Re: Threading design question

"Daniel Pitts" <>
24 Nov 2006 11:28:07 -0800
Christian Kaufhold wrote:

Daniel Pitts <> wrote:

public void waitToStartProcessing() throws InterruptedException {
    long timeUntilEnd = System.currentTimeMillis() + pollSeconds *
    while (System.currentTimeMillis() < timeUntilEnd) {
          synchronized(waitLock) {
                waitLock.wait(timeUntilEnd -

Danger here: If System.currentTimeMillis() changes between the two calls,
the argument may become zero, which means waiting forever.

Ah, yes. You are absolutely right.

private boolean stillWaiting = true;

public void waitToStartProcessing() throws InterruptedException {
    long timeUntilEnd = System.currentTimeMillis() + pollSeconds *
    long curTime = System.currentTimeMillis() ;
    synchronized(waitLock) {
        while (curTime < timeUntilEnd || stillWaiting) {
            waitLock.wait(timeUntilEnd - curTime);
            curTime = System.currentTimeMillis();

This does not work, you now need an extra flag for that (as usual).

public void forceProcessing() {
   synchronized(waitLock) {
         stillWaiting = false;


I wrote it on the fly, but this version should work much better.

Although, I seem to recall that Lock has a better mechanism for this...
Read that and the Condition class. I believe Condition has an
"awayUntil(Date date)" method, which is exactly what you want.

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