Re: [PATCH] t4053: avoid race when killing background processes

[Phillip Wood <phillip.wood123@gmail.com>]

On 10/08/2023 18:40, Junio C Hamano wrote:
> "Phillip Wood via GitGitGadget" <gitgitgadget@gmail.com> writes:
 >
> While I can see that "kill" in the when-finished handler may or may
> not find the backgrounded process by the time it is run, and
> ignoring its exit status (hence keeping test_when_finished happy)
> would be a reasonable thing to do.  I can understand if this patch
> is to fix a different symptom, namely, when-finished handler
> sometimes fails and makes the test fail.
> 
> But I am not sure how this causes the test to "hang", 


This is only a fix for the test failure that Peff saw when running with 
--stress.

> which
> presumably is a symptom that somebody is trying to read from
> a pipe that nobody is making progress to write into?

That or a process blocking when tying to open a fifo seems the mostly 
likely cause but I can't see where that is happening. As you say this 
patch does not obviously change anything that would be causing the test 
to hang.

Best Wishes

Phillip

>  We will
> send a signal either way to the writers, and the only difference is
> that we ignore the exit code.
> 
> Granted, when-finished handlers are concatenated with "&&-", and one
> "kill"s failure will cause the other "kill" not to run, so we may
> send a signal to only one but not to the other, but that should all
> happen after "diff --no-index" returns, so it still does not explain
> the "hang".
> 
> Puzzled...

>> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1571%2Fphillipwood%2Fdiff-no-index-pipes-fixes-v1
>> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1571/phillipwood/diff-no-index-pipes-fixes-v1
>> Pull-Request: https://github.com/gitgitgadget/git/pull/1571
>>
>>   t/t4053-diff-no-index.sh | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/t/t4053-diff-no-index.sh b/t/t4053-diff-no-index.sh
>> index a28b9ff2434..1fb7d334620 100755
>> --- a/t/t4053-diff-no-index.sh
>> +++ b/t/t4053-diff-no-index.sh
>> @@ -248,11 +248,11 @@ test_expect_success PIPE,SYMLINKS 'diff --no-index reads from pipes' '
>>   	{
>>   		(test_write_lines a b c >old) &
>>   	} &&
>> -	test_when_finished "! kill $!" &&
>> +	test_when_finished "kill $! || :" &&
>>   	{
>>   		(test_write_lines a x c >new) &
>>   	} &&
>> -	test_when_finished "! kill $!" &&
>> +	test_when_finished "kill $! || :" &&
>>   
>>   	cat >expect <<-EOF &&
>>   	diff --git a/old b/new-link
>>
>> base-commit: a82fb66fed250e16d3010c75404503bea3f0ab61