After the network connection was disconnected, the CPU usage did not decrease

[jphz]

//
// EchoServer.cpp
//
// This sample demonstrates the SocketReactor and SocketAcceptor classes.
//
// Copyright (c) 2005-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//

#include <iostream>

#include "Poco/Delegate.h"
#include "Poco/Exception.h"
#include "Poco/FIFOBuffer.h"
#include "Poco/NObserver.h"
#include "Poco/Net/ServerSocket.h"
#include "Poco/Net/SocketAcceptor.h"
#include "Poco/Net/SocketNotification.h"
#include "Poco/Net/SocketReactor.h"
#include "Poco/Net/StreamSocket.h"
#include "Poco/Thread.h"
#include "Poco/Util/HelpFormatter.h"
#include "Poco/Util/Option.h"
#include "Poco/Util/OptionSet.h"
#include "Poco/Util/ServerApplication.h"

using Poco::AutoPtr;
using Poco::delegate;
using Poco::FIFOBuffer;
using Poco::NObserver;
using Poco::Thread;
using Poco::Net::ReadableNotification;
using Poco::Net::ServerSocket;
using Poco::Net::ShutdownNotification;
using Poco::Net::SocketAcceptor;
using Poco::Net::SocketReactor;
using Poco::Net::StreamSocket;
using Poco::Net::WritableNotification;
using Poco::Util::Application;
using Poco::Util::HelpFormatter;
using Poco::Util::Option;
using Poco::Util::OptionSet;
using Poco::Util::ServerApplication;

class EchoServiceHandler
/// I/O handler class. This class (un)registers handlers for I/O based on
/// data availability. To ensure non-blocking behavior and alleviate spurious
/// socket writability callback triggering when no data to be sent is available,
/// FIFO buffers are used. I/O FIFOBuffer sends notifications on transitions
/// from [1] non-readable (i.e. empty) to readable, [2] writable to non-writable
/// (i.e. full) and [3] non-writable (i.e. full) to writable.
/// Based on these notifications, the handler member functions react by
/// enabling/disabling respective reactor framework notifications.
{
public:
    EchoServiceHandler(StreamSocket& socket, SocketReactor& reactor)
        : _socket(socket)
        , _reactor(reactor)
        , _fifoIn(BUFFER_SIZE, true)
        , _fifoOut(BUFFER_SIZE, true) {
        Application& app = Application::instance();
        app.logger().information("Connection from " + socket.peerAddress().toString());

        _reactor.addEventHandler(
            _socket, NObserver<EchoServiceHandler, ReadableNotification>(*this, &EchoServiceHandler::onSocketReadable));
        _reactor.addEventHandler(
            _socket, NObserver<EchoServiceHandler, ShutdownNotification>(*this, &EchoServiceHandler::onSocketShutdown));

        _fifoOut.readable += delegate(this, &EchoServiceHandler::onFIFOOutReadable);
        _fifoIn.writable += delegate(this, &EchoServiceHandler::onFIFOInWritable);
    }

    ~EchoServiceHandler() {
        Application& app = Application::instance();
        try {
            app.logger().information("Disconnecting " + _socket.peerAddress().toString());
        } catch (...) {
        }
        _reactor.removeEventHandler(
            _socket, NObserver<EchoServiceHandler, ReadableNotification>(*this, &EchoServiceHandler::onSocketReadable));
        _reactor.removeEventHandler(
            _socket, NObserver<EchoServiceHandler, WritableNotification>(*this, &EchoServiceHandler::onSocketWritable));
        _reactor.removeEventHandler(
            _socket, NObserver<EchoServiceHandler, ShutdownNotification>(*this, &EchoServiceHandler::onSocketShutdown));

