Re: Need some guidance on using timer
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Hi Tom,
thanks for your answer, however... (see below)
Tom Hawtin schreef:
Hendrik Maryns wrote:
I have this application which does a rather long computation, possibly
more than exponential in the input. I want to test how far I can go
within reasonable time. So I thought I???d have the program try to
compute stuff for ever bigger inputs, and see how far I got. This used
to work, since the main problem was space, so at a certain moment, an
OOME would occur, which I could catch and start again/continue.
However, now the space problem seems solved, and time is the main
factor. So I want to sort of limit the time the computation takes. I
sort of feel I need to use a Timer for this, and need a separate thread
which interrupts the main one after a certain time. However, I have no
experience at all with multithreading and using Timers, so I would be
very grateful for some guidance on how one could do this.
If you want to interrupt the main thread using the thread interrupt
mechanism, that's easy enough:
public static void main(String[] args) {
final Thread mainThread = Thread.currentThread();
Thread interrupter = new Thread(new Runnable() {
public void run() {
try {
Thread.sleep(120*1000);
mainThread.interrupt();
} catch (java.lang.InterruptedException exc) {
// Just exit.
}
}
});
interrupter.setDaemon(true); // Shouldn't keep process alive.
interrupter.start(); // Important.
... do stuff ...
// Let the interrupted exit, if hasn't already.
interrupter.interrupt();
}
Of course that relies on your main code doing something interruptible:
waits/sleeps and, depending upon implementation, I/O. Interrupts can
also cause class loading to fails, at least theoretically.
Aha, I didn???t know that was necessary. It is definitely CPU that???s
going on. If I read
<http://java.sun.com/javase/6/docs/api/java/lang/Thread.html#interrupt()>,
it is unclear that it is really necessary for the thread to be doing one
of those things. If it is simply running, only a boolean will be set,
which can be asked with Thread.isInterrupted(). That seems sort of the
same system as what you describe below.
However, I don???t like that, since it means I have to do a check in the
running thread. That doesn???t fit my purpose, though it is not
impossible, if need be.
Let me describe my scenario once again, maybe you can make another
suggestion? (Please :-})
I have a series of methods testFunction1(), testFunction2(), ..., which
sort of probe the limits of my program. They execute a loop which takes
longer each time. I want to know how many loops can be done in a fixed
time, say 2 minutes.
I want to do the following:
start testFunction1()
wait for 2 minutes, testFunction1 is running and eating CPU
cut off execution of testFunction1()
print some stats to standard out
start testFunction2()
and so on...
until all my testFunction()s are through, then stop.
Right now, it looks like this:
try {
testFunction1()
} catch (OutOfMemoryError e) {
System.gc();
System.out.println("OOME!");
}
try {
testFunction2()
} catch (OutOfMemoryError e) {
System.gc();
System.out.println("OOME!");
}
....
this works, since until recently, memory was the main problem in the
functions. However, I applied some nice tricks (hum), and now memory is
no longer the problem, but rather execution time. So something similar,
which, instead of waiting for an OOME, waits for X minutes, then breaks
off execution, and start the next one.
In short: it would be nice if I wouldn???t need the testing for the flag
(be it a volatile of Thread.isInterrupted()). Any ideas?
If it's CPU, probably a better idea is to poll a volatile flag.
import java.util.concurrent.atomic.AtomicBoolean;
public static void main(String[] args) {
final AtomicBoolean stop = new AtomicBoolean();
final Thread mainThread = Thread.currentThread();
Thread interrupter = new Thread(new Runnable() {
public void run() {
try {
Thread.sleep(120*1000);
stop = true;
} catch (java.lang.InterruptedException exc) {
// Just exit.
}
}
});
interrupter.setDaemon(true); // Shouldn't keep process alive.
interrupter.start(); // Important.
... do stuff ...
if (stop.get()) {
break;
}
...
// Let the interrupted exit, if hasn't already.
interrupter.interrupt();
}
You can, of course, use java.util.Timer or
java.util.concurrent.ScheduledThreadPoolExecutor instead of the
Thread+sleep.
I don???t really see how. It basically is the same, right? One would
need to write a TimerTask which sets the flag. Ok.
H.
- --
Hendrik Maryns
http://tcl.sfs.uni-tuebingen.de/~hendrik/
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