I wrote the simple Tcp client-server app.
I have a Packet class, look like:
First 4 byte are the data type, and other are Data (QString) as Bytearray.

I have 3 threads.
Server -> User Manager -> Socket Thread.
So, when i try this ( for test ) :

Qt Code: 
  1. for(int i =  0; i < 5;i++){
  2.          Packet * teszt1 = new Packet;
  3.         teszt1->setType(12);
  4.         teszt1->setData("Something data teszt1 packet")
  5.  
  6.         Packet * teszt2 = new Packet;
  7.         teszt2->setType(21);
  8.         teszt2->setData("Something data teszt2 packet")
  9.  
  10. QMetaObject::invokeMethod(usersocket,"writeData",Qt::QueuedConnection,Q_ARG(Packet*,teszt1));
  11.  
  12. QMetaObject::invokeMethod(usersocket,"writeData",Qt::QueuedConnection,Q_ARG(Packet*,teszt2));
  13. }
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The package arrive ,but the teszt2 packet's type equal to the teszt1. (The data is different.)

BUT!!! When i add new line to my writeData method: QThread::msleep(30); It's work!
Why???

My writeData method:

Qt Code: 
  1. void socketThread::writeData(Packet * packet)
  2. {
  3.     if(Socket->state() == QAbstractSocket::ConnectedState)
  4.     {
  5.         qDebug() << "Type: " << packet->getType(); //
  6.         qDebug() << "Data: " << packet->getStringData(); 
  7.         QByteArray kuldendo;
  8.         *packet >> kuldendo;
  9.         QByteArray Packetsize= Packet::IntToArray(packet->sizeOfPacket());
  10.         Socket->write(Packetsize); //Sizeof(Packet type + Packet data)
  11.         Socket->write(kuldendo); //Packet type + Packet data
  12.         Socket->waitForBytesWritten();
  13.         QThread::msleep(30); // <- without not work.
  14.     }
  15.     delete packet;
  16. }
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The client-side output without QThread::msleep(30) show :

Qt Code: 
  1. ---------------------
  2. Packet Type: 12
  3. Packet Data: "Something data teszt1 packet"
  4. ---------------------
  5. NEW MESSAGE FROM SERVER
  6. ---------------------
  7. Packet Type: 12
  8. Packet Data: "Something data teszt2 packet"
  9. ---------------------
  10. NEW MESSAGE FROM SERVER
  11. ---------------------
  12. Packet Type: 12
  13. Packet Data: "Something data teszt1 packet"
  14. ---------------------
  15. NEW MESSAGE FROM SERVER
  16. ---------------------
  17. Packet Type: 12
  18. Packet Data: "Something data teszt2 packet"
  19. ---------------------
  20. NEW MESSAGE FROM SERVER
  21. ---------------------
  22. Packet Type: 12
  23. Packet Data: "Something data teszt1 packet"
  24. ---------------------
  25. NEW MESSAGE FROM SERVER
  26. ---------------------
  27. Packet Type: 12
  28. Packet Data: "Something data teszt2 packet"
  29. ---------------------
  30. NEW MESSAGE FROM SERVER
  31. ---------------------
  32. Packet Type: 12
  33. Packet Data: "Something data teszt1 packet"
  34. ---------------------
  35. NEW MESSAGE FROM SERVER
  36. ---------------------
  37. Packet Type: 12
  38. Packet Data: "Something data teszt2 packet"
  39. ---------------------
  40. NEW MESSAGE FROM SERVER
  41. ---------------------
  42. Packet Type: 12
  43. Packet Data: "Something data teszt1 packet"
  44. ---------------------
  45. NEW MESSAGE FROM SERVER
  46. ---------------------
  47. Packet Type: 12
  48. Packet Data: "Something data teszt2 packet"
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I use Qt 5.7 with Static mingw compiler.
(OS: Windows 10)