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fn: hot container timer improvements (#751)

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* fn: hot container timer improvements

With this change, now we are allocating the timers
when the container starts and managing them via
stop/clear as needed, which should not only be more
efficient, but also easier to follow.

For example, previously, if eject time out was
set to 10 secs, this could have delayed idle timeout
up to 10 secs as well. It is also not necessary to do
any math for elapsed time.

Now consumers avoid any requeuing when startDequeuer() is cancelled.
This was triggering additional dequeue/requeue causing
containers to wake up spuriously. Also in startDequeuer(),
we no longer remove the item from the actual queue and
leave this to acquire/eject, which side steps issues related
with item landing in the channel, not consumed, etc.
This commit is contained in:
Tolga Ceylan
2018-02-12 14:12:03 -08:00
committed by GitHub
parent ffcda9b823
commit c848fc6181
4 changed files with 191 additions and 241 deletions
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23
api/agent/slots.go
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@@ -70,25 +70,15 @@ func NewSlotQueue(key string) *slotQueue {
return obj
}
func (a *slotToken) acquireSlot() bool {
// let's get the lock
if !atomic.CompareAndSwapUint32(&a.isBusy, 0, 1) {
return false
}
// now we have the lock, push the trigger
close(a.trigger)
return true
}
func (a *slotQueue) ejectSlot(ctx context.Context, s *slotToken) bool {
func (a *slotQueue) acquireSlot(s *slotToken) bool {
// let's get the lock
if !atomic.CompareAndSwapUint32(&s.isBusy, 0, 1) {
return false
}
a.cond.L.Lock()
for i := 0; i < len(a.slots); i++ {
// common case: acquired slots are usually at the end
for i := len(a.slots) - 1; i >= 0; i-- {
if a.slots[i].id == s.id {
a.slots = append(a.slots[:i], a.slots[i+1:]...)
break
@@ -96,7 +86,6 @@ func (a *slotQueue) ejectSlot(ctx context.Context, s *slotToken) bool {
}
a.cond.L.Unlock()
s.slot.Close(ctx)
// now we have the lock, push the trigger
close(s.trigger)
return true
@@ -131,19 +120,13 @@ func (a *slotQueue) startDequeuer(ctx context.Context) chan *slotToken {
return
}
// pop
item := a.slots[len(a.slots)-1]
a.slots = a.slots[:len(a.slots)-1]
a.cond.L.Unlock()
select {
case output <- item: // good case (dequeued)
case <-item.trigger: // ejected (eject handles cleanup)
case <-ctx.Done(): // time out or cancel from caller
// consume slot, we let the hot container queue the slot again
if item.acquireSlot() {
item.slot.Close(ctx)
}
}
}
}()