UDP sockets and select()

I wrote a program that created a UDP socket (SOCKET_DGRAM) with the
expectation of reading UDP datagrams from it but select() claims that the
socket was never ready for reading.  Now, I _know_ there was data to be read
because replacing the select() call with a synchronous recvfrom() call
returns data!

So, what's up?  Why doesn't select() work connectionless sockets?  Is
this the same on all UNIX systems?  I'm trying this on Linux 2.4.21.
Thanks...

"Just Another Victim of the Ambient Morality" <ihatespam@rogers.com> writes:

>     I wrote a program that created a UDP socket (SOCKET_DGRAM) with the
> expectation of reading UDP datagrams from it but select() claims that the
> socket was never ready for reading.  Now, I _know_ there was data to be re
ad
> because replacing the select() call with a synchronous recvfrom() call
> returns data!
>
>     So, what's up?  Why doesn't select() work connectionless sockets?  Is
> this the same on all UNIX systems?  I'm trying this on Linux 2.4.21.

It has always worked for me on all Unixes I've tried.  Post some code
demonstrating the problem.

--
Måns Rullgård
mru@mru.ath.cx

"Just Another Victim of the Ambient Morality" <ihatespam@rogers.com> wrote in message news:
<zKS1d.257$RTE1.109@news01.bloor.is.net.cable.rogers.com>...
> I wrote a program that created a UDP socket (SOCKET_DGRAM) with the
> expectation of reading UDP datagrams from it but select() claims that the
> socket was never ready for reading.  Now, I _know_ there was data to be re
ad
> because replacing the select() call with a synchronous recvfrom() call
> returns data!
>
>     So, what's up?  Why doesn't select() work connectionless sockets?  Is
> this the same on all UNIX systems?  I'm trying this on Linux 2.4.21.
>     Thanks...

The select() system call works just fine with UDP on linux.  Trust me,
its not the kernel.  Its your code.

The number one select() mistake that everyone makes at one time or
another is incorrectly setting the first agument - the maximum fd
*plus one*.  Check that first.

dv

dv is right.

I've also posted a message to talk about this, and I realized that in
my implementation, I did put *1* in the first arguement on the
select(). If you can take a look at the man page, you will figure out
more. =)

- tikviva

dirtyvicar@hotmail.com (Dirty Vicar) wrote in message news:<b90dfd06.0409160810.4f56546e@po
sting.google.com>...
> "Just Another Victim of the Ambient Morality" <ihatespam@rogers.com> wrote
 in message news:<zKS1d.257$RTE1.109@news01.bloor.is.net.cable.rogers.com>..
. 
>
> The select() system call works just fine with UDP on linux.  Trust me,
> its not the kernel.  Its your code.
>
> The number one select() mistake that everyone makes at one time or
> another is incorrectly setting the first agument - the maximum fd
> *plus one*.  Check that first.
>
> dv

"Dirty Vicar" <dirtyvicar@hotmail.com> wrote in message
news:b90dfd06.0409160810.4f56546e@posting.google.com...
> "Just Another Victim of the Ambient Morality" <ihatespam@rogers.com> wrote
in message news:<zKS1d.257$RTE1.109@news01.bloor.is.net.cable.rogers.com>...
 
the 
read 
Is 
>
> The select() system call works just fine with UDP on linux.  Trust me,
> its not the kernel.  Its your code.
>
> The number one select() mistake that everyone makes at one time or
> another is incorrectly setting the first agument - the maximum fd
> *plus one*.  Check that first.

Ah, it turns out that that was, indeed, my problem.  Thanks for the
help!

I've got another question but I'll ask that in its own thread...