CustomEvent_RequireService == type) {
            renderService(event->m_params, event->m_callback);
        } else {
            cout << "Unrecognized event type-->" << type << "!" << endl;
        }
    }

private:
    /* a simple implement */
    void renderService(const string& s, const Demo::ClientCallbackPrxPtr& callback) {
        cout << s << endl;
        callback->callback("Requirement done!");
    }
};

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    MainWorker worker(&a);

    IceManager ice_manager;
    ice_manager.setImplement(&worker);

    return a.exec();
}

client端 头文件代码：客户端基本上与服务端类似， 但是多了一个主动发起请求的IceRequirer类，并在IceRequirer中设置链接参数等创建保活的ICE链接，达到与服务端的双向通信，具体原因

见代码注释。

#ifndef HELPER_H
#define HELPER_H


#include <QTimer>
#include <QEvent>
#include <QObject>
#include <QThread>
#include <QCoreApplication>


#include <stdexcept>

#include <Ice/Ice.h>
#include "Printer.h"

using namespace std;

/* custom event used for event loop */
class CustomEvent : public QEvent
{
public:
    explicit CustomEvent(Type type) :QEvent(type) {}

    enum PMAlgoEventType {
        CustomEvent_RequireCallback = 0x00000001,
    };

    string m_params;
};

class ClientI : public Demo::ClientCallback
{
public:
    ClientI(){}

    /* Use event loop implement in QObject by Qt to post client requirements to user thread.
     * May be replaced by event loop in pure C++, handler in java and so on.
     */
    void setImplement(QObject *implement) {
        m_server_implement = implement;
    }

    void callback(string s, const ::Ice::Current&) override
    {
        /* we donot generate the client requirement here, but post it to main thread as this function is called in ice server threads.
         * When the interface is not thread safe or time-consuming, or has thread associated context like python interpreter, we must post
         * it to a constant thread managered by ourself to avoid running exceptions.
         * s : params used for servcie
         */
        CustomEvent *e = new CustomEvent(QEvent::Type(QEvent::User + CustomEvent::CustomEvent_RequireCallback));
        e->m_params    = s;
        QCoreApplication::postEvent(m_server_implement, e);
    }

private:
    QObject *m_server_implement;
};

class ServerRequirer : public QObject
{
    Q_OBJECT
public:
    explicit ServerRequirer(const Ice::CommunicatorHolder &ich, const Ice::ObjectAdapterPtr &adapter, const string& ident) {
        m_ic        = ich.communicator();
        m_adapter   = adapter;
        m_ident     = ident;
    }

public slots:
    void slot_requireServcie(const string& s) {
        if (nullptr == m_server_prx.get()) {
            /* connection is not established, try to establish connection first */
            try {
                auto base = m_ic->stringToProxy("Server:default -h localhost -p 10000");
                m_server_prx = Ice::checkedCast<Demo::ServerServicePrx>(base);
                if(nullptr != m_server_prx.get())
                {
                    /* set up eseential configurations on Ice connection to keep this connection alive */
                    m_server_prx->ice_getConnection()->setACM(Ice::nullopt, Ice::ACMClose::CloseOff, Ice::ACMHeartbeat::HeartbeatAlways);
                    m_server_prx->ice_getConnection()->setAdapter(m_adapter);
                }
            }
            catch(const exception& e)
            {
                cerr << e.what() << endl;
            }
        }

        if (nullptr != m_server_prx.get()) {
            try {
                /* require remote object call via object proxy */
                m_server_prx->requireService(m_ident, s);
            }
            catch(const exception& e)
            {
                /* connection lost, reset it and re-establish it on next call */
                cerr << e.what() << endl;
                m_server_prx.reset();
            }
        }
    }

private:
    string m_ident;
    Ice::CommunicatorPtr      m_ic;
    Ice::ObjectAdapterPtr     m_adapter;
    Demo::ServerServicePrxPtr m_server_prx;
};

class IceManager : public QThread
{
    Q_OBJECT
public:
    /* Craete ice global communicator and manager ice requirement.
     * Server requirements are posted in seperate thread as they may be time-consuming
     * Local object that implements callback is identified through bidirectional connection instead of
     * creating a new connection fron server to client, as client may be defensed behind firewall or local network.
     */
    IceManager() {

        /* register qt meta type */
        qRegisterMetaType<string>("string");

        /* set up global ice configurations, here we just set thread pool to 2 to avoid deadlock on ice callback,
         * other settings are configurable as the same.
         */
        Ice::PropertiesPtr props0 = Ice::createProperties();
        props0->setProperty("Ice.ThreadPool.Server.Size", "2");
        props0->setProperty("Ice.ThreadPool.Server.SizeMax", "2");
        props0->setProperty("Ice.ThreadPool.Client.Size", "2");
        props0->setProperty("Ice.ThreadPool.Client.SizeMax", "2");
        props0->setProperty("Ice.Trace.ThreadPool", "1");

        /* create global ice communicator */
        Ice::InitializationData id;
        id.properties = props0;
        m_ich = Ice::CommunicatorHolder(id);
    }

    bool start(QObject *implement) {

        try {
            /* create client object and add it to ice adapter to receive server callbacks.
             * The adapter is created without identification as we donot access it by endpoints.
             * Instead, we pass it through the connection established with server to build a bidirectional connection.
             */
            m_ident = "Client";
            shared_ptr<ClientI> servant = make_shared<ClientI>();
            servant->setImplement(implement);
            m_adapter = m_ich->createObjectAdapter("");
            m_adapter->add(servant, Ice::stringToIdentity(m_ident));
            m_adapter->activate();
        } catch (const exception &e) {
            cout << "Failed to create ice object, error-->%s" << e.what() << endl;
            return false;
        }

        /* create ice service requirer in seperate thread, as network request may be time-consuming */
        m_requirer = new ServerRequirer(m_ich, m_adapter, m_ident);
        m_requirer->moveToThread(this);
        connect(this, SIGNAL(signal_requireService(string)), m_requirer, SLOT(slot_requireServcie(string)));

        QThread::start();
        return true;
    }

public slots:
    void slot_requireService() {
        string s("Hello world!");
        emit signal_requireService(s);
    }

signals:
    void signal_requireService(string s);

private:
    Ice::CommunicatorHolder m_ich;
    Ice::ObjectAdapterPtr   m_adapter;

    string          m_ident;        /* local object identification */
    ServerRequirer *m_requirer;
};

class MainWorker : public QObject
{
public:
    MainWorker(QObject *parent = nullptr) : QObject(parent) {}

protected:

    /* Receive callbacks from server and deliver to associated callback function */
    void customEvent(QEvent *e) {
        CustomEvent *event = (CustomEvent *)e;

        int type = event->type() - QEvent::User;
        if (CustomEvent::CustomEvent_RequireCallback == type) {
            renderCallback(event->m_params);
        } else {
            cout << "Unrecognized event type-->" << type << "!" << endl;
        }
    }

private:
    /* a simple implement */
    void renderCallback(const string& s) {
        cout << s << endl;
    }
};

#endif // HELPER_H

client main文件代码

#include "helper.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    /* local worker */
    MainWorker worker(&a);

    /* ice service manager */
    IceManager ice_manager;
    ice_manager.start(&worker);

    /* require serve service every 3 seconds */
    QTimer timer;
    QObject::connect(&timer, SIGNAL(timeout()), &ice_manager, SLOT(slot_requireService()));
    timer.start(3 * 1000);

    return a.exec();
}