[lttng-dev] [PATCH lttng-tools] Fix: mi test: possible race between listing UST events and testapp start

[Jonathan Rajotte]

Hey

On Mon, Oct 27, 2014 at 4:48 PM, Nathan Lynch <Nathan_Lynch at mentor.com>
wrote:

> On 10/26/2014 08:21 PM, Jonathan Rajotte wrote:
> > Signed-off-by: Jonathan Rajotte <jonathan.r.julien at gmail.com>
>
> More description of the change is needed IMO.
>
> > ---
> >  tests/regression/tools/mi/test_mi | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/tests/regression/tools/mi/test_mi
> b/tests/regression/tools/mi/test_mi
> > index fa46b51..7acec18 100755
> > --- a/tests/regression/tools/mi/test_mi
> > +++ b/tests/regression/tools/mi/test_mi
> > @@ -507,6 +507,11 @@ function test_list_ust_event ()
> >
> >       #Begin testing
> >       $TESTAPP_BIN $NR_USEC_WAIT & 2>/dev/null
> > +     pid=$!
> > +
> > +     #Wait for TESTAPP to run
> > +     while ! kill -0 $pid 2> /dev/null; do :; done
> > +
> >       list_lttng_with_opts "-u -f"
>
> Is this an attempt to give the test program enough time to register
> tracepoints?
>

A poor one... if one at all.... for which I needed feedback (missing rfc
tag here) because I could not simply find any simple way. See [1]


> If so, I agree there is a race, but I don't think this is the right way
> to address it.

   I would not expect the while ! kill loop to repeat at

> all;


The presence of ":" assure the execution of the while loop.
A simple test on a process that does not exist yield a lot of printing:

while ! kill -0 500; do :; done

Anyway it does not solve the problem. ;) and I'm not sure you were talking
about that.

if you remove the stderr redirection do you see any output, ever?

The exit status from kill $! is not a reliable indication that the shell
> has execve'd the program in the background, and even if it were, it
> would not be a reliable indication of how far the program has progressed


+1

(e.g. whether it has got far enough along to register tracepoints).
>
>

> If a test program needs to run in the background, yet needs to reach a
> certain state before the rest of the test should proceed, then it should
> have a way to indicate to the test harness that it has reached the
> desired state.  The shell's rudimentary facilities for managing
> concurrency are not sufficient.
>

I'm pushing limits here regarding simplicity: how about a trap and signal
exchange between the testapp... might give it a shot. Or a simple sleep...

Thanks, I'll think about it a little more.

[1]:http://meta.wikimedia.org/wiki/Cunningham%27s_Law
Bonus xkcd: http://xkcd.com/386/
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