Hi,

Using Qt 5.14.1.

If I write back to back on a QUdpSocket, the subsequent datagrams never make it out. For example:
Qt Code: 
  1. #include <QCoreApplication>
  2. #include <QUdpSocket>
  3. #include <QTextStream>
  4. #include <QThread>
  5.  
  6. int main(int argc, char *argv[])
  7. {
  8. 	QTextStream	cout(stdout);
  9. 	QUdpSocket	myUdpSocket;
  10.  
  11. 	myUdpSocket.connectToHost("127.0.0.1", 50000);
  12.  
  13. 	cout << myUdpSocket.write("msg 1\n") << Qt::endl;
  14. 	cout << myUdpSocket.write("msg two\n") << Qt::endl;
  15.  
  16. 	QThread::currentThread()->sleep(5);
  17.  
  18. 	return 0;
  19. }
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Both writes return that they wrote the expected number of bytes (6 and 8).

Per Wireshark, only the first write (i.e., "msg 1\n") is actually sent out.

"1","0.000000","127.0.0.1","127.0.0.1","UDP","58", "54399 ? 50000 Len=6","msg 1\n"

If I put in a delay, then it works:
Qt Code: 
  1. cout << myUdpSocket.write("msg 1\n") << Qt::endl;
  2.  
  3. QThread::currentThread()->sleep(1);
  4.  
  5. cout << myUdpSocket.write("msg two\n") << Qt::endl;
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Wireshark output:

"1","0.000000","127.0.0.1","127.0.0.1","UDP","58", "53420 ? 50000 Len=6","msg 1\n"
"2","1.000014","127.0.0.1","127.0.0.1","UDP","68", "53420 ? 50000 Len=8","msg two\n"

I also tried waitForBytesWritten(), and that didn't work (the calls to it each return false):
Qt Code: 
  1. cout << myUdpSocket.write("msg 1\n") << Qt::endl;
  2.  
  3. cout << myUdpSocket.waitForBytesWritten(1000) << Qt::endl;
  4.  
  5. cout << myUdpSocket.write("msg two\n") << Qt::endl;
  6.  
  7. cout << myUdpSocket.waitForBytesWritten(1000) << Qt::endl;
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I am fairly new to Qt so my apologies if I am missing something seemingly obvious. Any help understanding why QUdpSocket and/or write() is behaving this way is greatly appreciated. Thank you.