On 14/10/19 12:18AM, Johannes Schindelin wrote:
> Hi Pratyush,
>
> On Mon, 14 Oct 2019, Pratyush Yadav wrote:
>
> > On 12/10/19 11:24PM, Johannes Schindelin wrote:
> > > Hi Pratyush,
> > >
> > > On Sat, 12 Oct 2019, Pratyush Yadav wrote:
> > >
> > > > On 08/10/19 04:33AM, Johannes Schindelin via GitGitGadget wrote:
> > > >
> > > > > @@ -1453,10 +1501,16 @@ proc rescan {after {honor_trustmtime 1}} {
> > > > > global HEAD PARENT MERGE_HEAD commit_type
> > > > > global ui_index ui_workdir ui_comm
> > > > > global rescan_active file_states
> > > > > - global repo_config
> > > > > + global repo_config _gitdir_cache
> > > > >
> > > > > if {$rescan_active > 0 || ![lock_index read]} return
> > > > >
> > > > > + # Only re-prime gitdir cache on a full rescan
> > > > > + if {$after ne "ui_ready"} {
> > > >
> > > > What do you mean by a "full rescan"? I assume you use it as the
> > > > differentiator between `ui_do_rescan` (called when you hit F5 or choose
> > > > rescan from the menu) and `do_rescan` (called when you revert a line or
> > > > hunk), and a "full rescan" refers to `ui_do_rescan`.
> > > >
> > > > Well in that case, this check is incorrect. `do_rescan` passes only
> > > > "ui_ready" and `ui_do_rescan` passes "force_first_diff ui_ready".
> > > >
> > > > But either way, I'm not a big fan of this. This check makes assumptions
> > > > about the behaviour of its callers based on what they pass to $after.
> > > > The way I see it, $after should be a black box to `rescan`, and it
> > > > should make absolutely no assumptions about it.
> > > >
> > > > Doing it this way is really brittle, and would break as soon as someone
> > > > changes the behaviour of `ui_do_rescan`. If someone in the future passes
> > > > a different value in $after, this would stop working as intended and
> > > > would not refresh the cached list on a rescan.
> > > >
> > > > So, I think a better place for this if statement would be in
> > > > `ui_do_rescan`. This would mean adding a new function that does this.
> > > > But if we unset _gitdir_cache in prime_gitdir_cache (I see no reason not
> > > > to), we can get away with just something like:
> > > >
> > > > proc ui_do_rescan {} {
> > > > rescan {prime_gitdir_cache; ui_ready}
> > > > }
> > > >
> > > > Though since `prime_gitdir_cache` does not really depend on the rescan
> > > > being finished, something like this would also work fine:
> > > >
> > > > proc ui_do_rescan {} {
> > > > rescan ui_ready
> > > > prime_gitdir_cache
> > > > }
> > >
> > > That was my first attempt. However, there is a very important piece of
> > > code that is even still quoted above: that `if {$rescan_active > 0 ||
> > > ![lock_index read]} return` part.
> > >
> > > I do _not_ want to interfere with an actively-going-on rescan. If there
> > > is an active one, I don't want to re-prime the `_gitdir` cache.
> >
> > Good catch! In that case I suppose refreshing the cache in $after would
> > be the way to go (IOW, the former of my two suggestions). Anything
> > $after won't get executed if we return early from that check.
>
> The obvious problem with that solution is that the `_gitdir` is reset
> _after_ the rescan. In my solution, it is reset _before_, as I have no
> idea how often the `_gitdir` values are used during a rescan (and if
> none of they were, I would like to be very cautious to prepare for a
> future where any of those `_gitdir` values _are_ used during a rescan).
_gitdir values are used quite often during a rescan, so yes, this won't
work.
> So I am afraid that I find way too serious problems with both of your
> proposed alternatives.
One alternative I can see right now is adding another optional parameter
to `rescan` that controls whether we refresh the gitdir cache or not.
That parameter would default to 0/false. I'm not the biggest fan of
something like this, but it might be the easiest way to do it given the
constraints.
I also thought about trying to acquire the index lock in
`prime_gitdir_cache`, but that could create a race on the lock between
`prime_gitdir_cache` and `rescan`.
If you have any better ideas, I'm all ears, but otherwise, I maybe our
best bet is to just go with adding an optional parameter to `rescan`.
--
Regards,
Pratyush Yadav
