diff --git a/apigee_sync.go b/apigee_sync.go
index d6b3a19..5c77056 100644
--- a/apigee_sync.go
+++ b/apigee_sync.go
@@ -33,8 +33,8 @@
 		return
 	}
 
-	downloadBootSnapshot(nil)
-	downloadDataSnapshot(quitPollingSnapshotServer)
+	snapManager.downloadBootSnapshot()
+	snapManager.downloadDataSnapshot()
 
 	changeManager.pollChangeWithBackoff()
 
diff --git a/changes.go b/changes.go
index aa8d822..0ac39b2 100644
--- a/changes.go
+++ b/changes.go
@@ -51,9 +51,11 @@
 	}
 	// not launched
 	if atomic.LoadInt32(c.isLaunched) == int32(0) {
-		log.Error("pollChangeManager: close() called when pollChangeWithBackoff unlaunched! close tokenManager!")
+		log.Error("pollChangeManager: close() called when pollChangeWithBackoff unlaunched! Will wait until pollChangeWithBackoff is launched and then kill it and tokenManager!")
 		go func() {
+			c.quitChan <- true
 			tokenManager.close()
+			<-snapManager.close()
 			finishChan <- false
 			log.Debug("change manager closed")
 		}()
@@ -64,6 +66,7 @@
 	go func() {
 		c.quitChan <- true
 		tokenManager.close()
+		<-snapManager.close()
 		finishChan <- true
 		log.Debug("change manager closed")
 	}()
@@ -75,11 +78,6 @@
  */
 
 func (c *pollChangeManager) pollChangeWithBackoff() {
-	// closed
-	if atomic.LoadInt32(c.isClosed) == int32(1) {
-		log.Error("pollChangeManager: pollChangeWithBackoff() called after closed")
-		return
-	}
 	// has been launched before
 	if atomic.SwapInt32(c.isLaunched, 1) == int32(1) {
 		log.Error("pollChangeManager: pollChangeWithBackoff() has been launched before")
@@ -267,7 +265,7 @@
 	}
 	if _, ok := err.(changeServerError); ok {
 		log.Info("Detected DDL changes, going to fetch a new snapshot to sync...")
-		downloadDataSnapshot(c.quitChan)
+		snapManager.downloadDataSnapshot()
 	} else {
 		log.Debugf("Error connecting to changeserver: %v", err)
 	}
diff --git a/init.go b/init.go
index e1b31c5..50ed49d 100644
--- a/init.go
+++ b/init.go
@@ -30,15 +30,15 @@
 
 var (
 	/* All set during plugin initialization */
-	log                       apid.LogService
-	config                    apid.ConfigService
-	dataService               apid.DataService
-	events                    apid.EventsService
-	apidInfo                  apidInstanceInfo
-	newInstanceID             bool
-	tokenManager              *tokenMan
-	changeManager             *pollChangeManager
-	quitPollingSnapshotServer chan bool
+	log           apid.LogService
+	config        apid.ConfigService
+	dataService   apid.DataService
+	events        apid.EventsService
+	apidInfo      apidInstanceInfo
+	newInstanceID bool
+	tokenManager  *tokenMan
+	changeManager *pollChangeManager
+	snapManager   *snapShotManager
 
 	/* Set during post plugin initialization
 	 * set this as a default, so that it's guaranteed to be valid even if postInitPlugins isn't called
@@ -76,7 +76,7 @@
 	events = services.Events()
 	//TODO listen for arbitrary commands, these channels can be used to kill polling goroutines
 	//also useful for testing
-	quitPollingSnapshotServer = make(chan bool)
+	snapManager = createSnapShotManager()
 	changeManager = createChangeManager()
 
 	// set up default database
diff --git a/snapshot.go b/snapshot.go
index ae667bf..0158871 100644
--- a/snapshot.go
+++ b/snapshot.go
@@ -12,17 +12,93 @@
 	"io/ioutil"
 	"net/url"
 	"path"
+	"sync/atomic"
 	"time"
 )
 
+type snapShotManager struct {
+	// to send quit signal to the downloading thread
+	quitChan chan bool
+	// to mark the graceful close of snapshotManager
+	finishChan chan bool
+	// 0 for not closed, 1 for closed
+	isClosed *int32
+	// make sure close() returns immediately if there's no downloading/processing snapshot
+	isDownloading *int32
+}
+
+func createSnapShotManager() *snapShotManager {
+	isClosedInt := int32(0)
+	isDownloadingInt := int32(0)
+	return &snapShotManager{
+		quitChan:      make(chan bool, 1),
+		finishChan:    make(chan bool, 1),
+		isClosed:      &isClosedInt,
+		isDownloading: &isDownloadingInt,
+	}
+}
+
+/*
+ * thread-safe close of snapShotManager
+ * It marks status as closed immediately, and quits backoff downloading
+ * use <- close() for blocking close
+ * should only be called by pollChangeManager, because pollChangeManager is dependent on it
+ */
+func (s *snapShotManager) close() <-chan bool {
+	//has been closed before
+	if atomic.SwapInt32(s.isClosed, 1) == int32(1) {
+		log.Error("snapShotManager: close() called on a closed snapShotManager!")
+		go func() {
+			s.finishChan <- false
+			log.Debug("change manager closed")
+		}()
+		return s.finishChan
+	}
+	s.quitChan <- true
+	// wait until no downloading
+	for atomic.LoadInt32(s.isDownloading) == int32(1) {
+		time.Sleep(time.Millisecond)
+	}
+	s.finishChan <- true
+	return s.finishChan
+}
+
 // retrieve boot information: apid_config and apid_config_scope
-func downloadBootSnapshot(quitPolling chan bool) {
+func (s *snapShotManager) downloadBootSnapshot() {
+	if atomic.SwapInt32(s.isDownloading, 1) == int32(1) {
+		log.Panic("downloadBootSnapshot: only 1 thread can download snapshot at the same time!")
+		return
+	}
+	defer atomic.StoreInt32(s.isDownloading, int32(0))
+
+	// has been closed
+	if atomic.LoadInt32(s.isClosed) == int32(1) {
+		log.Warn("snapShotManager: downloadBootSnapshot called on closed snapShotManager")
+		return
+	}
+
 	log.Debug("download Snapshot for boot data")
 
