Async message flow control

How does one achieve flow control with the new style message passing
API? I have a use case in which I’m generating packets in one flowgraph
and pushing them through a pdu_to_tagged_stream (P2TS) block to be
modulated in another flowgraph. I believe I’m overwhelming the P2TS
block’s queue because I get warnings about dropped messages. One hack I
made was to insert a throttle block into the packet generating
flowgraph. This helped a bit, but I have to guess the magic throttle
rate at which I don’t fill up the queue. Is there a way to have P2TS
block when its queue is full and therefore generate backpressure on the
upstream flowgraph?

I basically have flowgraph (FG1) --> message domain --> flowgraph (FG2)
–> USRP. FG1’s flow rate is not constrained by streaming backpressure.
FG2’s flow rate is constrained by a USRP. To constrain FG1’s flow rate I
either have to use a throttle block or find a way to enforce flow
control in the message domain.


On Wed, Feb 26, 2014 at 12:00 PM, Nowlan, Sean
[email protected] wrote:


Nope, no flow control on the message ports. Their original design was
for control and meta data messages, but we quickly realized their
capabilities with passing packets. Flow control here is one of our
identified problems that we don’t have a current solution for. In
other words, if you come up with something, we’d be very interested to
hear it and will definitely work with you on it.