Do not assign multiple `exit` handlers for FA

lib/appenders/file.js

@@ -5,6 +5,9 @@ var layouts = require('../layouts')
 , os = require('os')
 , eol = os.EOL || '\n';
 
+var openFiles = [];
+var listenerAtttached = false;
+
 /**
  * File Appender writing the logs to a text file. Supports rolling of logs by size.
  *
@@ -42,10 +45,18 @@ function fileAppender (file, layout, logSize, numBackups) {
 
     var logFile = openTheStream(file, logSize, numBackups);
 
+    // push file to the stack of open handlers
+    openFiles.push(logFile);
+
     //close the file on process exit.
-    process.on('exit', function() {
+    if (!listenerAtttached) {
-        logFile.end();
+        listenerAtttached = true;
-    });
+        process.on('exit', function() {
+            openFiles.forEach(function (file) {
+                file.end();
+            });
+        });
+    }
 
     return function(loggingEvent) {
         logFile.write(layout(loggingEvent) + eol, "utf8");