About flowgraph stop and blocks sending last-data-indicator

[Jonas Wenner]

Hello,
 
long time lurker, first time poster + newbie in GNURadio and digital signal 
processing here.
I'm terribly sorry if the question I'm about to ask is already answered in the 
wiki (couldn't find anything so far).
 
I have a question about flowgraph deconstruction / end of execution for message 
blocks.
 
Imagine, I have two message passing blocks (written in C++). One msg_send that 
periodically sends a message to a msg_recv block.
Now, for one reason or another, I'd like msg_recv to know that the message it 
receives is the last one msg_send will send due to someone/thing stopping the 
flowgraph.
Is it possible to propagate this somehow aka can msg_send be aware that the 
flowgraph should stop and send a special message to msg_recv?
I tried building this into msg_send's destructor and, while the message gets 
sent, it never arrives at msg_receive (I imagine due to a disconnect call on 
flowgraph end).
So for this to work, msg_send would need to know it is done with its entire 
work in its work function / message generation function (before the block gets 
disconnected). Is this possible in any way?
 
On that note, I have a few related questions I couldn't find the answer for:
- Is it guaranteed that a message will arrive at its destination as long as the 
flowgraph is connected, or can it be dropped somewhere between two blocks?
- What would be the order of block destruction when stopping a flowgraph? Is it 
first created - last destroyed?
 
Thanks in advance for your help and time
JW