TimerTask, scheduleAtFixedRate doesn't work parallel

Thread view:

tkonrath - 13 Oct 2005 09:20 GMT

Hi.

I have a problem according to the TimerTask - functionality of Java
1.4.2.

I have two timer-tasks which I want to start at the same time each day
(e.g. at 1 a.m.) in my web-application. I configured both well. I used
the scheduleAtFixedRate method to from the Timer class, because I must
be sure that these tasks are not running during the day when a lot of
users are online. So using the method schedule is not possible for me.

I have recognized that the timer tasks are not running parallel. They
are called like step by step.

So may question is, why are they doing so? I have not found any
information about this behaviour in the Internet.

Is it possible to execute timer tasks parallel using
scheduleAtFixedRate or is it just impossible?

Thanks for any hints.
cu,
Tom

Reply to this Message

Thomas Weidenfeller - 13 Oct 2005 09:35 GMT

> I have recognized that the timer tasks are not running parallel. They
> are called like step by step.
>
> So may question is, why are they doing so? I have not found any
> information about this behaviour in the Internet.

Really? From the Timer API documentation (emphasis by me):

"Corresponding to each Timer object is a single background thread that
is used to execute all of the timer's tasks, *sequentially*."

In general, I would recommend to use the operating system specific
feature to schedule such tasks, and not re-inventing the wheel if not
absolutely necessary.

If you really want a Java solution, there is some scheduling frame work
out there which you could either use or study to build your own:

http://www.opensymphony.com/quartz/

/Thomas

Signature

The comp.lang.java.gui FAQ:
ftp://ftp.cs.uu.nl/pub/NEWS.ANSWERS/computer-lang/java/gui/faq
http://www.uni-giessen.de/faq/archiv/computer-lang.java.gui.faq/

Reply to this Message

tkonrath - 17 Oct 2005 09:06 GMT

Thanks for your answer and your "emphasis" of the Timer API
documentation. Somehow I haven't read this part of the documentation...

We don't want to use a scheduling frame work because the timer tasks
are just a very small part of our product and up to now it is no big
problem that they are processed sequentially.

But when it will be a real problem for us, we will might use the
scheduling frame work you mentioned or we will just use a own Timer for
each task as Tom Hawtin mentioned it below.

Thanks for your help,
Thomas

Reply to this Message

Thomas Hawtin - 13 Oct 2005 12:33 GMT

> I have recognized that the timer tasks are not running parallel. They
> are called like step by step.

> Is it possible to execute timer tasks parallel using
> scheduleAtFixedRate or is it just impossible?

There is one thread per Timer. So if you schedule multiple tasks with a
single timer, they will be executed one-by-one. The easy solution is to
use multiple timers. Alternatively, immediately the task is fired, pass
it off to a thread pool.

If you move to 5.0 (it has been out for a year already), then the
concurrency library offers more sophisticated features.

http://java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/ScheduledExecutorSe
rvice.html

If you are sticking to 1.4 for not, but will be upgrading to 5.0, there
is a backport of nearly all the java.util.concurrent API.

http://www.mathcs.emory.edu/dcl/util/backport-util-concurrent/

Tom Hawtin

Signature

Unemployed English Java programmer
http://jroller.com/page/tackline/

Reply to this Message

Roedy Green - 17 Oct 2005 11:45 GMT

>I have recognized that the timer tasks are not running parallel. They
>are called like step by step.

See http://mindprod.com/jgloss/timer.html

Signature

Canadian Mind Products, Roedy Green.
http://mindprod.com Again taking new Java programming contracts.

Reply to this Message

TimerTask, scheduleAtFixedRate doesn't work parallel

Free Magazines