The reason the DirWatcher had to wait for program termination was because
it used withINotify, so when it finished, its watcher threads were killed.
But since I have two DirWatcher threads now, that was not good, and could
perhaps explain the MVar problem I saw yesterday. In any case, fixed this
part of the code by making the DirWatcher return a handle that can be used
to stop it, and now the main Assistant thread is the only one calling
waitForTermination.
SampleMVar won't work; between getting the current value and changing
it, another thread could made a change, which would get lost.
TMVar works well; this update situation is handled by atomic transactions.
Rethought how to keep track of pending adds that need to be retried later.
The commit thread already run up every second when there are changes,
so let's keep pending adds queued as changes until they're safe to add.
Also, the committer is now smarter about avoiding empty commits when
all the adds are currently unsafe, or in the rare case that an add event
for a symlink is not received in time. It may avoid them entirely.
This seems to work as before for inotify, and is untested for kqueue.
(Actually commit batching seems to be improved for inotify, although I'm
not sure why. I'm seeing only two commits made during large batch
operations, and the first of those is the non-batch mode commit.)
Kqueue needs to remember which files failed to be added due to being open,
and retry them. This commit gets the data in place for such a retry thread.
Broke KeySource out into its own file, and added Eq and Ord instances
so it can be stored in a Set.
