java synchronized方法似乎不起作用

Question

我有修改文件时执行的代码

public class WatchQueueReaderTask<Void> extends Task {
...
                protected Object call() throws Exception {
    try {
        // get the first event before looping
        WatchKey key = myWatcher.take();
        while (key != null) {
            // we have a polled event, now we traverse it and 
            // receive all the states from it
            for (WatchEvent event : key.pollEvents()) {
                WatchEvent.Kind eventType = event.kind();
                if (eventType == OVERFLOW) {
                    continue;
                     }

                    process(event);

                if (isCancelled()) {
                    System.out.println("WatchQueueReaderTask::call isCancelled");
                    return null;
                }
            }
            key.reset();
            key = myWatcher.take();
        }
    } catch (InterruptedException e) {
        ArrayList<WatchFileItem> auxList = threadFileToWatch;
        for (WatchFileItem obj : auxList) {
            if (obj.file != null) {
                try {
                    obj.file.close();
                } catch (IOException ex) {
                    System.out.println("errore in file close");
                    Logger.getLogger(WatchQueueReaderTask.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
        //e.printStackTrace();
    }
    System.out.println("Stopping thread");
    return null;
   }
 ...
 private synchronized void process(WatchEvent evt) {
 ... }
  }

我用它来打电话：

    ThreadFactory processingThreadFactoryForRealtime = null;
    ExecutorService processingThreadFactoryForRealtimeExecutor = null;
    WatchQueueReaderTask mywatchQueueReader = null;

    processingThreadFactoryForRealtime = new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                 Thread t = new Thread(r);
                 t.setName("FileWatcherTask");
                 t.setDaemon(true);
                 return t;
             }
    };  

    processingThreadFactoryForRealtimeExecutor = Executors.newSingleThreadExecutor(processingThreadFactoryForRealtime);
    mywatchQueueReader = new WatchQueueReaderTask(realtimePath, watcherServiceForRealtime, fileToWatchForRealtime); 
    processingThreadFactoryForRealtimeExecutor.execute(mywatchQueueReader);

问题是同时执行多个方法process（）而不等待前一个完成。

我哪里错了？