Why myThread.sleep(60000) Hangs Computer?

Question

I have been battling a thread hanging problem in my application for several days now. It appears to be hanging when I tell my second thread to sleep, but not
all the time -- only after about four hours of running does it hang. The application is like a timer/scheduler. You tell it when you want to be notified, say in 60 minutes. It wakes up every 1 minute, updates the progress bars, then goes back to sleep, until 60 minutes has passed... But like I said, on some of the sleeps, it's not waking up. Below is the code that I think is significant...
public class Timer extends JApplet implements Runnable, ActionListener {
* Listens to the user interface buttons for this dialog.
* @param e The action event.
public void actionPerformed(ActionEvent e) {
JButton source = (JButton)e.getSource();
if (source.getActionCommand().equals("Start")) {
timerThread = new Thread(this, "Timer");
timerThread.setPriority(Thread.MIN_PRIORITY);
timerThread.start();
* Start timing the scheduled events.
public void run() {
boolean interrupted = false;
boolean firstTask = true;
while(!interrupted) {
interrupted = !runTask (
"Meal 1", this.mealTimeField0, mealBeginClip, mealEndClip);
interrupted = !runTask(
"Work 1", this.workTimeField0, workBeginClip, workEndClip);
interrupted = !runTask (
"Rest 1", this.restTimeField0,restBeginClip, restEndClip);
//more of the same
interrupted = !runTask (
"Sleep", this.sleepTimeField, sleepBeginClip, sleepEndClip);
private boolean runTask (
String barText, JTextField field, AudioClip beginClip, AudioClip endClip) {
try {
int minutes = stringToPosInt (field.getText());
timerThread.sleep(60 * 1000);
for (int i = 1; i < minutes; ++i) {
System.out.println("before sleep");
timerThread.sleep(60 * 1000); //hangs here??????
System.out.println("after sleep");
} catch (InterruptedException e) {return false;}
return true;
}

Answer 1

When it skips some of the sleeps, does it later wake up again? I'm wondering if it is waking up on some multiple of the sleep period. Apart from the wording of the api docs, I'm not sure if Sun intended to guarantee that sleep would wake up immediately on the specified time. They've always been pretty vague about the required semantics on the implementations of threads in any JVM. I'd guess that something else is going on at the time your thread was due to wake up, like something on the AWT thread, and the thread is getting skipped until the next iteration. Wierd, but its all I can think of.
Try substituting wait(60*1000) for sleep(60*1000).
Also, two other suggestions. Read the "special token" information on this site so that your code will be formatted nicely in the message; makes it easier for others to understand what it does. Also, sleep is a static method, so keep in mind that timerThread.sleep will put the current thread to sleep, whatever that may be. That means you have to be careful not to execute something like that in a method that will be executed by the AWT thread; it won't do what you expected it to do.