Incoming data loss due to TCPStream::sync(void) gettting called if the a tcpstream is flushed!

[Georg Soffel]

Hello all,

I am using the tcpstream class in binary mode:

    mystream.setf(ios::binary);
    mystream.unsetf(ios::skipws);

I wrote stream operators for a message class
which are used to send and receive messages via the stream socket, like :

  mystream >> msg;

for receiving a message from the stream and:

  mystream << msg << flush;

for sending a message to the stream.

Now I noticed an incoming message loss. Further investigations showed that
the reason was due to the fact that the call to flush led to a call of the
sync function
in the TCPStream class. This was not what I expected! I wanted only to get
the
message send immediately by the flush and not clear my incoming buffer.
I am not an expert with steam and stream buffer classes in the Standard C++
Library but I think this is not the desired behaviour.

I solved the problem by writing my own "Flush" function:

class mytcpstream : public tcpstream {
public:
    void Flush(void) {   // flush without clearing the incoming buffer
            overflow(EOF);
    }
    Error setNoDelay(bool enable) {   // disable nagle for better
performance
            return Socket::setNoDelay(enable);
    }
};

Now

  mystream << msg; mystream.Flush();

works fine without any message loss even under high load.


Please give me some feedback/comments. This problem probably also
occurs if the stream is not used in binary mode and "endl" is used!

Regards
Georg Soffel

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