yarpserver crashes using persistent connections

[claudiofantacci]

Following issue #1437 and PR #1460, I would like to report the following issue involving persistent connections and yarpserver.

I used to use persistent connection in one of my YARP module in order to avoid reconnecting ports every time the module was rerun.
I noticed that after several runs, between 8 and 10, of my module yarpserver was crashing.
By removing persistent connection crashes disappeared.

Please consider the following:

• this issue happened quite some months ago, an I lost track of it, my bad 😔
• I don't recall which was exactly the error upon yarpserver crash, it may was a segmentation fault
• the issue was quite repeatable and I am sure that the application was always closing correctly

[claudiofantacci]

cc @traversaro @barbalberto @drdanz @lornat75

[barbalberto]

Thanks for reporting, if you remember more details and/or have time to write a test case that'll be awesome!

[claudiofantacci]

@barbalberto it should not be difficult, the application should be like this:

1. Module A opens some connections
2. Module B opens some connections
3. Connect them with persistent option
4. Send some data
5. Close the applications smoothly
6. Repeat from 1. several times
   which is a reasonable approximation of what was done in my module.

Having said that, I can write a test bench as soon as I have some time 👍