This allows the queue to be used in a single process for multiple possibly
conflicting commands, like add and rm, without running them out of order.
This assumes that running the same git subcommand with different parameters
cannot itself conflict.
When a new file is annexed, a deletion event occurs when it's moved away
to be replaced by a symlink. Most of the time, there is no problimatic
race, because the same thread runs the add event as the deletion event.
So, once the symlink is in place, the deletion code won't run at all,
due to existing checks that a deleted file is really gone.
But there is a race at startup, as then the inotify thread is running
at the same time as the main thread, which does the initial tree walking
and annexing. It would be possible for the deletion inotify to run
in a perfect race with the addition, and remove the newly added symlink
from the git cache.
To solve this race, added event serialization via a MVar. We putMVar
before running each event, which blocks if an event is already running.
And when an event finishes (or crashes!), we takeMVar to free the lock.
Also, make rm -rf not spew warnings by passing --ignore-unmatch when
deleting directories.
And just like that, annexed files can be moved and copies around within
the tree, and are automatically fixed to point to the content, and staged
in git. Huzzah!
Delete still remains TODO, with its troublesome race during add..
This fixes the scenario where:
* directory foo is moved away (and still watched)
* a new directory foo is made
* file (or directory) foo/bar is created
* the old directory's file (or directory) "bar" is deleted
We don't want a deletion event for foo/bar in this case.
There are two reasons for this test. First, there could be a fifo or other
non-regular file that was closed.
Second, this test avoids ugliness when a subdirectory is moved out of the
top of the watch directory to elsewhere, and a file added to it.
Since the subdirectory has moved, the file won't be present under the
old location, and nothing will be done.
I cannot find a way to stop watching such directories, at least not without
a lot of pain. The inotify interface in Haskell doesn't make it easy to
stop watching a given subdirectory when it's moved out; it would require
keeping a map of all watch handles that is shared between threads.
This workaround avoids the problem in most cases; the only remaining case
being deletion of a file from a moved subdirectory.
Improved the inotify code, so it will also notice directory removal
and symlink creation.
In the watch code, optimised away a stat of a file that's being added,
that's done by Command.Add.start. This is the reason symlink creation is
handled separately from file creation, since during initial tree walk
at startup, a stat was already done, and can be reused.
