On Thu, Aug 09, 2012 at 03:35:49PM +0100, Rob Bradford wrote:
> From: Rob Bradford <[email protected]>
>
> To handle the case where wall clock time jumps forwards by a large amount or
> backwards limit the execution of the spring calculation loop.
>
> We do this by forcing the spring update timestamp to being no older that 1s of
> the most current time we've been given. We also present a log message if the
> timestamp jumps more than expected.
Thanks, hopefully we can avoid those
infinite-for-all-practical-purposes loops with this check.
Kristian
> ---
> src/util.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/src/util.c b/src/util.c
> index fa360c2..4ff451a 100644
> --- a/src/util.c
> +++ b/src/util.c
> @@ -46,12 +46,15 @@ weston_spring_update(struct weston_spring *spring,
> uint32_t msec)
> {
> double force, v, current, step;
>
> - /* Avoid entering into an infinite loop */
> - if (msec - spring->timestamp > UINT32_MAX / 2) {
> - weston_log("timestamps going backwards (from %u to %u)\n",
> - spring->timestamp, msec);
> - spring->current = spring->previous = spring->target;
> - return;
> + /* Limit the number of executions of the loop below by ensuring that
> + * the timestamp for last update of the spring is no more than 1s ago.
> + * This handles the case where time moves backwards or forwards in
> + * large jumps.
> + */
> + if (msec - spring->timestamp > 1000) {
> + weston_log("unexpectedly large timestamp jump (from %u to
> %u)\n",
> + spring->timestamp, msec);
> + spring->timestamp = msec - 1000;
> }
>
> step = 0.01;
> --
> 1.7.11.2
>
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