[Discuss-gnuradio] How to control the open and close state of a flow graph

[Zhonghua]

Hi every one,

I am trying to control the open and close state of the flow graph which 
implements transmission and receiving tasks. I would not like to use 
start() and stop() pair to do that because the construction time is too 
long. What I expect is sending a signal from another process to control 
the flow graph of local process.
The architecture is very simple. In RX channel, Using uhd.usrp_source() 
to get flow and transferring it to a signal process block for example 
ieee802_15_4_demod_pkts().  TX part transferring flow from 
ieee802_15_4_mod_pkts to uhd.usrp_sink(). The RX and TX are put in two 
separate top_block and control them respectively. The simplest method I 
used to control is lock() and unlock(). My scenario is that when signal 
A arrived , call lock(), then when signal B arrived call unlock() to 
revive the flow. The result is sometimes in the period of signal A the 
flow does not stop and there is still data transferred from usrp_source 
to demod_pks block. Then, I try to use method that combines lock() + 
disconnect()+unlock() to stop the flow. For reviving the flow, 
lock()+connect()+unlock() is used. The result is identical with the 
former experiment.
At last I realised maybe the usrp_source is two slow so it block the 
signal handler's action. To verify it, I added the period of signal B to 
give adequate time for the data transferring from usrp_source to the 
demod_pkts(). I found the signal handler's action became almost regular. 
If I came back to the old time configuration but set a lower sample rate 
of the uhd.usrp_source(), the signal handler's action also became regular.
So now my question is if I have to keep a small period of signal B and 
simultaneously a relatively high sample rate, how can I control the 
flow? Are there some approaches to mute the usrp_source thoroughly at 
the period of signal B?
Any suggestion is highly appreciated.

Sincerely,

Zhonghua