Merge pull request #70 from Sirupsen/failed-hook-errors

hooks: lock on the logger before printing to stderr, printf args

entry.go

@@ -76,12 +76,16 @@ func (entry *Entry) log(level Level, msg string) {
 	entry.Message = msg
 
 	if err := entry.Logger.Hooks.Fire(level, entry); err != nil {
-		fmt.Fprintf(os.Stderr, "Failed to fire hook\n", err)
+		entry.Logger.mu.Lock()
+		fmt.Fprintf(os.Stderr, "Failed to fire hook: %v\n", err)
+		entry.Logger.mu.Unlock()
 	}
 
 	reader, err := entry.Reader()
 	if err != nil {
+		entry.Logger.mu.Lock()
 		fmt.Fprintf(os.Stderr, "Failed to obtain reader, %v\n", err)
+		entry.Logger.mu.Unlock()
 	}
 
 	entry.Logger.mu.Lock()