[PATCH] sync: fix corner-case in triggering idle alarms

[Peter Hutterer]

On Wed, Oct 30, 2013 at 04:26:05PM +1000, Peter Hutterer wrote:
> ProcessInputEvent() resets the device idle times. If idle time was higher than
> the lower bracket, this should trigger an event in the idle time wakeup
> handler.
> 
> If processing is slow, the idle time may advance past the lower bracket
> between the reset and the time the BlockHandler is called. In that case, we'd
> never schedule a wakeup to handle the event, causing us to randomly miss
> events.
> 
> Ran tests with a neg transition trigger on 5ms with 200 repeats of the test
> and it succeeded. Anything below that gets a bit tricky to make sure the
> server sees the same idle time as the client usleeps for.
> 
> Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>

Matt, please pull this into 1.14. Thanks.

git cherry-pick -x f36f5a65f639b6524191d888d5bf89e73027156c

Cheers,
   Peter


> ---
>  Xext/sync.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/Xext/sync.c b/Xext/sync.c
> index b2ee92e..53f769d 100644
> --- a/Xext/sync.c
> +++ b/Xext/sync.c
> @@ -2654,7 +2654,16 @@ IdleTimeBlockHandler(pointer pCounter, struct timeval **wt, pointer LastSelectMa
>      IdleTimeQueryValue(counter, &idle);
>      counter->value = idle;      /* push, so CheckTrigger works */
>  
> -    if (less && XSyncValueLessOrEqual(idle, *less)) {
> +    /**
> +     * There's an indefinite amount of time between ProcessInputEvents()
> +     * where the idle time is reset and the time we actually get here. idle
> +     * may be past the lower bracket if we dawdled with the events, so
> +     * check for whether we did reset and bomb out of select immediately.
> +     */
> +    if (less && XSyncValueGreaterThan(idle, *less) &&
> +        LastEventTimeWasReset(priv->deviceid)) {
> +        AdjustWaitForDelay(wt, 0);
> +    } else if (less && XSyncValueLessOrEqual(idle, *less)) {
>          /*
>           * We've been idle for less than the threshold value, and someone
>           * wants to know about that, but now we need to know whether they
> -- 
> 1.8.3.1
> 
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