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[2a01:4f8:120:2468::2]) by smtp.gmail.com with ESMTPSA id l5sm736683wrq.77.2021.10.13.15.28.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Oct 2021 15:28:35 -0700 (PDT) From: =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?= To: git@vger.kernel.org Cc: Junio C Hamano , =?UTF-8?q?SZEDER=20G=C3=A1bor?= , =?UTF-8?q?Ren=C3=A9=20Scharfe?= , Emily Shaffer , =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?= Subject: [PATCH v3 10/10] progress.c: add & assert a "global_progress" variable Date: Thu, 14 Oct 2021 00:28:26 +0200 Message-Id: X-Mailer: git-send-email 2.33.1.1346.g48288c3c089 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org 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\(2\)][1]g' $(git grep -l -F 'isatty(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@gmail.com 3. https://lore.kernel.org/git/patch-18.25-e21fc66623f-20210623T155626Z-avarab@gmail.com/ 4. https://lore.kernel.org/git/cover-00.25-00000000000-20210623T155626Z-avarab@gmail.com/ 5. b50c37aa44d (Merge branch 'ab/progress-users-adjust-counters' into next, 2021-09-10) 6. https://lore.kernel.org/git/877dffg37n.fsf@evledraar.gmail.com/ Signed-off-by: Ævar Arnfjörð Bjarmason --- progress.c | 18 ++++++++++++++---- t/t0500-progress-display.sh | 11 +++++++++++ 2 files changed, 25 insertions(+), 4 deletions(-) diff --git a/progress.c b/progress.c index b9369e9a264..a31500f8b2b 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 @@ -219,11 +220,16 @@ 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("'%s' progress still active when trying to start '%s'", + global_progress->title, progress->title); + global_progress = progress; + if (progress_testing) return; @@ -241,10 +247,14 @@ 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 active global_progress when cleaning up"); + global_progress = NULL; + if (progress_testing) return; @@ -268,7 +278,7 @@ 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; } @@ -372,7 +382,7 @@ 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 59e9f226ea4..867fdace3f2 100755 --- a/t/t0500-progress-display.sh +++ b/t/t0500-progress-display.sh @@ -298,6 +298,17 @@ 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 \ + stderr && + grep "^BUG: .*'\''one'\'' progress still active when trying to start '\''two'\''$" stderr +' + test_expect_success 'progress generates traces' ' cat >in <<-\EOF && start 40 -- 2.33.1.1346.g48288c3c089