how to test if a pipe contains data

[Christof Warlich]

Am 23.01.2012 09:43, schrieb Harald Becker:
> Hallo Laurent!
>
>>> Anyhow, if it helps, or even if someone is interested, I'm happy to
>>> explain in detail why I need to peek for data on a filedescriptor.
>>   I'd be interested in knowing why you need to do that. Maybe, by
>> looking at the big picture, we can help you design a solution that
>> fulfills your needs without this particular issue.
> You hit it exactly. Beside this I'm willing to help finding a solution
> and to do not only complain ... but it's absolute necessary to have the
> full picture to say anything about this.
>
> --
> Harald

I need to transfer data coming from a pipe over a UMTS link to a web server.
 From time to time, the UMTS link goes down, and worse, it sometimes cannot
be reestablished. I believe that in these cases, the firmware of the 
UMTS stick
hangs, but this is just a guess. Anyhow, the only way I could get the 
link up and
running again when this happens is to reboot the whole system.

As my application will have tried for quite a while to get the link up  
before
such drastic measures, quite some data may have accumulated in the pipe.
To avoid loosing that data, I need to drain the pipe to store its data 
to a file
surviving the recovery. This is the place where I just want to check if 
there
is still data in the pipe. If it is empty, I reboot.