Small refactor of gc/scheduler to remove import of metadata

Replace metadata.GCStats with an interface for exposing elapsed time

Signed-off-by: Daniel Nephin <dnephin@gmail.com>

gc/gc.go

@@ -8,6 +8,7 @@ package gc
 import (
 	"context"
 	"sync"
+	"time"
 )
 
 // ResourceType represents type of resource at a node
@@ -21,6 +22,11 @@ type Node struct {
 	Key       string
 }
 
+// Stats about a garbage collection run
+type Stats interface {
+	Elapsed() time.Duration
+}
+
 // Tricolor implements basic, single-thread tri-color GC. Given the roots, the
 // complete set and a refs function, this function returns a map of all
 // reachable objects.

gc/scheduler/scheduler.go

@@ -2,14 +2,14 @@ package scheduler
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"sync"
 	"time"
 
+	"github.com/containerd/containerd/gc"
 	"github.com/containerd/containerd/log"
-	"github.com/containerd/containerd/metadata"
 	"github.com/containerd/containerd/plugin"
+	"github.com/pkg/errors"
 )
 
 // config configures the garbage collection policies.
@@ -95,7 +95,12 @@ func init() {
 				return nil, err
 			}
 
-			m := newScheduler(md.(*metadata.DB), ic.Config.(*config))
+			mdCollector, ok := md.(collector)
+			if !ok {
+				return nil, errors.Errorf("%s %T must implement collector", plugin.MetadataPlugin, md)
+			}
+
+			m := newScheduler(mdCollector, ic.Config.(*config))
 
 			ic.Meta.Exports = map[string]string{
 				"PauseThreshold":    fmt.Sprint(m.pauseThreshold),
@@ -119,7 +124,7 @@ type mutationEvent struct {
 
 type collector interface {
 	RegisterMutationCallback(func(bool))
-	GarbageCollect(context.Context) (metadata.GCStats, error)
+	GarbageCollect(context.Context) (gc.Stats, error)
 }
 
 type gcScheduler struct {
@@ -128,7 +133,7 @@ type gcScheduler struct {
 	eventC chan mutationEvent
 
 	waiterL sync.Mutex
-	waiters []chan metadata.GCStats
+	waiters []chan gc.Stats
 
 	pauseThreshold    float64
 	deletionThreshold int
@@ -171,12 +176,12 @@ func newScheduler(c collector, cfg *config) *gcScheduler {
 	return s
 }
 
-func (s *gcScheduler) ScheduleAndWait(ctx context.Context) (metadata.GCStats, error) {
+func (s *gcScheduler) ScheduleAndWait(ctx context.Context) (gc.Stats, error) {
 	return s.wait(ctx, true)
 }
 
-func (s *gcScheduler) wait(ctx context.Context, trigger bool) (metadata.GCStats, error) {
-	wc := make(chan metadata.GCStats, 1)
+func (s *gcScheduler) wait(ctx context.Context, trigger bool) (gc.Stats, error) {
+	wc := make(chan gc.Stats, 1)
 	s.waiterL.Lock()
 	s.waiters = append(s.waiters, wc)
 	s.waiterL.Unlock()
@@ -190,15 +195,15 @@ func (s *gcScheduler) wait(ctx context.Context, trigger bool) (metadata.GCStats,
 		}()
 	}
 
-	var gcStats metadata.GCStats
+	var gcStats gc.Stats
 	select {
 	case stats, ok := <-wc:
 		if !ok {
-			return metadata.GCStats{}, errors.New("gc failed")
+			return gcStats, errors.New("gc failed")
 		}
 		gcStats = stats
 	case <-ctx.Done():
-		return metadata.GCStats{}, ctx.Err()
+		return gcStats, ctx.Err()
 	}
 
 	return gcStats, nil
@@ -301,9 +306,9 @@ func (s *gcScheduler) run(ctx context.Context) {
 			continue
 		}
 
-		log.G(ctx).WithField("d", stats.MetaD).Debug("garbage collected")
+		log.G(ctx).WithField("d", stats.Elapsed()).Debug("garbage collected")
 
-		gcTime += stats.MetaD
+		gcTime += stats.Elapsed()
 		collections++
 		triggered = false
 		deletions = 0

gc/scheduler/scheduler_test.go

@@ -6,11 +6,11 @@ import (
 	"testing"
 	"time"
 
