Simplify proxy scheduler

The proxy scheduler implemented its own timer state machine. It's
simpler and more efficient to leverage the Go runtime's timer heap by
using time.AfterFunc.

This commit adds a time.Timer to each scheduler entry, and starts and
stops those timers as necessary. Then the mainloop goroutine and its
associated logic are not needed.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

registry/proxy/scheduler/scheduler.go

@@ -3,13 +3,14 @@ package scheduler
 import (
 	"encoding/json"
 	"fmt"
+	"sync"
 	"time"
 
 	"github.com/docker/distribution/context"
 	"github.com/docker/distribution/registry/storage/driver"
 )
 
-// onTTLExpiryFunc is called when a repositories' TTL expires
+// onTTLExpiryFunc is called when a repository's TTL expires
 type expiryFunc func(string) error
 
 const (
@@ -23,14 +24,14 @@ type schedulerEntry struct {
 	Key       string    `json:"Key"`
 	Expiry    time.Time `json:"ExpiryData"`
 	EntryType int       `json:"EntryType"`
+
+	timer *time.Timer
 }
 
 // New returns a new instance of the scheduler
 func New(ctx context.Context, driver driver.StorageDriver, path string) *TTLExpirationScheduler {
 	return &TTLExpirationScheduler{
-		entries:         make(map[string]schedulerEntry),
-		addChan:         make(chan schedulerEntry),
-		stopChan:        make(chan bool),
+		entries:         make(map[string]*schedulerEntry),
 		driver:          driver,
 		pathToStateFile: path,
 		ctx:             ctx,
@@ -41,9 +42,9 @@ func New(ctx context.Context, driver driver.StorageDriver, path string) *TTLExpi
 // TTLExpirationScheduler is a scheduler used to perform actions
 // when TTLs expire
 type TTLExpirationScheduler struct {
-	entries  map[string]schedulerEntry
-	addChan  chan schedulerEntry
-	stopChan chan bool
+	sync.Mutex
+
+	entries map[string]*schedulerEntry
 
 	driver          driver.StorageDriver
 	ctx             context.Context
@@ -55,24 +56,27 @@ type TTLExpirationScheduler struct {
 	onManifestExpire expiryFunc
 }
 
-// addChan allows more TTLs to be pushed to the scheduler
-type addChan chan schedulerEntry
-
-// stopChan allows the scheduler to be stopped - used for testing.
-type stopChan chan bool
-
 // OnBlobExpire is called when a scheduled blob's TTL expires
 func (ttles *TTLExpirationScheduler) OnBlobExpire(f expiryFunc) {
+	ttles.Lock()
+	defer ttles.Unlock()
+
 	ttles.onBlobExpire = f
 }
 
 // OnManifestExpire is called when a scheduled manifest's TTL expires
 func (ttles *TTLExpirationScheduler) OnManifestExpire(f expiryFunc) {
+	ttles.Lock()
+	defer ttles.Unlock()
+
 	ttles.onManifestExpire = f
 }
 
 // AddBlob schedules a blob cleanup after ttl expires
 func (ttles *TTLExpirationScheduler) AddBlob(dgst string, ttl time.Duration) error {
+	ttles.Lock()
+	defer ttles.Unlock()
+
 	if ttles.stopped {
 		return fmt.Errorf("scheduler not started")
 	}
@@ -82,6 +86,9 @@ func (ttles *TTLExpirationScheduler) AddBlob(dgst string, ttl time.Duration) err
 
 // AddManifest schedules a manifest cleanup after ttl expires
 func (ttles *TTLExpirationScheduler) AddManifest(repoName string, ttl time.Duration) error {
+	ttles.Lock()
+	defer ttles.Unlock()
+
 	if ttles.stopped {
 		return fmt.Errorf("scheduler not started")
 	}
@@ -92,23 +99,9 @@ func (ttles *TTLExpirationScheduler) AddManifest(repoName string, ttl time.Durat
 
 // Start starts the scheduler
 func (ttles *TTLExpirationScheduler) Start() error {
-	return ttles.start()
-}
+	ttles.Lock()
+	defer ttles.Unlock()
 
