[DTrace-devel] [PATCH v2] test: Wait for output to flush out in enable_pid

[Kris Van Hees]

I still see intermittent FAILs.  I wonder whether there is a potentially unsafe
contruct at work (see below).

On Sat, Jun 28, 2025 at 06:30:50PM -0400, eugene.loh at oracle.com wrote:
> From: Eugene Loh <eugene.loh at oracle.com>
> 
> Our luck with this test has been quite good, but it sometimes fails
> to show its last lines of output.  That is, we send a USR1 to the
> trigger processes to set off the final output and we immediately
> cat the output files.  If there is any delay in handling the signal,
> the last output will be missing.
> 
> Have the processes terminate themselves when their last output is
> flushed; then wait for those processes.  Also, skip testing altogether if
> there is only a single processor to run the two, hard-spinning processes.
> 
> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
> ---
>  test/unittest/usdt/tst.enable_pid.sh | 17 ++++++++++++-----
>  test/unittest/usdt/tst.enable_pid.x  |  8 ++++++++
>  2 files changed, 20 insertions(+), 5 deletions(-)
>  create mode 100755 test/unittest/usdt/tst.enable_pid.x
> 
> diff --git a/test/unittest/usdt/tst.enable_pid.sh b/test/unittest/usdt/tst.enable_pid.sh
> index 7f4f68698..296cfb382 100755
> --- a/test/unittest/usdt/tst.enable_pid.sh
> +++ b/test/unittest/usdt/tst.enable_pid.sh
> @@ -33,6 +33,8 @@ EOF
>  cat > main.c <<EOF
>  #include <signal.h>
>  #include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
>  #include "prov.h"
>  
>  /* We check if the is-enabled probe is or is not enabled (or unknown). */
> @@ -41,7 +43,7 @@ cat > main.c <<EOF
>  #define ENABLED_UNK	3
>  
>  /* Start with the previous probe "unknown". */
> -int prv = ENABLED_UNK;
> +int prv = ENABLED_UNK, nepochs_left = 4;
>  long long num = 0;
>  
>  /* Report how many times the previous case was encountered. */
> @@ -71,6 +73,9 @@ static void mark_epoch(int sig) {
>  	report();
>  	printf("=== epoch ===\n");
>  	fflush(stdout);
> +	nepochs_left--;
> +	if (nepochs_left <= 0)
> +		exit(0);

I wonder whether this could still cause some output to get lost.  I would
actually move the conditional and exit to the end of the loop in main(),
so that we check nepochs_left and exit when <= 0 outside of the interrupt
handler.

I am running a long sequence of this test to see if that helps/fixes it.

>  }
>  
>  int
> @@ -79,7 +84,7 @@ main(int argc, char **argv)
>  	struct sigaction act;
>  
>  	/* Set USR1 to mark epochs. */
> -	act.sa_flags = 0;
> +	memset(&act, 0, sizeof(act));
>  	act.sa_handler = mark_epoch;
>  	if (sigaction(SIGUSR1, &act, NULL)) {
>  		printf("set handler failed\n");
> @@ -172,13 +177,15 @@ for pid in 1 $pid1 $pid2 '*'; do
>  	kill -USR1 $pid2
>  done
>  
> +# Wait for the processes.
> +wait $pid1
> +wait $pid2
> +
> +# Dump the output.
>  echo done
>  echo "========== out 1"; cat out.1
>  echo "========== out 2"; cat out.2
>  
>  echo success
>  
> -kill -TERM $pid1
> -kill -TERM $pid2
> -
>  exit 0
> diff --git a/test/unittest/usdt/tst.enable_pid.x b/test/unittest/usdt/tst.enable_pid.x
> new file mode 100755
> index 000000000..9506674ee
> --- /dev/null
> +++ b/test/unittest/usdt/tst.enable_pid.x
> @@ -0,0 +1,8 @@
> +#!/bin/sh
> +
> +if [ `grep -c ^processor /proc/cpuinfo` -lt 2 ]; then
> +	echo test should have at least two processors
> +	exit 2
> +fi
> +
> +exit 0
> -- 
> 2.43.5
>