The progress.c code makes a hard assumption that only one progress bar
be active at a time (see [1] for a bug where this wasn't the
case). Add a BUG() that'll trigger if we ever regress on that promise
and have two progress bars active at the same time.
There was an alternative test-only approach to doing the same
thing[2], but by doing this outside of a GIT_TEST_* mode we'll know
we've put a hard stop to this particular API misuse.
It will also establish scaffolding to address current fundamental
limitations in the progress output: The current output must be
"driven" by calls to the likes of display_progress(). Once we have a
global current progress object we'll be able to update that object via
SIGALRM. See [3] for early code to do that.
It's conceivable that this change will hit the BUG() condition in some
scenario that we don't currently have tests for, this would be very
bad. If that happened we'd die just because we couldn't emit some
pretty output.
See [4] for a discussion of why our test coverage is lacking; our
progress display is hidden behind isatty(2) checks in many cases, so
the test suite doesn't cover it unless individual tests are run in
"--verbose" mode, we might also have multi-threaded use of the API, so
two progress bars stopping and starting would only be visible due to a
race condition.
Despite that, I think that this change won't introduce such
regressions, because:
1. I've read all the code using the progress API (and have modified a
large part of it in some WIP code I have). Almost all of it is really
simple, the parts that aren't[5] are complex in the display_progress() part,
not in starting or stopping the progress bar.
2. The entire test suite passes when instrumented with an ad-hoc
Linux-specific mode (it uses gettid()) to die if progress bars are
ever started or stopped on anything but the main thread[6].
Extending that to die if display_progress() is called in a thread
reveals that we have exactly two users of the progress bar under
threaded conditions, "git index-pack" and "git pack-objects". Both
uses are straightforward, and they don't start/stop the progress
bar when threads are active.
3. I've likewise done an ad-hoc test to force progress bars to be
displayed with:
perl -pi -e 's[isatty\((?:STDERR_FILENO|2)\)][1]g' $(git grep -l 'isatty\((STDERR_FILENO|2)\)')
I.e. to replace all checks (not just for progress) of checking
whether STDERR is connected to a TTY, and then monkeypatching
is_foreground_fd() in progress.c to always "return 1". Running the
tests with those applied, interactively and under -V reveals via:
$ grep -e set_progress_signal -e clear_progress_signal test-results/*out
That nothing our tests cover hits the BUG conditions added here,
except the expected "BUG: start two concurrent progress bars" test
being added here.
That isn't entirely true since we won't be getting 100% coverage
due to cascading failures from tests that expected no progress
output on stderr. To make sure I covered 100% I also tried making
the display() function in progress.c a NOOP on top of that (it's
the calls to start_progress_delay() and stop_progress()) that
matter.
That doesn't hit the BUG() either. Some tests fail in that mode
due to a combination of the overzealous isatty(2) munging noted
above, and the tests that are testing that the progress output
itself is present (but for testing I'd made display() a NOOP).
Between those three points I think it's safe to go ahead with this
change.
1. 6f9d5f2fda1 (commit-graph: fix progress of reachable commits, 2020-07-09)
2. https://lore.kernel.org/git/20210620200303.2328957-3-szeder.dev@xxxxxxxxx
3. https://lore.kernel.org/git/patch-18.25-e21fc66623f-20210623T155626Z-avarab@xxxxxxxxx/
4. https://lore.kernel.org/git/cover-00.25-00000000000-20210623T155626Z-avarab@xxxxxxxxx/
5. b50c37aa44d (Merge branch 'ab/progress-users-adjust-counters' into
next, 2021-09-10)
6. https://lore.kernel.org/git/877dffg37n.fsf@xxxxxxxxxxxxxxxxxxx/
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
---
progress.c | 17 +++++++++++++----
t/t0500-progress-display.sh | 11 +++++++++++
2 files changed, 24 insertions(+), 4 deletions(-)
diff --git a/progress.c b/progress.c
index 1ab7d19deb8..14a023f4b43 100644
--- a/progress.c
+++ b/progress.c
@@ -46,6 +46,7 @@ struct progress {
};
static volatile sig_atomic_t progress_update;
+static struct progress *global_progress;
/*
* These are only intended for testing the progress output, i.e. exclusively
@@ -221,11 +222,15 @@ void progress_test_force_update(void)
progress_interval(SIGALRM);
}
-static void set_progress_signal(void)
+static void set_progress_signal(struct progress *progress)
{
struct sigaction sa;
struct itimerval v;
+ if (global_progress)
+ BUG("should have no global_progress in set_progress_signal()");
+ global_progress = progress;
+
if (progress_testing)
return;
@@ -243,10 +248,14 @@ static void set_progress_signal(void)
setitimer(ITIMER_REAL, &v, NULL);
}
-static void clear_progress_signal(void)
+static void clear_progress_signal(struct progress *progress)
{
struct itimerval v = {{0,},};
+ if (!global_progress)
+ BUG("should have a global_progress in clear_progress_signal()");
+ global_progress = NULL;
+
if (progress_testing)
return;
@@ -270,7 +279,7 @@ static struct progress *start_progress_delay(const char *title, uint64_t total,
strbuf_init(&progress->counters_sb, 0);
progress->title_len = utf8_strwidth(title);
progress->split = 0;
- set_progress_signal();
+ set_progress_signal(progress);
trace2_region_enter("progress", title, the_repository);
return progress;
}
@@ -374,7 +383,7 @@ void stop_progress_msg(struct progress **p_progress, const char *msg)
display(progress, progress->last_value, buf);
free(buf);
}
- clear_progress_signal();
+ clear_progress_signal(progress);
strbuf_release(&progress->counters_sb);
if (progress->throughput)
strbuf_release(&progress->throughput->display);
diff --git a/t/t0500-progress-display.sh b/t/t0500-progress-display.sh
index ffa819ca1db..124d33c96b3 100755
--- a/t/t0500-progress-display.sh
+++ b/t/t0500-progress-display.sh
@@ -296,6 +296,17 @@ test_expect_success 'cover up after throughput shortens a lot' '
test_cmp expect out
'
+test_expect_success 'BUG: start two concurrent progress bars' '
+ cat >in <<-\EOF &&
+ start 0 one
+ start 0 two
+ EOF
+
+ test_must_fail test-tool progress \
+ <in 2>stderr &&
+ grep -E "^BUG: .*: should have no global_progress in set_progress_signal\(\)$" stderr
+'
+
test_expect_success 'progress generates traces' '
cat >in <<-\EOF &&
start 40
--
2.33.0.1098.gf02a64c1a2d
