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    <p>I think you could use a bit of research into asynchronous calls. Pausing for a certain number of milliseconds is <em>not</em> a safe way to ensure that your callback has been called, and as you said, making <code>verify</code> a field will not work if the object is shared by multiple threads.</p> <p>One option you could use is a <a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Future.html" rel="nofollow"><code>Future&lt;Boolean&gt;</code></a> (in this case, <a href="http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/util/concurrent/SettableFuture.html" rel="nofollow"><code>SettableFuture&lt;Boolean&gt;</code></a> from the Guava libraries is convenient):</p> <pre><code>final SettableFuture&lt;Boolean&gt; verify = new SettableFuture&lt;Boolean&gt;(); p.lookup(lookupKey, new Continuation&lt;PastContent, Exception&gt;() { public void receiveResult(PastContent result) { P2PPKIContent content = (P2PPKIContent) result; if(content !=null){ verify.set(true); } } public void receiveException(Exception result) { System.out.println("Error looking up " + lookupKey); verify.set(false); } }); return verificationQueue.get(); //this will block until verify has been set! </code></pre> <p>A <code>Future&lt;T&gt;</code> is a concurrency construct that will have a value <em>some time in the future</em>. As soon as you ask for its value, however, it will block until it has a value.</p> <h2>Edit</h2> <p>If for some reason you can't pull in Guava, a slightly less intuitive solution is to use a <a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html" rel="nofollow"><code>BlockingQueue&lt;Boolean&gt;</code></a> with a capacity of 1:</p> <pre><code>final BlockingQueue&lt;Boolean&gt; verificationQueue = new ArrayBlockingQueue&lt;Boolean&gt;(1); p.lookup(lookupKey, new Continuation&lt;PastContent, Exception&gt;() { public void receiveResult(PastContent result) { P2PPKIContent content = (P2PPKIContent) result; if(content !=null){ verificationQueue.put(true); } } public void receiveException(Exception result) { System.out.println("Error looking up " + lookupKey); verificationQueue.put(false); } }); return verify.take(); //blocks until an item has been put on the queue </code></pre> <p>If you're going to do this, it's worth encapsulating the queue in a class with a more readable API.</p>
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    1. USMark Peters
    1. USMark Peters
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    1. COGreat..thank you..I tried something similar using an array..but found out fairly quickly this was not a good way to go..I'll get working..much appreciation
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    2. COIn case anyones reading up on this..I had a little difficulty with the first approach Mark listed..Second one worked perfectly straight away..Thanks a lot @Mark helped me greatly
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