Question

I have a method, say method1(), that takes a while to run. During it’s execution, if there is another call to method1(), it should be ignored. I have, roughly, something like this

    boolean mFlag = false;

    void method1()
    {
        if(!mFlag)
        {
           mFlag=true;

           // do Stuff

          mFlag=false;
        }
    }

This works. But I was wondering if there is a better way to do this preferably not involving any flags.

Answer 1

Yes, you should really be using something from java.util.concurrent.locks Your example isn’t quite strictly correct, that boolean needs to be volatile.

ReentrantLock lock = new ReentrantLock();

    void method1()
    {
        if(lock.tryLock())
        {
           try {
             if (!(lock.getHoldCount() > 1)) {
               //do Some Stuff
             }
          } finally {
            lock.unlock();
          }
        }
    }

Edited to handle skipping execution on reentrance as inidicated in your comment. Unfortunatly there isn’t really a great way to do that with the built in library, as it’s a bit of an odd usecase, but I still think using the built in library is a better option.