On Fri, Jun 29, 2018 at 7:35 PM Kevin Reid <kpr...@switchb.org> wrote:
> On Fri, Jun 29, 2018 at 6:28 PM Martin Braun <martin.br...@ettus.com>
> wrote:
>
>> I'd like to discuss the removal of the old msg_queue API from GNU Radio. …
>>
> I will experiment and see if [Python blocks are] stable when used as a
> queue replacement.
>
I have now finished implementing the changeover but have not tested it much
yet. So far things seem OK, but I did find one gotcha.
The obvious straightforward thing to do if you are going to export data to
Python (that wants to not be running in the Python block's thread) is to do
something like the following. ('reactor' is from Twisted, an event loop
framework I am using.)
def work(self, input_items, output_items):
items_numpy_array = input_items[0]
self.reactor.callFromThread(self.callback, items_numpy_array)
return len(items_numpy_array)
However, this eventually segfaults.
In hindsight, it's obvious that the array ought to be copied, but I didn't
think of it the time and I imagine that most beginners trying to do this
wouldn't either, and it wasn't in the documentation for Python blocks (which
is sketchy, hard to find all of, and lacking in reference-not-tutorial
text).
Furthermore, as Python is a memory-safe language, making this mistake ought
to produce some kind of appropriate exception rather than an object which
could be used to corrupt memory. Such an exception would also be able to
help users learn how to fix the problem (if nothing else by giving it a
name other than "Segmentation fault").
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