account/keystore : make fs watcher use not block account ops during fs scan

accounts/keystore/account_cache.go

@@ -209,6 +209,12 @@ func (ac *accountCache) close() {
 // Callers must hold ac.mu.
 func (ac *accountCache) reload() {
 	accounts, err := ac.scan()
+	ac.handleScanResult(accounts, err)
+}
+
+// handleScanResult uses the result of a fs scan to update the account lists
+// This can be used to perform un-mutexed fs scans
+func (ac *accountCache) handleScanResult(accounts []accounts.Account, err error) {
 	if err != nil {
 		log.Debug("Failed to reload keystore contents", "err", err)
 	}

accounts/keystore/watch.go

@@ -99,8 +99,9 @@ func (w *watcher) loop() {
 				hadEvent = true
 			}
 		case <-debounce.C:
+			accounts, err := w.ac.scan()
 			w.ac.mu.Lock()
-			w.ac.reload()
+			w.ac.handleScanResult(accounts, err)
 			w.ac.mu.Unlock()
 			if hadEvent {
 				debounce.Reset(debounceDuration)