Tx/Rx stream stats related threads no longer have a direct reference to the
port's stream stats - instead they have their own copy that they keep and
return (in a reset-on-read fashion) when asked for. Each copy also has it's
own lock to prevent contention for read/update/clear.
PcapPort now fetches Tx(Transmitter) and Rx(Poller) stats on demand and
updates the port's stream stats - under protection of a lock.
The problem happens for bidirectional flows. The sequence of events is
as follows when you start Tx on Ports p1, p2 with the current code -
1. Clear stream stats on p1
2. Start tx on p1
3. Clear stream stats on p2
4. Start tx on p2
By the time #3 is executed, it may have already rx packets from p1 which
are being incorrectly cleared, this will cause these number of packets
to show up as dropped instead - incorrectly.
The fix is to change the order like this -
1. Clear stream stats on p1
2. Clear stream stats on p2
3. Start tx on p1
4. Start tx on p2
Unidirectional flows will not see this problem - as long as startTx is
done only on the Tx port and not the Rx port.
This bug is a regression caused due to the code changes introduced for the
stream stats rates feature implemented in 1.2.0
On some platforms and/or some libpcap verisons, libpcap doesn't support a
timeout which makes interactive stop not possible. So we now use a UNIX
signal to break out. Obviously this works only on *nix platforms - which
includes MacOS. For now the problem is not seen on Windows with WinPCAP,
so we should be fine. May need to revisit when we add Npcap support.
Fixes#215, #234