-func (ttles *TTLExpirationScheduler) add(key string, ttl time.Duration, eType int) {
-	entry := schedulerEntry{
-		Key:       key,
-		Expiry:    time.Now().Add(ttl),
-		EntryType: eType,
-	}
-	ttles.addChan <- entry
-}
-
-func (ttles *TTLExpirationScheduler) stop() {
-	ttles.stopChan <- true
-}
-
-func (ttles *TTLExpirationScheduler) start() error {
 	err := ttles.readState()
 	if err != nil {
 		return err
@@ -120,97 +113,75 @@ func (ttles *TTLExpirationScheduler) start() error {
 
 	context.GetLogger(ttles.ctx).Infof("Starting cached object TTL expiration scheduler...")
 	ttles.stopped = false
-	go ttles.mainloop()
+
+	// Start timer for each deserialized entry
+	for _, entry := range ttles.entries {
+		entry.timer = ttles.startTimer(entry, entry.Expiry.Sub(time.Now()))
+	}
 
 	return nil
 }
 
-// mainloop uses a select statement to listen for events.  Most of its time
-// is spent in waiting on a TTL to expire but can be interrupted when TTLs
-// are added.
-func (ttles *TTLExpirationScheduler) mainloop() {
-	for {
-		if ttles.stopped {
-			return
-		}
+func (ttles *TTLExpirationScheduler) add(key string, ttl time.Duration, eType int) {
+	entry := &schedulerEntry{
+		Key:       key,
+		Expiry:    time.Now().Add(ttl),
+		EntryType: eType,
+	}
+	context.GetLogger(ttles.ctx).Infof("Adding new scheduler entry for %s with ttl=%s", entry.Key, entry.Expiry.Sub(time.Now()))
+	if oldEntry, present := ttles.entries[key]; present && oldEntry.timer != nil {
+		oldEntry.timer.Stop()
+	}
+	ttles.entries[key] = entry
+	entry.timer = ttles.startTimer(entry, ttl)
 
-		nextEntry, ttl := nextExpiringEntry(ttles.entries)
-		if len(ttles.entries) == 0 {
-			context.GetLogger(ttles.ctx).Infof("scheduler mainloop(): Nothing to do, sleeping...")
-		} else {
-			context.GetLogger(ttles.ctx).Infof("scheduler mainloop(): Sleeping for %s until cleanup of %s", ttl, nextEntry.Key)
-		}
-
-		select {
-		case <-time.After(ttl):
-			var f expiryFunc
-
-			switch nextEntry.EntryType {
-			case entryTypeBlob:
-				f = ttles.onBlobExpire
-			case entryTypeManifest:
-				f = ttles.onManifestExpire
-			default:
-				f = func(repoName string) error {
-					return fmt.Errorf("Unexpected scheduler entry type")
-				}
-			}
-
-			if err := f(nextEntry.Key); err != nil {
-				context.GetLogger(ttles.ctx).Errorf("Scheduler error returned from OnExpire(%s): %s", nextEntry.Key, err)
-			}
-
-			delete(ttles.entries, nextEntry.Key)
-			if err := ttles.writeState(); err != nil {
-				context.GetLogger(ttles.ctx).Errorf("Error writing scheduler state: %s", err)
-			}
-		case entry := <-ttles.addChan:
-			context.GetLogger(ttles.ctx).Infof("Adding new scheduler entry for %s with ttl=%s", entry.Key, entry.Expiry.Sub(time.Now()))
-			ttles.entries[entry.Key] = entry
-			if err := ttles.writeState(); err != nil {
-				context.GetLogger(ttles.ctx).Errorf("Error writing scheduler state: %s", err)
-			}
-			break
-
-		case <-ttles.stopChan:
-			if err := ttles.writeState(); err != nil {
-				context.GetLogger(ttles.ctx).Errorf("Error writing scheduler state: %s", err)
-			}
-			ttles.stopped = true
-		}
+	if err := ttles.writeState(); err != nil {
+		context.GetLogger(ttles.ctx).Errorf("Error writing scheduler state: %s", err)
 	}
 }
 
-func nextExpiringEntry(entries map[string]schedulerEntry) (*schedulerEntry, time.Duration) {
-	if len(entries) == 0 {
-		return nil, 24 * time.Hour
-	}
+func (ttles *TTLExpirationScheduler) startTimer(entry *schedulerEntry, ttl time.Duration) *time.Timer {
+	return time.AfterFunc(ttl, func() {
+		ttles.Lock()
+		defer ttles.Unlock()
 
-	// todo:(richardscothern) this is a primitive o(n) algorithm
-	// but n will never be *that* big and it's all in memory.  Investigate
-	// time.AfterFunc for heap based expiries
+		var f expiryFunc
 
