Fix bug caused by recent optimisations that could make git-annex not see
recently recorded status information when configured with
annex.alwayscommit=false.
This does mean that --all can end up processing the same key more than once,
but before the optimisations that introduced this bug, it used to also behave
that way. So I didn't try to fix that; it's an edge case and anyway git-annex
behaves well when run on the same key repeatedly.
I am not too happy with the use of a MVar to buffer the list of files in the
journal. I guess it doesn't defeat lazy streaming of the list, if that
list is actually generated lazily, and anyway the size of the journal is
normally capped and small, so if configs are changed to make it huge and
this code path fire, git-annex using enough memory to buffer it all is not a
large problem.
Fix bug caused by recent optimisations that could make git-annex not see
recently recorded status information when configured with
annex.alwayscommit=false.
When not using --all, precaching only gets triggered when the
command actually needs location logs, and so there's no speed hit there.
This is a minor speed hit for --all, because it precaches even when the
location log is not actually going to be used, and so checking the journal
is not necessary. It would have been possible to defer checking the journal
until the cache gets used. But that would complicate the usual Branch.get
code path with two different kinds of caches, and the speed hit is really
minimal. A better way to speed up --all, later, would be to avoid
precaching at all when the location log is not going to be used.
