[ltt-dev] [UST PATCH] TESTS: Add a delay at the start of the fork test for a more uniform testing.

Nils Carlson nils.carlson at ericsson.com
Tue Feb 22 10:54:39 EST 2011

Yannick Brosseau wrote:
> On 2011-02-22 03:28, Nils Carlson wrote:
>> Yannick Brosseau wrote:
>>> Add a sleep to leave time for the ustconsumer thread to initialize
>>> correctly
>>> before the fork.
>>> Most of the time the consumer was not yet started at the time of the
>>> fork so
>>> a bunch of initializations were not done and the fork code path was not
>>> tested properly.
>> I'm afraid we're falling into a bit of a trap here. The trap is called
>> "fixing the test-case instead of fixing the code". It's quite typical
> No that's not the case here. I'm fixing the test case, so it shows us a
> problem that was occuring randomly before.
> With my "fix" to the test case, the test case will fail all the time and
> showing us the problem when we fork later. (Some application do it, so
> UST should not fail there)
So you're saying that this causes the test case to fail all the time 
because now we leave time for things to properly initialise, while if we 
don't initialise things sometimes work?
I think I understand what you mean but I still don't agree. What about 
making sure somehow that we are fully initialized before we hit main()? 
In the case where we are tracing from startup using usttrace we should 
in fact be fully initialised before we allow the program to enter main.

If you don't think we should be fully initialized before entering main() 
please explain why.

> I could duplicate the test case with one doing an early fork and one
> doing a late fork. I did not do it, because there was no problem to the
> early fork.
> The fix to the problem is my other email.
>> for an application to fork right after startup. In fact, this is probably
>> by far the most common place where applications fork when going into a
>> daemon
>> mode. So we should probably focus on fixing the problem instead,
>> probably by
>> detecting that we are following forks with UST and if we are somehow
>> slowing
>> down the initialisation functions so that everything has started up
>> properly
>> by the time we enter main().
>> /Nils
>>> Signed-off-by: Yannick Brosseau <yannick.brosseau at gmail.com>
>>> ---
>>>  tests/fork/fork.c |    3 +++
>>>  1 files changed, 3 insertions(+), 0 deletions(-)
>>> diff --git a/tests/fork/fork.c b/tests/fork/fork.c
>>> index 5ce3d6d..a80518d 100644
>>> --- a/tests/fork/fork.c
>>> +++ b/tests/fork/fork.c
>>> @@ -34,6 +34,9 @@ int main(int argc, char **argv, char *env[])
>>>      printf("Fork test program, parent pid is %d\n", getpid());
>>>      trace_mark(ust, before_fork, MARK_NOARGS);
>>> +    /* Sleep here to make sure the consumer is initialized before we
>>> fork */
>>> +    sleep(1);
>>> +
>>>      result = fork();
>>>      if(result == -1) {
>>>          perror("fork");

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