Add bounded frequency runner

This lib manages runs of a function to have min and max frequencies.
kubernetes · May 25, 2017 · bbb80c2 · bbb80c2
1 parent 3153ca2
commit bbb80c2
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Showing 3 changed files with 573 additions and 2 deletions.
diff --git a/pkg/util/async/BUILD b/pkg/util/async/BUILD
@@ -10,13 +10,23 @@ load(
 
 go_library(
     name = "go_default_library",
-    srcs = ["runner.go"],
+    srcs = [
+        "bounded_frequency_runner.go",
+        "runner.go",
+    ],
     tags = ["automanaged"],
+    deps = [
+        "//vendor/github.com/golang/glog:go_default_library",
+        "//vendor/k8s.io/client-go/util/flowcontrol:go_default_library",
+    ],
 )
 
 go_test(
     name = "go_default_test",
-    srcs = ["runner_test.go"],
+    srcs = [
+        "bounded_frequency_runner_test.go",
+        "runner_test.go",
+    ],
     library = ":go_default_library",
     tags = ["automanaged"],
 )

diff --git a/pkg/util/async/bounded_frequency_runner.go b/pkg/util/async/bounded_frequency_runner.go
@@ -0,0 +1,229 @@
+/*
+Copyright 2017 The Kubernetes 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 async
+
+import (
+	"fmt"
+	"sync"
+	"time"
+
+	"k8s.io/client-go/util/flowcontrol"
+
+	"github.com/golang/glog"
+)
+
+// BoundedFrequencyRunner manages runs of a user-provided function.
+// See NewBoundedFrequencyRunner for examples.
+type BoundedFrequencyRunner struct {
+	name        string        // the name of this instance
+	minInterval time.Duration // the min time between runs, modulo bursts
+	maxInterval time.Duration // the max time between runs
+
+	run chan struct{} // try an async run
+
+	mu      sync.Mutex  // guards runs of fn and all mutations
+	fn      func()      // function to run
+	lastRun time.Time   // time of last run
+	timer   timer       // timer for deferred runs
+	limiter rateLimiter // rate limiter for on-demand runs
+}
+
+// designed so that flowcontrol.RateLimiter satisfies
+type rateLimiter interface {
+	TryAccept() bool
+	Stop()
+}
+
+type nullLimiter struct{}
+
+func (nullLimiter) TryAccept() bool {
+	return true
+}
+
+func (nullLimiter) Stop() {}
+
+var _ rateLimiter = nullLimiter{}
+
+// for testing
+type timer interface {
+	// C returns the timer's selectable channel.
+	C() <-chan time.Time
+
+	// See time.Timer.Reset.
+	Reset(d time.Duration) bool
+
+	// See time.Timer.Stop.
+	Stop() bool
+
+	// See time.Now.
+	Now() time.Time
+
+	// See time.Since.
+	Since(t time.Time) time.Duration
+
+	// See time.Sleep.
+	Sleep(d time.Duration)
+}
+
+// implement our timer in terms of std time.Timer.
+type realTimer struct {
+	*time.Timer
+}
+
+func (rt realTimer) C() <-chan time.Time {
+	return rt.Timer.C
+}
+
+func (rt realTimer) Now() time.Time {
+	return time.Now()
+}
+
+func (rt realTimer) Since(t time.Time) time.Duration {
+	return time.Since(t)
+}
+
+func (rt realTimer) Sleep(d time.Duration) {
+	time.Sleep(d)
+}
+
+var _ timer = realTimer{}
+
+// NewBoundedFrequencyRunner creates a new BoundedFrequencyRunner instance,
+// which will manage runs of the specified function.
+//
+// All runs will be async to the caller of BoundedFrequencyRunner.Run, but
+// multiple runs are serialized. If the function needs to hold locks, it must
+// take them internally.
+//
+// Runs of the funtion will have at least minInterval between them (from
+// completion to next start), except that up to bursts may be allowed.  Burst
+// runs are "accumulated" over time, one per minInterval up to burstRuns total.
+// This can be used, for example, to mitigate the impact of expensive operations
+// being called in response to user-initiated operations. Run requests that
+// would violate the minInterval are coallesced and run at the next opportunity.
+//
+// The function will be run at least once per maxInterval. For example, this can
