Java loop for a certain duration

Question

Hi,

Is there a way I can do a for loop for a certain amount of time easily? (without measuring the time ourselves using System.currentTimeMillis() ?)

I.e. I want to do something like this in Java:

int x = 0;
for( 2 minutes )  {
   System.out.println(x++);
}

Thanks

Answer 1

No. That is sort of a strange request considering how simple it would be to simply write a function that uses System.currentTimeMillis() (or whichever time function you choose). More context of the situation might be in order.

Answer 2

I don't think there is a way to loop for a certain period of time without checking to see if you've looped for a certain period of time.

Answer 3

Depending on your use case either of the two sleep() methods in class Thread might fit the bill, but it sounds like you have to fuss with System.currentTimeMillis(), which seems strange.

Thread thread = Thread.currentThread();
thread.sleep(10);      // 10 milliseconds
thread.sleep(12, 345); // 12 milliseconds and 345 nanoseconds.

Answer 4

Loops iterate over value comparison and not for duration. So without yourself assigning and comparing the system time, you cannot do it. If however you wish it be intuitive, then you can have a function that internally uses milliseconds, but takes Minutes as argument and use it.

And No, you cannot use threads or the sleep method in it, because that does not ensure the exact time. If your processor is busy with some other thread after the given time elapses, then your thread will continue to wait.

Answer 5

No, there isn't a built-in construct which does that.

I want to point out that you should not use System.currentTimeMillis() for performing, or delaying, a task for a specified time period. Instead use System.nanoTime(). The former method is inaccurate in Windows, while the latter method is accurate regardless of OS. You can use TimeUnit enum to easily go between time in milliseconds, or any other time unit, to time in nanoseconds.

        for (long stop=System.nanoTime()+TimeUnit.SECONDS.toNanos(2);stop>System.nanoTime();) {
        /*
         * Hammer the JVM with junk
         */
        }

Answer 6

I think that this is what you want:

private final Thread thisThread = Thread.current();
private final int timeToRun = 120000; // 2 minutes;

new Thread(new Runnable() {
    public void run() {
        sleep(timeToRun);
        thisThread.interrupt();
    }).start();

while (!Thread.interrupted()) {
    // do something interesting.
}

This avoids doing repeated syscalls to get the system clock value (which can be rather expensive) and polls the current thread's interrupted flag instead (much cheaper).

EDIT

There is actually no safe alternative to polling the clock or polling a flag. In theory, you could modify the above fragment to call the deprecated Thread.stop() method instead of Thread.interrupt().

(I do NOT recommend using Thread.stop() and friends. They are flawed, and dangerous to use. I'm just posing this as a theoretical alternative.)

EDIT 2

Just to point out that using Thread.interrupt() has the advantages over setting a shared flag:

• Thread.interrupt() will cause certain blocking I/O and synchronization methods to unblock and throw a checked exception. Updating a shared flag won't do this.

• Some third-party libraries also check the interrupt flag to see if they should stop what they are currently doing.

• If your loop involves calls to other methods, etc, Thread.interrupt() means that you don't need to worry about those methods can access the flag ... if they need to.

EDIT 3

Just to add that sleep(N) is not guaranteed to wake the sleeping thread up after exactly N milliseconds. But under normal circumstances, it will be reasonably close.