[LEAPSECS] Coding this week, and a trick for timeouts over leap seconds.

[Gerard Ashton]

Perhaps one of the systems has, or will in the future have, code which 
smears the leap
second out over a day, or an hour. In that case the period over which 
the special
provision is applied is insufficient, and knowledge of the month and day 
would
be required to decide if a leap second is possible that day.

Gerard Ashton

On 10/1/2011 5:16 AM, Paul Sheer wrote:

> I am busy implementing some heartbeat monitoring code between two

> machines. The spec calls for a 1 second recovery.

>

> Basically if I get no heartbeats for 1 full second then I should

> consider the peer system to have failed.

>

> To cope with the leap-second scenario, one solution is to use a

> timeout of 1 second longer than usual if the current time is close

> to the turnover of the day. You can do this easily by checking

>

>     time(NULL) % 86400

>

> and if we are at the turnover of the day use a 2 second timeout

> instead of a 1 second timeout.

>

> Now this seems like a nice and easy way of fixing old code. Here

> is an example:

>

>

> void process_event(Event e)

> {

>     long long now = gettimeofday_in_millisecs();

>     if (now>  last_recv_time + 1000) {

>        peer_has_failed();

>     } else if (e == EVENT_HEARTBEAT) {

>        last_recv_time = now;

>     }

> }

>

>

> Becomes:

>

>

> int near_turnover_of_day(long long t)

> {

> #define FUDGE 2

>     if ((t + FUDGE) % 86400<= FUDGE * 2)

>        return 1;

>     return 0;

> }

>

> void process_heartbeat(Event e)

> {

>     long long now = gettimeofday_in_millisecs();

>     if (now>  last_recv_time + 1000 +

>               1000 * near_turnover_of_day(now / 1000)) {

>        peer_has_failed();

>     } else if (e == EVENT_HEARTBEAT) {

>        last_recv_time = now;

>     }

> }

>

>

> Comments?

>

> (This example is off the top of my head so please excuse any errors.)

>

> -paul

>

>

>

>

>

>

>

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