-	first := true
-	var nextEntry schedulerEntry
-	for _, entry := range entries {
-		if first {
-			nextEntry = entry
-			first = false
-			continue
+		switch entry.EntryType {
+		case entryTypeBlob:
+			f = ttles.onBlobExpire
+		case entryTypeManifest:
+			f = ttles.onManifestExpire
+		default:
+			f = func(repoName string) error {
+				return fmt.Errorf("Unexpected scheduler entry type")
+			}
 		}
-		if entry.Expiry.Before(nextEntry.Expiry) {
-			nextEntry = entry
+
+		if err := f(entry.Key); err != nil {
+			context.GetLogger(ttles.ctx).Errorf("Scheduler error returned from OnExpire(%s): %s", entry.Key, err)
 		}
+
+		delete(ttles.entries, entry.Key)
+		if err := ttles.writeState(); err != nil {
+			context.GetLogger(ttles.ctx).Errorf("Error writing scheduler state: %s", err)
+		}
+	})
+}
+
+// Stop stops the scheduler.
+func (ttles *TTLExpirationScheduler) Stop() {
+	ttles.Lock()
+	defer ttles.Unlock()
+
+	if err := ttles.writeState(); err != nil {
+		context.GetLogger(ttles.ctx).Errorf("Error writing scheduler state: %s", err)
 	}
 
-	// Dates may be from the past if the scheduler has
-	// been restarted, set their ttl to 0
-	if nextEntry.Expiry.Before(time.Now()) {
-		nextEntry.Expiry = time.Now()
-		return &nextEntry, 0
+	for _, entry := range ttles.entries {
+		entry.timer.Stop()
 	}
-
-	return &nextEntry, nextEntry.Expiry.Sub(time.Now())
+	ttles.stopped = true
 }
 
 func (ttles *TTLExpirationScheduler) writeState() error {

registry/proxy/scheduler/scheduler_test.go

@@ -2,7 +2,6 @@ package scheduler
 
 import (
 	"encoding/json"
-	"fmt"
 	"testing"
 	"time"
 
@@ -27,13 +26,13 @@ func TestSchedule(t *testing.T) {
 		if !ok {
 			t.Fatalf("Trying to remove nonexistant repo: %s", repoName)
 		}
-		fmt.Println("removing", repoName)
+		t.Log("removing", repoName)
 		delete(remainingRepos, repoName)
 
 		return nil
 	}
 	s.onBlobExpire = deleteFunc
-	err := s.start()
+	err := s.Start()
 	if err != nil {
 		t.Fatalf("Error starting ttlExpirationScheduler: %s", err)
 	}
@@ -97,7 +96,7 @@ func TestRestoreOld(t *testing.T) {
 	}
 	s := New(context.Background(), fs, "/ttl")
 	s.onBlobExpire = deleteFunc
-	err = s.start()
+	err = s.Start()
 	if err != nil {
 		t.Fatalf("Error starting ttlExpirationScheduler: %s", err)
 	}
@@ -124,7 +123,7 @@ func TestStopRestore(t *testing.T) {
 	s := New(context.Background(), fs, pathToStateFile)
 	s.onBlobExpire = deleteFunc
 
-	err := s.start()
+	err := s.Start()
 	if err != nil {
 		t.Fatalf(err.Error())
 	}
@@ -133,13 +132,13 @@ func TestStopRestore(t *testing.T) {
 
 	// Start and stop before all operations complete
 	// state will be written to fs
-	s.stop()
+	s.Stop()
 	time.Sleep(10 * time.Millisecond)
 
 	// v2 will restore state from fs
 	s2 := New(context.Background(), fs, pathToStateFile)
 	s2.onBlobExpire = deleteFunc
-	err = s2.start()
+	err = s2.Start()
 	if err != nil {
 		t.Fatalf("Error starting v2: %s", err.Error())
 	}
@@ -153,12 +152,11 @@ func TestStopRestore(t *testing.T) {
 
 func TestDoubleStart(t *testing.T) {
 	s := New(context.Background(), inmemory.New(), "/ttl")
-	err := s.start()
+	err := s.Start()
 	if err != nil {
 		t.Fatalf("Unable to start scheduler")
 	}
-	fmt.Printf("%#v", s)
-	err = s.start()
+	err = s.Start()
 	if err == nil {
 		t.Fatalf("Scheduler started twice without error")
 	}