[Discuss-gnuradio] synchronization throughout flowgraph

[Vincenzo Pellegrini]

Hi everybody,
just a very simple question:
is there a clean way in GNURadio to do this

source-->block1-->block2

where:
source sends let's say some gr_complex 
block 1 looks for some synchro signal within the flow

block2 does absolutely nothing (i.e. does not process zeors or anything, simply it is frozen) untill block1 says: "well your frame starts here" and delivers a vector for block 2 to work upon.

It would be great if any body who's been doing this sort of things could provide some pointer to start from.

thank you all

vincenzo 

PS.
If this is not a sane way to arrange a flowgraph for doing syncronization, please point me to the sane way... ;-)
Maybe I should only use stream-oriented blocks that decide what to do and when, just based on some block internal state?