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

Nathan Lynch Nathan_Lynch at mentor.com
Mon Oct 27 16:48:15 EDT 2014

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

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; 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
(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.

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