Trigger pull check on remote index updates (fixes #1765)

Without this, when an index update comes in we only do a new pull if the
remote `localVersion` was increased. But it may not be, because the
index is sent alphabetically and the file with the highest local version
may come first. In that case we'll never do a new pull when the rest of
the index comes in, and we'll be stuck in idle but with lots of out of
sync data.

internal/model/model.go

@@ -50,6 +50,7 @@ type service interface {
 	Jobs() ([]string, []string) // In progress, Queued
 	BringToFront(string)
 	DelayScan(d time.Duration)
+	IndexUpdated() // Remote index was updated notification
 
 	setState(state folderState)
 	setError(err error)
@@ -469,8 +470,15 @@ func (m *Model) Index(deviceID protocol.DeviceID, folder string, fs []protocol.F
 
 	m.fmut.RLock()
 	files, ok := m.folderFiles[folder]
+	runner := m.folderRunners[folder]
 	m.fmut.RUnlock()
 
+	if runner != nil {
+		// Runner may legitimately not be set if this is the "cleanup" Index
+		// message at startup.
+		defer runner.IndexUpdated()
+	}
+
 	if !ok {
 		l.Fatalf("Index for nonexistant folder %q", folder)
 	}
@@ -521,7 +529,8 @@ func (m *Model) IndexUpdate(deviceID protocol.DeviceID, folder string, fs []prot
 	}
 
 	m.fmut.RLock()
-	files, ok := m.folderFiles[folder]
+	files := m.folderFiles[folder]
+	runner, ok := m.folderRunners[folder]
 	m.fmut.RUnlock()
 
 	if !ok {
@@ -554,6 +563,8 @@ func (m *Model) IndexUpdate(deviceID protocol.DeviceID, folder string, fs []prot
 		"items":   len(fs),
 		"version": files.LocalVersion(deviceID),
 	})
+
+	runner.IndexUpdated()
 }
 
 func (m *Model) folderSharedWith(folder string, deviceID protocol.DeviceID) bool {

internal/model/rofolder.go

@@ -104,6 +104,9 @@ func (s *roFolder) Stop() {
 	close(s.stop)
 }
 
+func (s *roFolder) IndexUpdated() {
+}
+
 func (s *roFolder) String() string {
 	return fmt.Sprintf("roFolder/%s@%p", s.folder, s)
 }

internal/model/rwfolder.go

@@ -32,7 +32,7 @@ import (
 const (
 	pauseIntv     = 60 * time.Second
 	nextPullIntv  = 10 * time.Second
-	checkPullIntv = 1 * time.Second
+	shortPullIntv = 5 * time.Second
 )
 
 // A pullBlockState is passed to the puller routine for each block that needs
@@ -71,12 +71,13 @@ type rwFolder struct {
 	shortID       uint64
 	order         config.PullOrder
 
-	stop      chan struct{}
-	queue     *jobQueue
-	dbUpdates chan protocol.FileInfo
-	scanTimer *time.Timer
-	pullTimer *time.Timer
-	delayScan chan time.Duration
+	stop        chan struct{}
+	queue       *jobQueue
+	dbUpdates   chan protocol.FileInfo
+	scanTimer   *time.Timer
+	pullTimer   *time.Timer
+	delayScan   chan time.Duration
+	remoteIndex chan struct{} // An index update was received, we should re-evaluate needs
 }
 
 func newRWFolder(m *Model, shortID uint64, cfg config.FolderConfiguration) *rwFolder {
@@ -99,11 +100,12 @@ func newRWFolder(m *Model, shortID uint64, cfg config.FolderConfiguration) *rwFo
 		shortID:       shortID,
 		order:         cfg.Order,
 
-		stop:      make(chan struct{}),
-		queue:     newJobQueue(),
-		pullTimer: time.NewTimer(checkPullIntv),
-		scanTimer: time.NewTimer(time.Millisecond), // The first scan should be done immediately.
-		delayScan: make(chan time.Duration),
+		stop:        make(chan struct{}),
+		queue:       newJobQueue(),
+		pullTimer:   time.NewTimer(shortPullIntv),
+		scanTimer:   time.NewTimer(time.Millisecond), // The first scan should be done immediately.
+		delayScan:   make(chan time.Duration),
+		remoteIndex: make(chan struct{}, 1), // This needs to be 1-buffered so that we queue a notification if we're busy doing a pull when it comes.
 	}
 }
 
@@ -149,11 +151,13 @@ func (p *rwFolder) Serve() {
 		case <-p.stop:
 			return
 
-		// TODO: We could easily add a channel here for notifications from
-		// Index(), so that we immediately start a pull when new index
-		// information is available. Before that though, I'd like to build a
-		// repeatable benchmark of how long it takes to sync a change from
-		// device A to device B, so we have something to work against.
+		case <-p.remoteIndex:
+			prevVer = 0
+			p.pullTimer.Reset(shortPullIntv)
+			if debug {
+				l.Debugln(p, "remote index updated, rescheduling pull")
+			}
+
 		case <-p.pullTimer.C:
 			if !initialScanCompleted {
 				if debug {
@@ -183,7 +187,7 @@ func (p *rwFolder) Serve() {
 				if debug {
 					l.Debugln(p, "skip (curVer == prevVer)", prevVer)
 				}
-				p.pullTimer.Reset(checkPullIntv)
+				p.pullTimer.Reset(nextPullIntv)
 				continue
 			}
 
@@ -282,6 +286,17 @@ func (p *rwFolder) Stop() {
 	close(p.stop)
 }
 
+func (p *rwFolder) IndexUpdated() {
+	select {
+	case p.remoteIndex <- struct{}{}:
+	default:
+		// We might be busy doing a pull and thus not reading from this
+		// channel. The channel is 1-buffered, so one notification will be
+		// queued to ensure we recheck after the pull, but beyond that we must
+		// make sure to not block index receiving.
+	}
+}
+
 func (p *rwFolder) String() string {
 	return fmt.Sprintf("rwFolder/%s@%p", p.folder, p)
 }