[SPARK-12701][CORE] FileAppender should use join to ensure writing thread completion

Changed Logging FileAppender to use join in `awaitTermination` to ensure that thread is properly finished before returning.

Author: Bryan Cutler <cutlerb@gmail.com>

Closes #10654 from BryanCutler/fileAppender-join-thread-SPARK-12701.

core/src/main/scala/org/apache/spark/util/logging/FileAppender.scala

@@ -29,7 +29,6 @@ private[spark] class FileAppender(inputStream: InputStream, file: File, bufferSi
   extends Logging {
   @volatile private var outputStream: FileOutputStream = null
   @volatile private var markedForStop = false     // has the appender been asked to stopped
-  @volatile private var stopped = false           // has the appender stopped
 
   // Thread that reads the input stream and writes to file
   private val writingThread = new Thread("File appending thread for " + file) {
@@ -47,11 +46,7 @@ private[spark] class FileAppender(inputStream: InputStream, file: File, bufferSi
    * or because of any error in appending
    */
   def awaitTermination() {
-    synchronized {
-      if (!stopped) {
-        wait()
-      }
-    }
+    writingThread.join()
   }
 
   /** Stop the appender */
@@ -77,10 +72,6 @@ private[spark] class FileAppender(inputStream: InputStream, file: File, bufferSi
         logError(s"Error writing stream to file $file", e)
     } finally {
       closeFile()
-      synchronized {
-        stopped = true
-        notifyAll()
-      }
     }
   }