+// force periodic refreshes of state in the absence of anyone calling Run.
+//
+// Examples:
+//
+// NewBoundedFrequencyRunner("name", fn, time.Second, 5*time.Second, 1)
+// - fn will have at least 1 second between runs
+// - fn will have no more than 5 seconds between runs
+//
+// NewBoundedFrequencyRunner("name", fn, 3*time.Second, 10*time.Second, 3)
+// - fn will have at least 3 seconds between runs, with up to 3 burst runs
+// - fn will have no more than 10 seconds between runs
+//
+// The maxInterval must be greater than or equal to the minInterval,  If the
+// caller passes a maxInterval less than minInterval, this function will panic.
+func NewBoundedFrequencyRunner(name string, fn func(), minInterval, maxInterval time.Duration, burstRuns int) *BoundedFrequencyRunner {
+	timer := realTimer{Timer: time.NewTimer(0)} // will tick immediately
+	<-timer.C()                                 // consume the first tick
+	return construct(name, fn, minInterval, maxInterval, burstRuns, timer)
+}
+
+// Make an instance with dependencies injected.
+func construct(name string, fn func(), minInterval, maxInterval time.Duration, burstRuns int, timer timer) *BoundedFrequencyRunner {
+	if maxInterval < minInterval {
+		panic(fmt.Sprintf("%s: maxInterval (%v) must be >= minInterval (%v)", name, minInterval, maxInterval))
+	}
+	if timer == nil {
+		panic(fmt.Sprintf("%s: timer must be non-nil", name))
+	}
+
+	bfr := &BoundedFrequencyRunner{
+		name:        name,
+		fn:          fn,
+		minInterval: minInterval,
+		maxInterval: maxInterval,
+		run:         make(chan struct{}, 16),
+		timer:       timer,
+	}
+	if minInterval == 0 {
+		bfr.limiter = nullLimiter{}
+	} else {
+		// allow burst updates in short succession
+		qps := float32(time.Second) / float32(minInterval)
+		bfr.limiter = flowcontrol.NewTokenBucketRateLimiterWithClock(qps, burstRuns, timer)
+	}
+	return bfr
+}
+
+// Loop handles the periodic timer and run requests.  This is expected to be
+// called as a goroutine.
+func (bfr *BoundedFrequencyRunner) Loop(stop <-chan struct{}) {
+	glog.V(3).Infof("%s Loop running", bfr.name)
+	bfr.timer.Reset(bfr.maxInterval)
+	for {
+		select {
+		case <-stop:
+			bfr.stop()
+			glog.V(3).Infof("%s Loop stopping", bfr.name)
+			return
+		case <-bfr.timer.C():
+			bfr.tryRun()
+		case <-bfr.run:
+			bfr.tryRun()
+		}
+	}
+}
+
+// Run the function as soon as possible.  If this is called while Loop is not
+// running, the call may be deferred indefinitely.
+func (bfr *BoundedFrequencyRunner) Run() {
+	bfr.run <- struct{}{}
+}
+
+// assumes the lock is not held
+func (bfr *BoundedFrequencyRunner) stop() {
+	bfr.mu.Lock()
+	defer bfr.mu.Unlock()
+	bfr.limiter.Stop()
+	bfr.timer.Stop()
+}
+
+// assumes the lock is not held
+func (bfr *BoundedFrequencyRunner) tryRun() {
+	bfr.mu.Lock()
+	defer bfr.mu.Unlock()
+
+	if bfr.limiter.TryAccept() {
+		// We're allowed to run the function right now.
+		bfr.fn()
+		bfr.lastRun = bfr.timer.Now()
+		bfr.timer.Stop()
+		bfr.timer.Reset(bfr.maxInterval)
+		glog.V(3).Infof("%s: ran, next possible in %v, periodic in %v", bfr.name, bfr.minInterval, bfr.maxInterval)
+		return
+	}
+
+	// It can't run right now, figure out when it can run next.
+
+	elapsed := bfr.timer.Since(bfr.lastRun)    // how long since last run
+	nextPossible := bfr.minInterval - elapsed  // time to next possible run
+	nextScheduled := bfr.maxInterval - elapsed // time to next periodic run
+	glog.V(4).Infof("%s: %v since last run, possible in %v, scheduled in %v", bfr.name, elapsed, nextPossible, nextScheduled)
+
+	if nextPossible < nextScheduled {
+		// Set the timer for ASAP, but don't drain here.  Assuming Loop is running,
+		// it might get a delivery in the mean time, but that is OK.
+		bfr.timer.Stop()
+		bfr.timer.Reset(nextPossible)
+		glog.V(3).Infof("%s: throttled, scheduling run in %v", bfr.name, nextPossible)
+	}
+}