watcher: ignore CHMOD, limit WaitForReplacement, longer sleep

fix "done" chan, only used by tests:
the "break" just broke out of the select block, no the for loop
could use a label, simplest fix is to just return

simpler handling of CHMOD: just ignore it (if not also a rename or remove)

limit WaitForReplacement to about 2 seconds
(instead of waiting forever for file to re-appear)

WaitForReplacement sleeps first before re-checking, for 100ms (longer)
(makes travis-ci tests less flakey)

watcher.go

@@ -11,23 +11,18 @@ import (
 	"github.com/fsnotify/fsnotify"
 )
 
-func WaitForReplacement(filename string, op fsnotify.Op,
-	watcher *fsnotify.Watcher) {
-	const sleep_interval = 50 * time.Millisecond
+func WaitForReplacement(filename string, watcher *fsnotify.Watcher) {
+	for i := 0; i < 20; i++ {
+		time.Sleep(100 * time.Millisecond)
 
-	// Avoid a race when fsnofity.Remove is preceded by fsnotify.Chmod.
-	if op&fsnotify.Chmod != 0 {
-		time.Sleep(sleep_interval)
-	}
-	for {
 		if _, err := os.Stat(filename); err == nil {
 			if err := watcher.Add(filename); err == nil {
 				log.Printf("watching resumed for %s", filename)
 				return
 			}
 		}
-		time.Sleep(sleep_interval)
 	}
+	log.Printf("failed to resume watching for %s", filename)
 }
 
 func WatchForUpdates(filename string, done <-chan bool, action func()) {
@@ -37,22 +32,22 @@ func WatchForUpdates(filename string, done <-chan bool, action func()) {
 		log.Fatal("failed to create watcher for ", filename, ": ", err)
 	}
 	go func() {
-		defer watcher.Close()
 		for {
 			select {
 			case _ = <-done:
 				log.Printf("Shutting down watcher for: %s", filename)
-				break
+				watcher.Close()
+				return
 			case event := <-watcher.Events:
 				// On Arch Linux, it appears Chmod events precede Remove events,
 				// which causes a race between action() and the coming Remove event.
-				// If the Remove wins, the action() (which calls
-				// UserMap.LoadAuthenticatedEmailsFile()) crashes when the file
-				// can't be opened.
-				if event.Op&(fsnotify.Remove|fsnotify.Rename|fsnotify.Chmod) != 0 {
+				if event.Op == fsnotify.Chmod {
+					continue
+				}
+				if event.Op&(fsnotify.Remove|fsnotify.Rename) != 0 {
 					log.Printf("watching interrupted on event: %s", event)
 					watcher.Remove(filename)
-					WaitForReplacement(filename, event.Op, watcher)
+					WaitForReplacement(filename, watcher)
 				}
 				log.Printf("reloading after event: %s", event)
 				action()