Re: UDP recvmsg blocks after select(), 2.6 bug?

Richard B. Johnson
2004-10-06T15:10:27Z

On Wed, 6 Oct 2004, Joris van Rantwijk wrote:

> Hello,
>
> I have a problem where the sequence of events is as follows:
> - application does select() on a UDP socket descriptor
> - select returns success with descriptor ready for reading
> - application does recvfrom() on this descriptor and this recvfrom()
> blocks forever
>
> My understanding of POSIX is limited, but it seems to me that a read call
> must never block after select just said that it's ok to read from the
> descriptor. So any such behaviour would be a kernel bug.
>

Can you check to see if you have an exception at the same time?
Also, please make sure that the first parameter to select() is
the file-descriptor value + 1. There are things like out-of-band
data that could show up ( MSG_OOB ) under select(). Also, recvfom()
takes a lot of parameters that need to be correct. There is a buffer
length plus a pointer to a socklen_t variable. I've seen people
mess these up and have everything "work" except sometimes...

Cheers,
Dick Johnson
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