ae: ensure that syncs are blocked when paused

agent/ae/ae.go

@@ -2,9 +2,10 @@
 package ae
 
 import (
+	"errors"
 	"log"
 	"math"
-	"sync/atomic"
+	"sync"
 	"time"
 
 	"github.com/hashicorp/consul/lib"
@@ -75,7 +76,8 @@ type StateSyncer struct {
 	SyncChanges *Trigger
 
 	// paused stores whether sync runs are temporarily disabled.
-	paused *toggle
+	pauseLock sync.Mutex
+	paused    bool
 }
 
 func NewStateSyner(state State, intv time.Duration, shutdownCh chan struct{}, logger *log.Logger) *StateSyncer {
@@ -86,7 +88,6 @@ func NewStateSyner(state State, intv time.Duration, shutdownCh chan struct{}, lo
 		Logger:      logger,
 		SyncFull:    NewTrigger(),
 		SyncChanges: NewTrigger(),
-		paused:      new(toggle),
 	}
 }
 
@@ -99,6 +100,8 @@ const (
 	retryFailIntv = 15 * time.Second
 )
 
+var errPaused = errors.New("paused")
+
 // Run is the long running method to perform state synchronization
 // between local and remote servers.
 func (s *StateSyncer) Run() {
@@ -114,13 +117,13 @@ func (s *StateSyncer) Run() {
 FullSync:
 	for {
 		// attempt a full sync
-		if err := s.State.SyncFull(); err != nil {
-			s.Logger.Printf("[ERR] agent: failed to sync remote state: %v", err)
+		err := s.ifNotPausedRun(s.State.SyncFull)
+		if err != nil {
+			if err != errPaused {
+				s.Logger.Printf("[ERR] agent: failed to sync remote state: %v", err)
+			}
 
-			// retry full sync after some time or when a consul
-			// server was added.
 			select {
-
 			// trigger a full sync immediately.
 			// this is usually called when a consul server was added to the cluster.
 			// stagger the delay to avoid a thundering herd.
@@ -162,10 +165,8 @@ FullSync:
 
 			// do partial syncs on demand
 			case <-s.SyncChanges.Notif():
-				if s.Paused() {
-					continue
-				}
-				if err := s.State.SyncChanges(); err != nil {
+				err := s.ifNotPausedRun(s.State.SyncChanges)
+				if err != nil && err != errPaused {
 					s.Logger.Printf("[ERR] agent: failed to sync changes: %v", err)
 				}
 
@@ -176,40 +177,39 @@ FullSync:
 	}
 }
 
+func (s *StateSyncer) ifNotPausedRun(f func() error) error {
+	s.pauseLock.Lock()
+	defer s.pauseLock.Unlock()
+	if s.paused {
+		return errPaused
+	}
+	return f()
+}
+
 // Pause temporarily disables sync runs.
 func (s *StateSyncer) Pause() {
-	s.paused.On()
+	s.pauseLock.Lock()
+	if s.paused {
+		panic("pause while paused")
+	}
+	s.paused = true
+	s.pauseLock.Unlock()
 }
 
 // Paused returns whether sync runs are temporarily disabled.
 func (s *StateSyncer) Paused() bool {
-	return s.paused.IsOn()
+	s.pauseLock.Lock()
+	defer s.pauseLock.Unlock()
+	return s.paused
 }
 
 // Resume re-enables sync runs.
 func (s *StateSyncer) Resume() {
-	s.paused.Off()
-	s.SyncChanges.Trigger()
-}
-
-// toggle implements an on/off switch using methods from the atomic
-// package. Since fields in structs that are accessed via
-// atomic.Load/Add methods need to be aligned properly on some platforms
-// we move that code into a separate struct.
-//
-// See https://golang.org/pkg/sync/atomic/#pkg-note-BUG for details
-type toggle int32
-
-func (p *toggle) On() {
-	atomic.AddInt32((*int32)(p), 1)
-}
-
-func (p *toggle) Off() {
-	if atomic.AddInt32((*int32)(p), -1) < 0 {
-		panic("toggle not on")
+	s.pauseLock.Lock()
+	if !s.paused {
+		panic("resume while not paused")
 	}
-}
-
-func (p *toggle) IsOn() bool {
-	return atomic.LoadInt32((*int32)(p)) > 0
+	s.paused = false
+	s.pauseLock.Unlock()
+	s.SyncChanges.Trigger()
 }