'Do I need synchronization if I reference objects from other thread to AWT thread?

Does SwingUtilities.invokeLater provides synchronization?

Example:

public class Threads {
    public static void main(String[] args) {
        new Thread(new Runnable() {     
            @Override
            public void run() {
                new Threads().test();
            }
        }).start();
    }
    
    List<Integer> list = new ArrayList<>(); 
    
    void test() {
        System.out.println(Thread.currentThread().toString());  
        
        for (int i=0; i<10000000; i++) {
            list.add(i);
        }
        
        SwingUtilities.invokeLater(() -> {                          
            System.out.println(Thread.currentThread().toString());
            list.forEach(System.out::println);  // list auto synchronized?      
        });
    }
}

Would be list synchronized when I read values from the list in AWT thread?

javamultithreadingswing


Solution 1:[1]

Does SwingUtilities.invokeLater provides synchronization?

No. It just runs its parameter later.

Would be list synchronized when I read values from the list in AWT thread?

No, but it doesn't need to be. It is sent to invokeLater after it was created and assigned with values. It doesn't change at any later time so it won't be changed while the code sent to invokeLater is executed.

Solution 2:[2]

To summarize some facts:

  • in general Swing is not threadsafe
  • everything GUI-related runs on the awt Event Dispatching Thread
  • EDT does not guarantee the order of execution
  • EDT dispatches time-consuming work to worker threads (> worker pattern)
  • EDT should execute only small GUI-related tasks otherwise UI will freeze
  • SwingUtilities.invokeLater is based on awt.EventQueue.invokeLater

So if you have SwingUtilities.invokeLater and give it a Runnable (your function), this Runnable will be put into an event-queue for the dispachter thread (EDT) which will execute your Runnable asynchronously.

To be exact:

Yes, your code as part of invokeLater will run in parallel (if that is what you meant) on the EDT which runs asychronously to the main thread.

No, it is not synchronized in matter of "another thread entering it" because it is designated only to be executed by the EDT.

Although it is not part of the question: EDT should not be misused in that way. Instead you should put this task into a worker thread and let EDT be for what it has been created: dispatching GUI related tasks to worker threads.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 selalerercapitolis
Solution 2 user3192295

Related Questions