Question

I am implementing a method that updates UI and can be executed either from the UI thread or from other threads. According to Javadocs, in the latter case Display.syncExec() or Display.asyncExec() methods should be used. Do I have to check whether my method is executed in the UI thread or syncExec/asyncExec is suitable for both cases?

Answer 1

Executing Display.syncExec/asyncExec is safe from any thread (including the UI thread), but it isn’t always the best route. For instance, asyncExec will always add your runnable into the queue to execute later even if you are already on the UI thread. Depending on your usecase, that may or may not be desirable. Often, if you known you are already on the UI thread, it is better to just go ahead and execute the work item.

I like to use the following snippet in any method that needs to update UI and may be called from a non-UI thread. If called from UI thread, it executes the work immediately. If called from other thread, it uses asyncExec to schedule work in the next batch without blocking the calling thread.

public void task()
{
    if( this.display.getThread() != Thread.currentThread() )
    {
        this.display.asyncExec
        (
            new Runnable()
            {
                public void run()
                {
                    task();
                }
            }
        );

        return;
    }

    // Do whatever needs to be done with the UI.
}