text: // The MIT License (MIT)
  //
  // Copyright (c) Itay Grudev 2015 - 2018
  //
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  //
  // The above copyright notice and this permission notice shall be included in
  // all copies or substantial portions of the Software.
  //
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  // THE SOFTWARE.
  
  #include <QtCore/QTime>
  #include <QtCore/QThread>
  #include <QtCore/QDateTime>
  #include <QtCore/QByteArray>
  #include <QtCore/QSharedMemory>
  
  #include "singleapplication.h"
  #include "singleapplication_p.h"
  
  /**
   * @brief Constructor. Checks and fires up LocalServer or closes the program
   * if another instance already exists
   * @param argc
   * @param argv
   * @param {bool} allowSecondaryInstances
   */
  SingleApplication::SingleApplication(int &argc, char *argv[], const char* appName, bool allowSecondary, Options options, int timeout )
      : app_t( argc, argv ), d_ptr( new SingleApplicationPrivate( this ) )
  {
      Q_D(SingleApplication);
  
  #if defined(Q_OS_ANDROID) || defined(Q_OS_IOS)
      // On Android and iOS since the library is not supported fallback to
      // standard QApplication behaviour by simply returning at this point.
      qWarning() << "SingleApplication is not supported on Android and iOS systems.";
      return;
  #endif
  
      // Store the current mode of the program
      d->options = options;
  
      // Generating an application ID used for identifying the shared memory
      // block and QLocalServer
      d->genBlockServerName(appName);
  
  #ifdef Q_OS_UNIX
      // By explicitly attaching it and then deleting it we make sure that the
      // memory is deleted even after the process has crashed on Unix.
      d->memory = new QSharedMemory( d->blockServerName );
      d->memory->attach();
      delete d->memory;
  #endif
      // Guarantee thread safe behaviour with a shared memory block.
      d->memory = new QSharedMemory( d->blockServerName );
  
      // Create a shared memory block
      if( d->memory->create( sizeof( InstancesInfo ) ) ) {
          // Initialize the shared memory block
          d->memory->lock();
          d->initializeMemoryBlock();
          d->memory->unlock();
      } else {
          // Attempt to attach to the memory segment
          if( ! d->memory->attach() ) {
              qCritical() << "SingleApplication: Unable to attach to shared memory block.";
              qCritical() << d->memory->errorString();
              delete d;
              ::exit( EXIT_FAILURE );
          }
      }
  
      InstancesInfo* inst = static_cast<InstancesInfo*>( d->memory->data() );
      QTime time;
      time.start();
  
      // Make sure the shared memory block is initialised and in consistent state
      while( true ) {
          d->memory->lock();
  
          if( d->blockChecksum() == inst->checksum ) break;
  
          if( time.elapsed() > 5000 ) {
              qWarning() << "SingleApplication: Shared memory block has been in an inconsistent state from more than 5s. Assuming primary instance failure.";
              d->initializeMemoryBlock();
          }
  
          d->memory->unlock();
  
          // Random sleep here limits the probability of a collision between two racing apps
          qsrand( QDateTime::currentMSecsSinceEpoch() % std::numeric_limits<uint>::max() );
          QThread::sleep( 8 + static_cast <unsigned long>( static_cast <float>( qrand() ) / RAND_MAX * 10 ) );
      }
  
      if( inst->primary == false) {
          d->startPrimary();
          d->memory->unlock();
          return;
      }
  
      // Check if another instance can be started
      if( allowSecondary ) {
          inst->secondary += 1;
          inst->checksum = d->blockChecksum();
          d->instanceNumber = inst->secondary;
          d->startSecondary();
          if( d->options & Mode::SecondaryNotification ) {
              d->connectToPrimary( timeout, SingleApplicationPrivate::SecondaryInstance );
          }
          d->memory->unlock();
          return;
      }
  
      d->memory->unlock();
  
      d->connectToPrimary( timeout, SingleApplicationPrivate::NewInstance );
  
      delete d;
  
      ::exit( EXIT_SUCCESS );
  }
  
  /**
   * @brief Destructor
   */
  SingleApplication::~SingleApplication()
  {
      Q_D(SingleApplication);
      delete d;
  }
  
  bool SingleApplication::isPrimary()
  {
      Q_D(SingleApplication);
      return d->server != nullptr;
  }
  
  bool SingleApplication::isSecondary()
  {
      Q_D(SingleApplication);
      return d->server == nullptr;
  }
  
  quint32 SingleApplication::instanceId()
  {
      Q_D(SingleApplication);
      return d->instanceNumber;
  }
  
  qint64 SingleApplication::primaryPid()
  {
      Q_D(SingleApplication);
      return d->primaryPid();
  }
  
  bool SingleApplication::sendMessage( QByteArray message, int timeout )
  {
      Q_D(SingleApplication);
  
      // Nobody to connect to
      if( isPrimary() ) return false;
  
      // Make sure the socket is connected
      d->connectToPrimary( timeout,  SingleApplicationPrivate::Reconnect );
  
      d->socket->write( message );
      bool dataWritten = d->socket->waitForBytesWritten( timeout );
      d->socket->flush();
      return dataWritten;
  }
  