        _fifoOut.readable -= delegate(this, &EchoServiceHandler::onFIFOOutReadable);
        _fifoIn.writable -= delegate(this, &EchoServiceHandler::onFIFOInWritable);
    }

    void onFIFOOutReadable(bool& b) {
        if (b)
            _reactor.addEventHandler(_socket, NObserver<EchoServiceHandler, WritableNotification>(
                                                  *this, &EchoServiceHandler::onSocketWritable));
        else
            _reactor.removeEventHandler(_socket, NObserver<EchoServiceHandler, WritableNotification>(
                                                     *this, &EchoServiceHandler::onSocketWritable));
    }

    void onFIFOInWritable(bool& b) {
        if (b)
            _reactor.addEventHandler(_socket, NObserver<EchoServiceHandler, ReadableNotification>(
                                                  *this, &EchoServiceHandler::onSocketReadable));
        else
            _reactor.removeEventHandler(_socket, NObserver<EchoServiceHandler, ReadableNotification>(
                                                     *this, &EchoServiceHandler::onSocketReadable));
    }

    void onSocketReadable(const AutoPtr<ReadableNotification>& pNf) {
        try {
            int len = _socket.receiveBytes(_fifoIn);
            if (len > 0) {
                _fifoIn.drain(_fifoOut.write(_fifoIn.buffer(), _fifoIn.used()));
            } else {
                delete this;
            }
        } catch (Poco::Exception& exc) {
            Application& app = Application::instance();
            app.logger().log(exc);
            delete this;
        }
    }

    void onSocketWritable(const AutoPtr<WritableNotification>& pNf) {
        try {
            _socket.sendBytes(_fifoOut);
        } catch (Poco::Exception& exc) {
            Application& app = Application::instance();
            app.logger().log(exc);
            delete this;
        }
    }

    void onSocketShutdown(const AutoPtr<ShutdownNotification>& pNf) {
        delete this;
    }

private:
    enum { BUFFER_SIZE = 1024 };

    StreamSocket _socket;
    SocketReactor& _reactor;
    FIFOBuffer _fifoIn;
    FIFOBuffer _fifoOut;
};

class EchoServer
    : public Poco::Util::ServerApplication
/// The main application class.
///
/// This class handles command-line arguments and
/// configuration files.
/// Start the EchoServer executable with the help
/// option (/help on Windows, --help on Unix) for
/// the available command line options.
///
/// To use the sample configuration file (EchoServer.properties),
/// copy the file to the directory where the EchoServer executable
/// resides. If you start the debug version of the EchoServer
/// (EchoServerd[.exe]), you must also create a copy of the configuration
/// file named EchoServerd.properties. In the configuration file, you
/// can specify the port on which the server is listening (default
/// 9977) and the format of the date/time string sent back to the client.
///
/// To test the EchoServer you can use any telnet client (telnet localhost 9977).
{
public:
    EchoServer()
        : _helpRequested(false) {
    }

    ~EchoServer() {
    }

protected:
    void initialize(Application& self) {
        loadConfiguration();  // load default configuration files, if present
        ServerApplication::initialize(self);
    }

    void uninitialize() {
        ServerApplication::uninitialize();
    }

    void defineOptions(OptionSet& options) {
        ServerApplication::defineOptions(options);

        options.addOption(Option("help", "h", "display help information on command line arguments")
                              .required(false)
                              .repeatable(false));
    }

    void handleOption(const std::string& name, const std::string& value) {
        ServerApplication::handleOption(name, value);

        if (name == "help")
            _helpRequested = true;
    }

    void displayHelp() {
        HelpFormatter helpFormatter(options());
        helpFormatter.setCommand(commandName());
        helpFormatter.setUsage("OPTIONS");
        helpFormatter.setHeader("An echo server implemented using the Reactor and Acceptor patterns.");
        helpFormatter.format(std::cout);
    }

    int main(const std::vector<std::string>& args) {
        if (_helpRequested) {
            displayHelp();
        } else {
            // get parameters from configuration file
            unsigned short port = (unsigned short)config().getInt("EchoServer.port", 9977);

            // set-up a server socket
            ServerSocket svs(port);
            // set-up a SocketReactor...
            SocketReactor reactor;
            // ... and a SocketAcceptor
            SocketAcceptor<EchoServiceHandler> acceptor(svs, reactor);
            // run the reactor in its own thread so that we can wait for
            // a termination request
            Thread thread;
            thread.start(reactor);
            // wait for CTRL-C or kill
            waitForTerminationRequest();
            // Stop the SocketReactor
            reactor.stop();
            thread.join();
        }
        return Application::EXIT_OK;
    }

private:
    bool _helpRequested;
};

int main(int argc, char** argv) {
    EchoServer app;
    return app.run(argc, argv);
}