diff options
Diffstat (limited to 'src/runtime/time.go')
| -rw-r--r-- | src/runtime/time.go | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/src/runtime/time.go b/src/runtime/time.go index b696c837ab..f9335c95f8 100644 --- a/src/runtime/time.go +++ b/src/runtime/time.go @@ -526,6 +526,9 @@ func (t *timer) modify(when, period int64, f func(arg any, seq uintptr, delay in // See comment in type timer above and in timers.adjust below. if when < t.whenHeap { wake = true + // Force timerModified bit out to t.astate before updating t.minWhenModified, + // to synchronize with t.ts.adjust. See comment in adjust. + t.astate.Store(t.state) t.ts.updateMinWhenModified(when) } } @@ -785,6 +788,15 @@ func (ts *timers) adjust(now int64, force bool) { // The wakeTime method implementation reads minWhenModified *before* minWhenHeap, // so that if the minWhenModified is observed to be 0, that means the minWhenHeap that // follows will include the information that was zeroed out of it. + // + // Originally Step 3 locked every timer, which made sure any timer update that was + // already in progress during Steps 1+2 completed and was observed by Step 3. + // All that locking was too expensive, so now we do an atomic load of t.astate to + // decide whether we need to do a full lock. To make sure that we still observe any + // timer update already in progress during Steps 1+2, t.modify sets timerModified + // in t.astate *before* calling t.updateMinWhenModified. That ensures that the + // overwrite in Step 2 cannot lose an update: if it does overwrite an update, Step 3 + // will see the timerModified and do a full lock. ts.minWhenHeap.Store(ts.wakeTime()) ts.minWhenModified.Store(0) |