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Do not advance decay epoch when time goes backwards.

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Instead, move the epoch backward in time.  Additionally, add
nstime_monotonic() and use it in debug builds to assert that time only
goes backward if nstime_update() is using a non-monotonic time source.
This commit is contained in:
Jason Evans 2016-10-10 22:15:10 -07:00
parent ee0c74b77a
commit 5f11fb7d43
6 changed files with 63 additions and 6 deletions
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21
src/arena.c
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@ -693,10 +693,23 @@ arena_maybe_purge_decay(tsdn_t *tsdn, arena_t *arena)
return;
}
nstime_copy(&time, &arena->decay.epoch);
if (unlikely(nstime_update(&time))) {
/* Time went backwards. Force an epoch advance. */
nstime_copy(&time, &arena->decay.deadline);
nstime_init(&time, 0);
nstime_update(&time);
if (unlikely(!nstime_monotonic() && nstime_compare(&arena->decay.epoch,
&time) > 0)) {
/*
* Time went backwards. Move the epoch back in time, with the
* expectation that time typically flows forward for long enough
* periods of time that epochs complete. Unfortunately,
* this strategy is susceptible to clock jitter triggering
* premature epoch advances, but clock jitter estimation and
* compensation isn't feasible here because calls into this code
* are event-driven.
*/
nstime_copy(&arena->decay.epoch, &time);
} else {
/* Verify that time does not go backwards. */
assert(nstime_compare(&arena->decay.epoch, &time) <= 0);
}
if (arena_decay_deadline_reached(arena, &time))