[yocto] [ptest-runner] utils.c: Prefer monotonic clock to calculate elapsed time

[Joshua Lock]

On 31/10/17 19:38, Jeffrey Pautler wrote:
> The current implementation uses the system clock to calculate how long
> a ptest has been running with no output. If a ptest changes the system
> clock as part of the test, that can cause the current implementation
> to falsely trigger a timeout or miss an actual timeout. It is
> preferrable to use a monotonic clock for calculating elapsed time in
> order to avoid these issues.
> 
> This change tries to use the monotonic clock first and falls back to
> the realtime clock if the monotonic clock is not supported.

This patch looks good to me, merged & pushed to ptest-runner2 repo.

Thanks,

Joshua

> 
> Signed-off-by: Jeffrey Pautler <jeffrey.pautler at ni.com>
> ---
>   utils.c | 24 +++++++++++++++++-------
>   1 file changed, 17 insertions(+), 7 deletions(-)
> 
> diff --git a/utils.c b/utils.c
> index 6d65388..933eced 100644
> --- a/utils.c
> +++ b/utils.c
> @@ -257,7 +257,8 @@ wait_child(const char *ptest_dir, const char *run_ptest, pid_t pid,
>   		int timeout, int *fds, FILE **fps)
>   {
>   	struct pollfd pfds[2];
> -	time_t sentinel;
> +	struct timespec sentinel;
> +	clockid_t clock = CLOCK_MONOTONIC;
>   	int r;
>   
>   	int timeouted = 0;
> @@ -269,7 +270,11 @@ wait_child(const char *ptest_dir, const char *run_ptest, pid_t pid,
>   	pfds[1].fd = fds[1];
>   	pfds[1].events = POLLIN;
>   
> -	sentinel = time(NULL);
> +	if (clock_gettime(clock, &sentinel) == -1) {
> +		clock = CLOCK_REALTIME;
> +		clock_gettime(clock, &sentinel);
> +	}
> +
>   	while (1) {
>   		waitflags = WNOHANG;
>   
> @@ -288,11 +293,16 @@ wait_child(const char *ptest_dir, const char *run_ptest, pid_t pid,
>   					fwrite(buf, n, 1, fps[1]);
>   			}
>   
> -			sentinel = time(NULL);
> -		} else if (timeout >= 0 && ((time(NULL) - sentinel) > timeout)) {
> -			timeouted = 1;
> -			kill(pid, SIGKILL);
> -			waitflags = 0;
> +			clock_gettime(clock, &sentinel);
> +		} else if (timeout >= 0) {
> +			struct timespec time;
> +
> +			clock_gettime(clock, &time);
> +			if ((time.tv_sec - sentinel.tv_sec) > timeout) {
> +				timeouted = 1;
> +				kill(pid, SIGKILL);
> +				waitflags = 0;
> +			}
>   		}
>   
>   		if (waitpid(pid, &status, waitflags) == pid)
>