 	scopes := []string{apidInfo.ClusterID}
 	snapshot := &common.Snapshot{}
-	downloadSnapshot(scopes, snapshot, quitPolling)
-	storeBootSnapshot(snapshot)
+  
+	err := s.downloadSnapshot(scopes, snapshot)
+	if err != nil {
+		// this may happen during shutdown
+		if _, ok := err.(quitSignalError); ok {
+			log.Warn("downloadBootSnapshot failed due to shutdown: " + err.Error())
+		}
+		return
+	}
+
+	// has been closed
+	if atomic.LoadInt32(s.isClosed) == int32(1) {
+		log.Error("snapShotManager: processSnapshot called on closed snapShotManager")
+		return
+	}
+
+	// note that for boot snapshot case, we don't need to inform plugins as they'll get the data snapshot
+  storeBootSnapshot(snapshot)
 }
 
 func storeBootSnapshot(snapshot *common.Snapshot) {
@@ -30,13 +106,32 @@
 }
 
 // use the scope IDs from the boot snapshot to get all the data associated with the scopes
-func downloadDataSnapshot(quitPolling chan bool) {
+func (s *snapShotManager) downloadDataSnapshot() {
+	if atomic.SwapInt32(s.isDownloading, 1) == int32(1) {
+		log.Panic("downloadDataSnapshot: only 1 thread can download snapshot at the same time!")
+		return
+	}
+	defer atomic.StoreInt32(s.isDownloading, int32(0))
+
+	// has been closed
+	if atomic.LoadInt32(s.isClosed) == int32(1) {
+		log.Warn("snapShotManager: downloadDataSnapshot called on closed snapShotManager")
+		return
+	}
+
 	log.Debug("download Snapshot for data scopes")
 
 	scopes := findScopesForId(apidInfo.ClusterID)
 	scopes = append(scopes, apidInfo.ClusterID)
 	snapshot := &common.Snapshot{}
-	downloadSnapshot(scopes, snapshot, quitPolling)
+	err := s.downloadSnapshot(scopes, snapshot)
+	if err != nil {
+		// this may happen during shutdown
+		if _, ok := err.(quitSignalError); ok {
+			log.Warn("downloadDataSnapshot failed due to shutdown: " + err.Error())
+		}
+		return
+	}
 	storeDataSnapshot(snapshot)
 }
 
@@ -47,6 +142,12 @@
 	if err != nil {
 		log.Panicf("Database inaccessible: %v", err)
 	}
+
+	// if closed
+	if atomic.LoadInt32(s.isClosed) == int32(1) {
+		log.Warn("Trying to persistKnownTablesToDB with a closed snapShotManager")
+		return
+	}
 	persistKnownTablesToDB(knownTables, db)
 
 	log.Info("Emitting Snapshot to plugins")
@@ -55,6 +156,8 @@
 	case <-time.After(pluginTimeout):
 		log.Panic("Timeout. Plugins failed to respond to snapshot.")
 	case <-events.Emit(ApigeeSyncEventSelector, snapshot):
+		// the new snapshot has been processed
+		// if close() happen after persistKnownTablesToDB(), will not interrupt snapshot processing to maintain consistency
 	}
 
 }
@@ -119,8 +222,15 @@
 	}
 }
 
+// a blocking method
 // will keep retrying with backoff until success
-func downloadSnapshot(scopes []string, snapshot *common.Snapshot, quitPolling chan bool) {
+
+func (s *snapShotManager) downloadSnapshot(scopes []string, snapshot *common.Snapshot) error {
+	// if closed
+	if atomic.LoadInt32(s.isClosed) == int32(1) {
+		log.Warn("Trying to download snapshot with a closed snapShotManager")
+		return quitSignalError{}
+	}
 
 	log.Debug("downloadSnapshot")
 
@@ -147,8 +257,8 @@
 	//pollWithBackoff only accepts function that accept a single quit channel
 	//to accomadate functions which need more parameters, wrap them in closures
 	attemptDownload := getAttemptDownloadClosure(client, snapshot, uri)
-
-	pollWithBackoff(quitPolling, attemptDownload, handleSnapshotServerError)
+	pollWithBackoff(s.quitChan, attemptDownload, handleSnapshotServerError)
+	return nil
 }
 
 func getAttemptDownloadClosure(client *http.Client, snapshot *common.Snapshot, uri string) func(chan bool) error {