Change locking behavior to assure correct transaction ordering, stop storing eTag in DB

api.go

diff --git a/api.go b/api.go
index e677294..fec8239 100644
--- a/api.go
+++ b/api.go
@@ -6,10 +6,11 @@
 	"fmt"
 	"io/ioutil"
 	"net/http"
-	"strconv"
-	"time"
-	"sync"
 	"net/url"
+	"strconv"
+	"sync"
+	"sync/atomic"
+	"time"
 )
 
 const (
@@ -23,6 +24,7 @@
 var (
 	deploymentsChanged = make(chan string)
 	addSubscriber      = make(chan chan string)
+	eTag               int64
 )
 
 type errorResponse struct {
@@ -94,13 +96,14 @@
 			subscribers = make(map[chan string]struct{})
 			m := msg
 			msg = ""
+			incrementETag()
 			mut.Unlock()
 			log.Debugf("Delivering deployment change %s to %d subscribers", m, len(subs))
-			incrementETag()
 			for subscriber := range subs {
 				select {
 				case subscriber <- m:
 					log.Debugf("Handling deploy response for: %s", m)
+					log.Debugf("delivering TO: %v", subscriber)
 				default:
 					log.Debugf("listener too far behind, message dropped")
 				}
@@ -153,11 +156,7 @@
 	log.Debugf("if-none-match: %s", ifNoneMatch)
 
 	// send unmodified if matches prior eTag and no timeout
-	eTag, err := getETag()
-	if err != nil {
-		writeDatabaseError(w)
-		return
-	}
+	eTag := getETag()
 	if eTag == ifNoneMatch && timeout == 0 {
 		w.WriteHeader(http.StatusNotModified)
 		return
@@ -210,16 +209,16 @@
 
 	for _, d := range dataDeps {
 		apiDeps = append(apiDeps, ApiDeployment{
-			ID:                d.ID,
-			ScopeId:           d.DataScopeID,
-			Created:           d.Created,
-			CreatedBy:         d.CreatedBy,
-			Updated:           d.Updated,
-			UpdatedBy:         d.UpdatedBy,
-			BundleConfigJson:  []byte(d.BundleConfigJSON),
-			ConfigJson:        []byte(d.ConfigJSON),
-			DisplayName:       d.BundleName,
-			URI:               d.LocalBundleURI,
+			ID:               d.ID,
+			ScopeId:          d.DataScopeID,
+			Created:          d.Created,
+			CreatedBy:        d.CreatedBy,
+			Updated:          d.Updated,
+			UpdatedBy:        d.UpdatedBy,
+			BundleConfigJson: []byte(d.BundleConfigJSON),
+			ConfigJson:       []byte(d.ConfigJSON),
+			DisplayName:      d.BundleName,
+			URI:              d.LocalBundleURI,
 		})
 	}
 
@@ -329,3 +328,13 @@
 		return nil
 	}
 }
+
+// call whenever the list of deployments changes
+func incrementETag() {
+	atomic.AddInt64(&eTag, 1)
+}
+
+func getETag() string {
+	e := atomic.LoadInt64(&eTag)
+	return strconv.FormatInt(e, 10)
+}

data.go

diff --git a/data.go b/data.go
index 6cd175a..dc46ab7 100644
--- a/data.go
+++ b/data.go
@@ -39,10 +39,6 @@
 
 func InitDB(db apid.DB) error {
 	_, err := db.Exec(`
-	CREATE TABLE IF NOT EXISTS etag (
-		value integer
-	);
-	INSERT INTO etag (value) VALUES (1);
 	CREATE TABLE IF NOT EXISTS deployments (
 		id character varying(36) NOT NULL,
 		bundle_config_id varchar(36) NOT NULL,
@@ -88,42 +84,6 @@
 	unsafeDB = db
 }
 
-// call whenever the list of deployments changes
-func incrementETag() error {
-
-	stmt, err := getDB().Prepare("UPDATE etag SET value = value+1;")
-	if err != nil {
-		log.Errorf("prepare update etag failed: %v", err)
-		return err
-	}
-	defer stmt.Close()
-
-	_, err = stmt.Exec()
-	if err != nil {
-		log.Errorf("update etag failed: %v", err)
-		return err
-	}
-
-	log.Debugf("etag incremented")
-	return err
-}
-
-func getETag() (string, error) {
-
-	var eTag string
-	db := getDB()
-	row := db.QueryRow("SELECT value FROM etag")
-	err := row.Scan(&eTag)
-	//err := getDB().QueryRow("SELECT value FROM etag").Scan(&eTag)
-	if err != nil {
-		log.Errorf("select etag failed: %v", err)
-		return "", err
-	}
-
-	log.Debugf("etag queried: %v", eTag)
-	return eTag, err
-}
-
 func InsertDeployment(tx *sql.Tx, dep DataDeployment) error {
 
 	log.Debugf("insertDeployment: %s", dep.ID)

listener.go

diff --git a/listener.go b/listener.go
index 7d9b056..24f3d96 100644
--- a/listener.go
+++ b/listener.go
@@ -64,6 +64,7 @@
 
 	// ensure that no new database updates are made on old database
 	dbMux.Lock()
+	defer dbMux.Unlock()
 
 	defer tx.Rollback()
 	for _, table := range snapshot.Tables {
@@ -86,7 +87,6 @@
 	}
 
 	SetDB(db)
-	dbMux.Unlock()
 
 	// if no tables, this a startup event for an existing DB, start bundle downloads that didn't finish
 	if len(snapshot.Tables) == 0 {
@@ -109,6 +109,11 @@
 		log.Panicf("Error processing ChangeList: %v", err)
 	}
 	defer tx.Rollback()
+
+	// ensure bundle download and delete updates aren't attempted while in process
+	dbMux.Lock()
+	defer dbMux.Unlock()
+
 	var bundlesToDelete []string
 	for _, change := range changes.Changes {
 		var err error