-	"github.com/containerd/containerd/metadata"
+	"github.com/containerd/containerd/gc"
+	"github.com/stretchr/testify/require"
 )
 
 func TestPauseThreshold(t *testing.T) {
-
 	cfg := &config{
 		// With 100μs, gc should run about every 5ms
 		PauseThreshold: 0.02,
@@ -99,7 +99,7 @@ func TestTrigger(t *testing.T) {
 		}
 		ctx, cancel = context.WithCancel(context.Background())
 		scheduler   = newScheduler(tc, cfg)
-		stats       metadata.GCStats
+		stats       gc.Stats
 		err         error
 	)
 
@@ -123,9 +123,7 @@ func TestTrigger(t *testing.T) {
 		t.Fatalf("GC failed: %#v", err)
 	}
 
-	if stats.MetaD != tc.d {
-		t.Fatalf("unexpected gc duration: %s, expected %d", stats.MetaD, tc.d)
-	}
+	require.Equal(t, tc.d, stats.Elapsed())
 
 	if c := tc.runCount(); c != 1 {
 		t.Fatalf("unexpected gc run count %d, expected 1", c)
@@ -180,11 +178,18 @@ func (tc *testCollector) RegisterMutationCallback(f func(bool)) {
 	tc.callbacks = append(tc.callbacks, f)
 }
 
-func (tc *testCollector) GarbageCollect(context.Context) (metadata.GCStats, error) {
+func (tc *testCollector) GarbageCollect(context.Context) (gc.Stats, error) {
 	tc.m.Lock()
 	tc.gc++
 	tc.m.Unlock()
-	return metadata.GCStats{
-		MetaD: tc.d,
-	}, nil
+	return gcStats{elapsed: tc.d}, nil
+}
+
+type gcStats struct {
+	elapsed time.Duration
+}
+
+// Elapsed returns the duration which elapsed during a collection
+func (s gcStats) Elapsed() time.Duration {
+	return s.elapsed
 }

metadata/db.go

@@ -204,7 +204,7 @@ func (m *DB) Update(fn func(*bolt.Tx) error) error {
 // RegisterMutationCallback registers a function to be called after a metadata
 // mutations has been performed.
 //
-// The callback function in an argument for whether a deletion has occurred
+// The callback function is an argument for whether a deletion has occurred
 // since the last garbage collection.
 func (m *DB) RegisterMutationCallback(fn func(bool)) {
 	m.dirtyL.Lock()
@@ -219,15 +219,20 @@ type GCStats struct {
 	SnapshotD map[string]time.Duration
 }
 
+// Elapsed returns the duration which elapsed during a collection
+func (s GCStats) Elapsed() time.Duration {
+	return s.MetaD
+}
+
 // GarbageCollect starts garbage collection
-func (m *DB) GarbageCollect(ctx context.Context) (stats GCStats, err error) {
+func (m *DB) GarbageCollect(ctx context.Context) (gc.Stats, error) {
 	m.wlock.Lock()
 	t1 := time.Now()
 
 	marked, err := m.getMarked(ctx)
 	if err != nil {
 		m.wlock.Unlock()
-		return GCStats{}, err
+		return nil, err
 	}
 
 	m.dirtyL.Lock()
@@ -259,9 +264,10 @@ func (m *DB) GarbageCollect(ctx context.Context) (stats GCStats, err error) {
 	}); err != nil {
 		m.dirtyL.Unlock()
 		m.wlock.Unlock()
-		return GCStats{}, err
+		return nil, err
 	}
 
+	var stats GCStats
 	var wg sync.WaitGroup
 
 	if len(m.dirtySS) > 0 {
@@ -303,7 +309,7 @@ func (m *DB) GarbageCollect(ctx context.Context) (stats GCStats, err error) {
 
 	wg.Wait()
 
-	return
+	return stats, err
 }
 
 func (m *DB) getMarked(ctx context.Context) (map[gc.Node]struct{}, error) {

services/images/service.go

@@ -8,6 +8,7 @@ import (
 	imagesapi "github.com/containerd/containerd/api/services/images/v1"
 	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/events"
+	"github.com/containerd/containerd/gc"
 	"github.com/containerd/containerd/images"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/metadata"
@@ -43,7 +44,7 @@ func init() {
 }
 
 type gcScheduler interface {
-	ScheduleAndWait(gocontext.Context) (metadata.GCStats, error)
+	ScheduleAndWait(gocontext.Context) (gc.Stats, error)
 }
 
 type service struct {