On Mon, Aug 16, 2021 at 11:32 AM Matheus Tavares Bernardino <matheus.bernardino@xxxxxx> wrote: > > On Fri, Aug 13, 2021 at 6:05 PM Jonathan Tan <jonathantanmy@xxxxxxxxxx> wrote: > > > > When reading the config of a submodule, if reading from a blob, read > > using an explicitly specified repository instead of by adding the > > submodule's ODB as an alternate and then reading an object from > > the_repository. > > Great! > > At first, I thought this would also allow us to remove another > NEEDSWORK comment in grep_submodule(), together with a lock > protection: > > /* > * NEEDSWORK: repo_read_gitmodules() might call > * add_to_alternates_memory() via config_from_gitmodules(). This > * operation causes a race condition with concurrent object readings > * performed by the worker threads. That's why we need obj_read_lock() > * here. It should be removed once it's no longer necessary to add the > * subrepo's odbs to the in-memory alternates list. > */ > obj_read_lock(); > repo_read_gitmodules(subrepo, 0); > > Back when I wrote this comment, my conclusion was that the alternates > mechanics were the only thread-unsafe object-reading operations in > repo_read_gitmodules()'s call chains. So once the add-to-alternates > mechanics were gone, we could also remove the lock. > > But with further inspection now, I see that this is not really the > case. For example, we have a few global variables in packfile.c > collecting some statistics (pack_mmap_calls, pack_open_windows, etc.) > which are updated on obj readings from both the_repository *and* > submodules. Sorry, this is incorrect. I forgot that repo_read_object_file() (which is part of repo_read_gitmodules()'s call chain) also acquires the obj_read_mutex before accessing those global variables. So the NEEDSWORK might be right. Nevertheless, I think it might be better to look into repo_read_gitmodules() more carefully before removing this lock. And this is something for another series. Sorry about the noise.
