| Message ID | 1a0a3eebb825ac3eabfdd86f82ed7ef6abb454c5.1600366313.git.gitgitgadget@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | d7514f6ed57d20bcc9dcfb43016b95dba82ba790 |
| Headers | show |
| Series | Maintenance I: Command, gc and commit-graph tasks | expand |
On Thu, Sep 17 2020, Derrick Stolee via GitGitGadget wrote: > From: Derrick Stolee <dstolee@microsoft.com> > > Performing maintenance on a Git repository involves writing data to the > .git directory, which is not safe to do with multiple writers attempting > the same operation. Ensure that only one 'git maintenance' process is > running at a time by holding a file-based lock. Simply the presence of > the .git/maintenance.lock file will prevent future maintenance. This > lock is never committed, since it does not represent meaningful data. > Instead, it is only a placeholder. > > If the lock file already exists, then no maintenance tasks are > attempted. This will become very important later when we implement the > 'prefetch' task, as this is our stop-gap from creating a recursive process > loop between 'git fetch' and 'git maintenance run --auto'. > > Signed-off-by: Derrick Stolee <dstolee@microsoft.com> > Signed-off-by: Junio C Hamano <gitster@pobox.com> > --- > builtin/gc.c | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/builtin/gc.c b/builtin/gc.c > index 00fff59bdb..7ba9c6f7c9 100644 > --- a/builtin/gc.c > +++ b/builtin/gc.c > @@ -798,6 +798,25 @@ static int maintenance_run_tasks(struct maintenance_run_opts *opts) > { > int i, found_selected = 0; > int result = 0; > + struct lock_file lk; > + struct repository *r = the_repository; > + char *lock_path = xstrfmt("%s/maintenance", r->objects->odb->path); > + > + if (hold_lock_file_for_update(&lk, lock_path, LOCK_NO_DEREF) < 0) { > + /* > + * Another maintenance command is running. > + * > + * If --auto was provided, then it is likely due to a > + * recursive process stack. Do not report an error in > + * that case. > + */ > + if (!opts->auto_flag && !opts->quiet) > + warning(_("lock file '%s' exists, skipping maintenance"), > + lock_path); > + free(lock_path); > + return 0; > + } > + free(lock_path); > > for (i = 0; !found_selected && i < TASK__COUNT; i++) > found_selected = tasks[i].selected_order >= 0; There's now two different lock strategies in builtin/gc.c, the existing one introduced in 64a99eb476 ("gc: reject if another gc is running, unless --force is given", 2013-08-08) where we write the hostname to the gc.pid file, and then discard the lockfile depending on a heuristic of whether or not it's the same etc., and this one. With this as an entry point we'll entirely do away with the old one since we don't use the "gc --auto" entry point. All of that may or may not be desirable, but I think a description in the docs & tests for how these lock files should interact would be helpful. E.g. writing a different hostname in the gc lockfile and setting the time on it with with "test-tool chmtime" will cause it to plow ahead, but doing the same for "git maintenance" will stop it in its tracks no matter the time or content.
On 9/21/2020 9:36 AM, Ævar Arnfjörð Bjarmason wrote: > There's now two different lock strategies in builtin/gc.c, the existing > one introduced in 64a99eb476 ("gc: reject if another gc is running, > unless --force is given", 2013-08-08) where we write the hostname to the > gc.pid file, and then discard the lockfile depending on a heuristic of > whether or not it's the same etc., and this one. > > With this as an entry point we'll entirely do away with the old one > since we don't use the "gc --auto" entry point. Users could still erroneously launch two `git gc` commands concurrently and that will not use the maintenance.lock file. The GC lock is worth keeping around until we redirect the `gc` command to be an alias that runs `git maintenance run --task=gc [options]`. > All of that may or may not be desirable, but I think a description in > the docs & tests for how these lock files should interact would be > helpful. E.g. writing a different hostname in the gc lockfile and > setting the time on it with with "test-tool chmtime" will cause it to > plow ahead, but doing the same for "git maintenance" will stop it in its > tracks no matter the time or content. Thanks for the pointers to create this test. I'll try to get to it soon. For now, here is a tracking issue [1]. [1] https://github.com/gitgitgadget/git/issues/737 Thanks, -Stolee
Derrick Stolee <stolee@gmail.com> writes: >> With this as an entry point we'll entirely do away with the old one >> since we don't use the "gc --auto" entry point. > > Users could still erroneously launch two `git gc` commands concurrently > and that will not use the maintenance.lock file. The GC lock is worth > keeping around until we redirect the `gc` command to be an alias that > runs `git maintenance run --task=gc [options]`. Yes, that is prudent. And as long as the traditional gc lock stops the maintenance command from running the gc task, everthing would work consistently ;-) Thanks.
diff --git a/builtin/gc.c b/builtin/gc.c index 00fff59bdb..7ba9c6f7c9 100644 --- a/builtin/gc.c +++ b/builtin/gc.c @@ -798,6 +798,25 @@ static int maintenance_run_tasks(struct maintenance_run_opts *opts) { int i, found_selected = 0; int result = 0; + struct lock_file lk; + struct repository *r = the_repository; + char *lock_path = xstrfmt("%s/maintenance", r->objects->odb->path); + + if (hold_lock_file_for_update(&lk, lock_path, LOCK_NO_DEREF) < 0) { + /* + * Another maintenance command is running. + * + * If --auto was provided, then it is likely due to a + * recursive process stack. Do not report an error in + * that case. + */ + if (!opts->auto_flag && !opts->quiet) + warning(_("lock file '%s' exists, skipping maintenance"), + lock_path); + free(lock_path); + return 0; + } + free(lock_path); for (i = 0; !found_selected && i < TASK__COUNT; i++) found_selected = tasks[i].selected_order >= 0; @@ -818,6 +837,7 @@ static int maintenance_run_tasks(struct maintenance_run_opts *opts) } } + rollback_lock_file(&lk); return result; }