lambda.cpp

// core
#include <QObject>
#include <QTimer>
#include <QDebug>

// network
#include <QLocalSocket>
#include <QLocalServer>

// widgets
#include <QApplication>

// POSIX
#include <signal.h>
#include <unistd.h>

void catchUnixSignals(const std::vector<int>& quitSignals,
                      const std::vector<int>& ignoreSignals = std::vector<int>()) {

    auto handler = [](int sig) ->void {
        printf("\nquit the application (user request signal = %d).\n", sig);
        QCoreApplication::quit();
    };

    // all these signals will be ignored.
    for ( int sig : ignoreSignals )
        signal(sig, SIG_IGN);

    // each of these signals calls the handler (quits the QCoreApplication).
    for ( int sig : quitSignals )
        signal(sig, handler);
}

int main( int argc, char** argv )
{
    QApplication app( argc, argv );
    catchUnixSignals({ SIGQUIT, SIGINT, SIGTERM, SIGHUP });

        QLocalServer ipc;
        if ( ipc.listen( "/tmp/ipc" ) )
        {
            QObject::connect( &ipc, &QLocalServer::newConnection,
                [&]()
                {
                    auto socket = ipc.nextPendingConnection();

                    QObject::connect( socket, &QIODevice::readyRead,
                        [socket]()
                        {
                            QDataStream stream( socket );
                            QList<QString> args;
                            stream >> args;
                            qDebug() << args;
                        } );
                } );
        }
        else
        {
            if ( ipc.serverError() == QAbstractSocket::AddressInUseError )
            {
                QTimer::singleShot( 0,
                    [&]()
                    {
                        QLocalSocket* socket = new QLocalSocket( &app );
                        socket->connectToServer( "/tmp/ipc", QIODevice::WriteOnly );
                        if ( socket->waitForConnected( 1000 ) )
                        {
                            QDataStream input( socket );
                            QList<QString> args = QCoreApplication::arguments();
                            input << args;
                            socket->waitForBytesWritten( 30000 );
                            socket->flush();
                            QCoreApplication::quit();
                        }
                        else
                            QCoreApplication::exit( -1 );
                    } );
            }
        }

    return app.exec();
}