Re: wait finishes early?

From:

"Mike Schilling" <mscottschilling@hotmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 8 Dec 2009 20:54:38 -0800

Message-ID:

<hfnaig$v9v$1@news.eternal-september.org>

John B. Matthews wrote:

In article
<d331b09d-80b6-4eda-9bda-865bf24dc6b3@r40g2000yqn.googlegroups.com>,
mikew01 <mikew01@blueyonder.co.uk> wrote:

I am trying to write a method that detects when a thread has timed
out waiting for a resource, for brevity I have included the
important
parts below in the lock method. I am finding that when I specify a
value of around 6000ms and above the period is calculated lower
than
the timeout which results in the code thinking that the thread has
not timed out waiting but has simply been released from a notify.
It appears that either wait( timeout ) is releasing early or I am
not
using the correct method for gauging the time to obtain period.
[...]
synchronized ( requester )
{
requester.wait( timeout );
}

[...]

"Always invoke wait inside a loop that tests for the condition being
waited for."

<http://java.sun.com/docs/books/tutorial/essential/concurrency/guardmeth.
html>
<http://java.sun.com/javase/6/docs/api/java/lang/Object.html#wait(long)>
<http://www.javaconcurrencyinpractice.com/>

This looks to me like the correct logic, encapsulated reasonably well:

public class EventUtils
{
    public static void waitforEvent(
            long maxDelay, Object lock, EventChecker checker)
                throws InterruptedException
    {
        synchronized(lock)
        {
            long start = System.currentTimeMillis();
            long toWait = maxDelay;
            while (true)
            {
                lock.wait(toWait);
                if (checker.isDone())
                    break;
                if (maxDelay > 0)
                {
                    long elapsed = System.currentTimeMillis() - start;
                    if (elapsed >= maxDelay)
                        break;
                    toWait = maxDelay - elapsed;
                }
            }
        }
    }

    public interface EventChecker
    {
        boolean isDone();
    }
}