Hi Thu,

On Thu, Aug 26, 2010 at 11:13 AM, Vo Minh Thu <noteed@gmail.com> wrote:

Is is possible to get Network.Socket.ByteString.recv to be
non-blocking (i.e. return directly even if no data is available) ?

Unfortunately not.

I have tried ti use

setSocketOption sock NoDelay 1

but then I get the following error:

setSocketOption: unsupported operation (Protocol not available)

Sockets are already set to be non-blocking and the blocking semantics are implemented on top of non-blocking sockets using e.g. the select system call. It's not the recv syscall that blocks but the I/O manager who blocks you're thread because recv returned WOULD_BLOCK. The I/O manager calls threadWaitRead upon receiving this error. threadWaitRead puts the thread to sleep until the socket is readable (as indicated by select).

We could perhaps implement a truly non-blocking API.

Cheers,
Johan