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strategy.go
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strategy.go
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// Copyright 2018 Istio Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package runtime
import (
"sync"
"time"
)
const (
// Maximum wait time before deciding to publish the events.
defaultMaxWaitDuration = time.Second
// Minimum time distance between two events for deciding on the quiesce point. If the time delay
// between two events is larger than this, then we can deduce that we hit a quiesce point.
defaultQuiesceDuration = time.Second
// The frequency for firing the timer events.
defaultTimerFrequency = 500 * time.Millisecond
)
// publishingStrategy is a heuristic model for deciding when to publish snapshots. It tries to detect
// quiesce points for events with a total bounded wait time.
type publishingStrategy struct {
maxWaitDuration time.Duration
quiesceDuration time.Duration
timerFrequency time.Duration
// stateLock protects the internal state of the publishing strategy.
stateLock sync.Mutex
// publish channel is used to trigger the publication of snapshots.
publish chan struct{}
// the time of first event that is received.
firstEvent time.Time
// the time of the latest event that is received.
latestEvent time.Time
// timer that is used for periodically checking for the quiesce point.
timer *time.Timer
// nowFn is a testing hook for overriding time.Now()
nowFn func() time.Time
// afterFuncFn is a testing hook for overriding time.AfterFunc()
afterFuncFn func(time.Duration, func()) *time.Timer
}
func newPublishingStrategyWithDefaults() *publishingStrategy {
return newPublishingStrategy(defaultMaxWaitDuration, defaultQuiesceDuration, defaultTimerFrequency)
}
func newPublishingStrategy(
maxWaitDuration time.Duration,
quiesceDuration time.Duration,
timerFrequency time.Duration) *publishingStrategy {
return &publishingStrategy{
maxWaitDuration: maxWaitDuration,
quiesceDuration: quiesceDuration,
timerFrequency: timerFrequency,
publish: make(chan struct{}, 1),
nowFn: time.Now,
afterFuncFn: time.AfterFunc,
}
}
func (s *publishingStrategy) onChange() {
s.stateLock.Lock()
recordStrategyOnChange()
defer s.stateLock.Unlock()
// Capture the latest event time.
s.latestEvent = s.nowFn()
if s.timer == nil {
// If this is the first event after a quiesce, start a timer to periodically check event
// frequency and fire the publish event.
s.firstEvent = s.latestEvent
s.timer = s.afterFuncFn(s.timerFrequency, s.onTimer)
}
}
func (s *publishingStrategy) onTimer() {
s.stateLock.Lock()
defer s.stateLock.Unlock()
now := s.nowFn()
// If there has been a long time since the first event, or if there was a quiesce since last event,
// then fire publish to create new snapshots.
// Otherwise, reset the timer and get a call again.
maxTimeReached := now.After(s.firstEvent.Add(s.maxWaitDuration))
quiesceTimeReached := now.After(s.latestEvent.Add(s.quiesceDuration))
var published bool
if maxTimeReached || quiesceTimeReached {
// Try to send to the channel
select {
case s.publish <- struct{}{}:
published = true
default:
// If the calling code is not draining the publish channel, then we can potentially cause
// a deadlock here. Avoid the deadlock by going through the timer loop again.
scope.Warnf("Unable to publish to the channel, resetting the timer again to avoid deadlock")
}
}
recordOnTimer(maxTimeReached, quiesceTimeReached, !published)
if published {
s.timer = nil
} else {
s.timer.Reset(s.timerFrequency)
}
}
func (s *publishingStrategy) reset() {
s.stateLock.Lock()
defer s.stateLock.Unlock()
if s.timer != nil {
s.timer.Stop()
s.timer = nil
}
}