[Haskell-cafe] non-blocking recv from UDP socket

Johan Tibell johan.tibell at gmail.com
Thu Aug 26 07:01:08 EDT 2010

Hi Thu,

On Thu, Aug 26, 2010 at 11:13 AM, Vo Minh Thu <noteed at 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.

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