[collectd] issue on shutdown with 4.10

[Marc Fournier]

Hello,

On systems running 4.10.0 or 37e18082, I discovered that the socket created
by the unixsocket plugin was sometimes not removed on shutdown, which
prevents the plugin from working with this error at the next restart:

  unixsock plugin: bind failed: Address already in use

This problem is non-systematic. I tried to strace collectd, but didn't find
any obvious error. But I did notice that when the socket fails to get
removed, strace exits with an error:

$ strace -f -s0 -o /tmp/strace.txt -p 30699
Process 30699 attached with 10 threads - interrupt to quit
Process 30708 detached
Process 30709 detached
Process 30707 detached
Process 30705 detached
Process 30704 detached
PANIC: handle_group_exit: 30703 leader 30699
PANIC: handle_group_exit: 30702 leader 30699
PANIC: handle_group_exit: 30701 leader 30699
PANIC: handle_group_exit: 30700 leader 30699

When the socket gets removed, strace ends without "panicking".

NB: I checked file and dir modes, collectd can create/remove the socket
file without restriction.

Any suggestions how I could dig further in order to find out what's going
on ?

Thanks !
Marc