On Wed, May 18, 2022 at 10:05:24PM +0200, Ævar Arnfjörð Bjarmason wrote:
>
> Fix a regression reported[1] in f443246b9f2 (commit: convert
> {pre-commit,prepare-commit-msg} hook to hook.h, 2021-12-22): Due to
> using the run_process_parallel() API in the earlier 96e7225b310 (hook:
> add 'run' subcommand, 2021-12-22) we'd capture the hook's stderr and
> stdout, and thus lose the connection to the TTY in the case of
> e.g. the "pre-commit" hook.
>
> As a preceding commit notes GNU parallel's similar --ungroup option
> also has it emit output faster. While we're unlikely to have hooks
> that emit truly massive amounts of output (or where the performance
> thereof matters) it's still informative to measure the overhead. In a
> similar "seq" test we're now ~30% faster:
>
> $ cat .git/hooks/seq-hook; git hyperfine -L rev origin/master,HEAD~0 -s 'make CFLAGS=-O3' './git hook run seq-hook'
> #!/bin/sh
>
> seq 100000000
> Benchmark 1: ./git hook run seq-hook' in 'origin/master
> Time (mean ± σ): 787.1 ms ± 13.6 ms [User: 701.6 ms, System: 534.4 ms]
> Range (min … max): 773.2 ms … 806.3 ms 10 runs
>
> Benchmark 2: ./git hook run seq-hook' in 'HEAD~0
> Time (mean ± σ): 603.4 ms ± 1.6 ms [User: 573.1 ms, System: 30.3 ms]
> Range (min … max): 601.0 ms … 606.2 ms 10 runs
>
> Summary
> './git hook run seq-hook' in 'HEAD~0' ran
> 1.30 ± 0.02 times faster than './git hook run seq-hook' in 'origin/master'
>
> In the preceding commit we removed the "stdout_to_stderr=1" assignment
> as being redundant. This change brings it back as with ".ungroup=1"
> the run_process_parallel() function doesn't provide them for us
> implicitly.
>
> As an aside omitting the stdout_to_stderr=1 here would have all tests
> pass, except those that test "git hook run" itself in
> t1800-hook.sh. But our tests passing is the result of another test
> blind spot, as was the case with the regression being fixed here. The
> "stdout_to_stderr=1" for hooks is long-standing behavior, see
> e.g. 1d9e8b56fe3 (Split back out update_hook handling in receive-pack,
> 2007-03-10) and other follow-up commits (running "git log" with
> "--reverse -p -Gstdout_to_stderr" is a good start).
>
> 1. https://lore.kernel.org/git/CA+dzEBn108QoMA28f0nC8K21XT+Afua0V2Qv8XkR8rAeqUCCZw@xxxxxxxxxxxxxx/
>
> Reported-by: Anthony Sottile <asottile@xxxxxxxxx>
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
> ---
> hook.c | 5 +++++
> t/t1800-hook.sh | 37 +++++++++++++++++++++++++++++++++++++
> 2 files changed, 42 insertions(+)
>
> diff --git a/hook.c b/hook.c
> index dc498ef5c39..5f31b60384a 100644
> --- a/hook.c
> +++ b/hook.c
> @@ -54,6 +54,7 @@ static int pick_next_hook(struct child_process *cp,
> return 0;
>
> strvec_pushv(&cp->env_array, hook_cb->options->env.v);
> + cp->stdout_to_stderr = 1; /* because of .ungroup = 1 */
> cp->trace2_hook_name = hook_cb->hook_name;
> cp->dir = hook_cb->options->dir;
>
> @@ -126,6 +127,7 @@ int run_hooks_opt(const char *hook_name, struct run_hooks_opt *options)
> .tr2_label = hook_name,
>
> .jobs = jobs,
> + .ungroup = jobs == 1,
I mentioned it on patch 5, but I actually do not see a reason why we
shouldn't do this logic in run_processes_parallel instead of just for
the hooks. If someone can mention a reason we want to buffer child
processes we're running in series I'm all ears, of course.
>
> .get_next_task = pick_next_hook,
> .start_failure = notify_start_failure,
> @@ -136,6 +138,9 @@ int run_hooks_opt(const char *hook_name, struct run_hooks_opt *options)
> if (!options)
> BUG("a struct run_hooks_opt must be provided to run_hooks");
>
> + if (jobs != 1 || !run_opts.ungroup)
> + BUG("TODO: think about & document order & interleaving of parallel hook output");
Doesn't this mean we're actually disallowing parallel hooks entirely? I
don't think that's necessary or desired. I guess right now when the
config isn't used, there's not really a way to provide parallel hooks,
but I also think this will cause unnecessary conflicts for Google who is
carrying config hooks downstream. I know that's not such a great reason.
But it seems weird to be explicitly using the parallel processing
framework, but then say, "oh, but we actually don't want to run in
parallel, that's a BUG()".
> +
> if (options->invoked_hook)
> *options->invoked_hook = 0;
>
> diff --git a/t/t1800-hook.sh b/t/t1800-hook.sh
> index 1e4adc3d53e..f22754deccc 100755
> --- a/t/t1800-hook.sh
> +++ b/t/t1800-hook.sh
> @@ -4,6 +4,7 @@ test_description='git-hook command'
>
> TEST_PASSES_SANITIZE_LEAK=true
> . ./test-lib.sh
> +. "$TEST_DIRECTORY"/lib-terminal.sh
>
> test_expect_success 'git hook usage' '
> test_expect_code 129 git hook &&
> @@ -120,4 +121,40 @@ test_expect_success 'git -c core.hooksPath=<PATH> hook run' '
> test_cmp expect actual
> '
>
> +test_hook_tty() {
> + local fd="$1" &&
> +
> + cat >expect &&
> +
> + test_when_finished "rm -rf repo" &&
> + git init repo &&
> +
> + test_hook -C repo pre-commit <<-EOF &&
> + {
> + test -t 1 && echo >&$fd STDOUT TTY || echo >&$fd STDOUT NO TTY &&
> + test -t 2 && echo >&$fd STDERR TTY || echo >&$fd STDERR NO TTY
> + } $fd>actual
> + EOF
> +
> + test_commit -C repo A &&
> + test_commit -C repo B &&
> + git -C repo reset --soft HEAD^ &&
> + test_terminal git -C repo commit -m"B.new" &&
> + test_cmp expect repo/actual
> +}
> +
> +test_expect_success TTY 'git hook run: stdout and stderr are connected to a TTY: STDOUT redirect' '
> + test_hook_tty 1 <<-\EOF
> + STDOUT NO TTY
> + STDERR TTY
> + EOF
> +'
> +
> +test_expect_success TTY 'git hook run: stdout and stderr are connected to a TTY: STDERR redirect' '
> + test_hook_tty 2 <<-\EOF
> + STDOUT TTY
> + STDERR NO TTY
> + EOF
> +'
> +
> test_done
> --
> 2.36.1.952.g0ae626f6cd7
>
