How to create a method that accepts a callback function in java?

Question

I created a distributed lock class that I designed to be used like this:

myLock.lock();
doSomething();
myLock.unlock();

In my current implementation, lock() blocks until the lock is acquired. But I am running into some deadlock issues with this implementation. So I'd like to rewrite it to be asynchronous, but I have no idea how to do that in java.

Something like this would work I think:

myLock.lock(myCallbackFunction);

private void myCallbackFunction(boolean result){
    if(result){
        doSomething();
        mylock.Unlock();
    }
}

Is there a way to do this in java?

EDIT (More detail): The reasons why the synchronous implementation is deadlocking are complicated and not relevant. The distributed lock is acquiring mutual exclusion of a resource across a network with multiple systems. Really the only thing I'm looking for is how to write a method that accepts a callback function.

"So I'd like to rewrite it to be asynchronous" - A lock is synchronous by definition. What do you mean by "I'd like to rewrite it to be asynchronous"? — Mitch Wheat
– Mitch Wheat, Commented Mar 4, 2013 at 2:56
You should provide more details about these methods. When exactly are you getting the deadlock? — Yuri
– Yuri, Commented Mar 4, 2013 at 2:58
You need to start a thread, or use one of the thread pool facilities. — Hot Licks
– Hot Licks, Commented Mar 4, 2013 at 3:07

jacobm · Accepted Answer · 2013-03-04 14:45:38Z

3

You can't do that in Java yet. What you can do is define a LockCallback interface:

interface LockCallback {
  void run(boolean result, MyLock lock);
}

and have MyLock#lock take a LockCallback as a parameter. Then callers can call it as

myLock.lock(new LockCallback {
  public void run(boolean result, MyLock lock) {
    // ... do whatever needs to be done ...
    lock.unlock();
  });

Lambda syntax in Java 8 should make this a little less ugly looking.

edited Mar 4, 2013 at 14:45

answered Mar 4, 2013 at 3:54

jacobm

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Comments

Ryan Stewart · Accepted Answer · 2013-03-04 03:05:17Z

0

Instead of writing your own and then abandoning the idea because you couldn't make it work, why not use a Semaphore, which is already there and is implemented correctly?

answered Mar 4, 2013 at 3:05

Ryan Stewart

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2 Comments

Hot Licks Over a year ago

Still doesn't make anything asynchronous.

Ryan Stewart Over a year ago

@HotLicks: True, but while the question's title is about asynchronous methods, that's not what the content of the question talks about.

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