Nicholas,
Please excuse me but I must ask you how exactly you use select(). I've
seen many people use select() the wrong way. It would be a shame if you
did not follow through with this before abandoning it.
It should work - what do you mean "when trying to transmit, select()
terminates with a timeout"?
Do you call send() and then select() on the socket or the other way
around? do you clear all sets before each call to select()?
p.s I am not sure this discussion is within the board's scope anymore.
We may want to take this offline.
On 11/01/10 16:24 PM, Nicolas Pinault wrote:
Yoav Nissim a écrit :
Simon,
Is the half duplex limitation only a socket implementation issue? other
than the missing locks, what else is missing? using the netconn API
seems to result in the same problem.
Isn't the TCPIP thread performing operations one at a time anyway?
Nicolas,
I'm sorry. I tried thinking about this for a while but the only way I
could produce any helpful code here is if I throw myself into actually
coding and testing it... my boss would not like that I imagine :)
Ok. I understand. No problem.
Are you working with existing vnc server code
that uses two threads, or are you writing the code yourself?
My code is based on a code I have found in eCos svn tree. The original
code uses 2 threads. One for receiving commands from client and one for
sending screen content.
If you have existing code, maybe you should
try serializing the send and receive operations with a separate thread
using select as I've suggested earlier.
I have modified my code to use only one thread. The result is
catastrophic. It works worse than ever. When trying to transmit,
select() terminates with a timeout (1sec)
If you are writing your own code, could you
clarify why a single thread (not the main) using select and doing all
Rx and Tx would not work?
select() blocks until data are received or timeout occurs.
The system screen is updated by another thread. When the screen has
been updated, screen content must be sent to the client.
How do you go out of select() if you don't use timeout ?
Nicolas
Yoav.
On 11/01/10 11:33 AM, Nicolas Pinault wrote:
Simon,
Simon Goldschmidt a écrit :
2. Keep Rx and Tx threads locked and
waiting on a select running in
another thread (in essence adding the locking mechanism that lwIP does
not support)
The idea is good, but it's not what lwIP doesn't support, since you
don't get full duplex but mutual exclusion for read & write. Full
duplex would allow simultaneously sending and receiving on the wire.
However, that's the best you can get, currently, when using sockets.
My problem is not to simultaneously receive and transmit data.
My problem is that I have an application that receives data and
transmit data asynchronously.
My application is a vnc server.
Vnc server receives data from client when, for example, the user moves
the mouse or hits keys.
Vnc server sends screen content to client when needed.
The client can request the server to force send screen content. In this
case, no problem.
But vnc server can also need to send screen content while nothing is
received.
Two threads are ideal in this situation. One for receiving commands and
one for sending screen content.
I can't see any other solution than using select with a short timeout.
Nicolas
Simon
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Fax: +972-74-7212122
Mobile: +972-54-2271315
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