Re: [Discuss-gnuradio] gr.head, and flushing of file sinks

[Eric Blossom]

On Tue, Oct 23, 2007 at 12:22:31PM -0400, Steven Clark wrote:
> 1) Has anybody ever noticed a case where gr.head doesn't seem to limit the
> amount of data that flows through it? I have (some data source) -> (head) ->
> (file sink), and sometimes the writing to the file shuts off appropriately,
> other times it seems to skip over the limit and would happily consume my
> entire hard drive (I watch the file grow to 50MB, 100MB, ...) if I didn't
> Ctrl-C. I'm having trouble reproducing this now, but thought I would ask.
> 
> 
> 2)
> b = MyTopBlockWhichWritesToAFileSink()
> b.start()
> b.wait()
> raw_input() #wait indefinitely for user to hit enter
> del b
> 
> b.wait() doesn't seem to do a final flush of the file sink...ie if b is
> supposed to write 10000 bytes to a file, after b.wait() the file will have
> 8.0KB (~8192 bytes) in it. Not until del b is the file complete (9.8KB,
> ~10000 bytes). What exactly does b.wait() do? Is there any way to force a
> file flush without deleting b?

You could call my_file_sink_instance.close(), which will flush and
close the underlying file.  This may not be exactly what you want.

> 
> 3) Is there anything wrong with having multiple sequential top blocks?
> Something like:
> 
> a = MyTopBlock1()
> a.start()
> a.wait()
> del a
> 
> for i in range(10):
>     b = MyTopBlock2()
>     b.start()
>     b.wait()
>     del b


It should work.  Doesn't mean that there isn't a bug somewhere,
particularly if you are using the pkt based stuff.  There was a report
of a hang related to something (the queue reader I think) hanging on a
message queue that was never seeing any further messages.

FWIW, the existing QA code uses serial top blocks without a problem.

If you're using the gr.udp_source, it's broken, and will result in
gr.head() never stopping.  It'll just hang.

In the random suggestion category: stylistically, instead of
b.start(), b.wait(), you may want to consider b.run().  It does the
start(), wait() for you.

If this didn't help, can you cook a simple example that has the
problem.  E.g., gr.file_source() -> gr.head() -> gr.file_sink()

Eric