Junio C Hamano <gits...@pobox.com> writes:
> I checked read-cache.c and preload-index.c code. To get the
> discussion rolling, I think something like the outline below may be
> a good starting point and a feasible weekend hack for somebody
> * At the beginning of preload_index(), instead of spawning the
> worker thread and doing the lstat() check ourselves, we open a
> socket to our daemon (see below) that watches this repository and
> make a request for lstat update. The request will contain:
> - The SHA1 checksum of the index file we just read (to ensure
> that we and our daemon share the same baseline to
> communicate); and
> - the pathspec data.
> Our daemon, if it already has a fresh data available, will give
> us a list of <path, lstat result>. Our main process runs a loop
> that is equivalent to what preload_thread() runs but uses the
> lstat() data we obtained from the daemon. If our daemon says it
> does not have a fresh data (or somehow our daemon is dead), we do
> the work ourselves.
> * Our daemon watches the index file and the working tree, and
> waits for the above consumer. First it reads the index (and
> remembers what it read), and whenever an inotify event comes,
> does the lstat() and remembers the result. It never writes
> to the index, and does not hold the index lock. Whenever the
> index file changes, it needs to reload the index, and discard
> lstat() data it already has for paths that are lost from the
> updated index.
I left the details unsaid in thee above because I thought it was
fairly obvious from the nature of the "outline", but let me spend a
few more lines to avoid confusion.
- The way the daemon "watches" the changes to the working tree and
the index may well be very platform dependent. I said "inotify"
above, but the mechanism does not have to be inotify.
- The channel the daemon and the client communicates would also be
system dependent. UNIX domain socket in $GIT_DIR/ with a
well-known name would be one possibility but it does not have to
be the only option.
- The data given from the daemon to the client does not have to
include full lstat() information. They start from the same index
info, and the only thing preload_index() wants to know is for
which paths it should call ce_mark_uptodate(ce), so the answer
given by our daemon can be a list of paths.
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