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

[Richard B. Johnson]

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
Penguin : Linux version 2.6.5-1.358-noreg on an i686 machine (5537.79 BogoMips).
            Note 96.31% of all statistics are fiction.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/