Thanks. This helped me alot.
Regards,
Behrang S.
On Wed, 15 Dec 2004 00:18:46 +0100, Leon Rosenberg <[EMAIL PROTECTED]> wrote:
> Ok, just in case it was more confusing then helping.
> Here is the (imho) safe solution (haven't tested it, but it should work
> fine):
> The isLock method is needed to ensure, that all threads have the same "lock"
> value. Volatile should guarantee it, but it's not supported on all vms. You
> should call the unlock method after you know, that the processing of the
> file is finished.
> Another problem, you could have, is to ensure, that the page where the link
> is placed is still valid. You can ensure it, by giving your call to the
> action a timestamp parameter and check whether it's still the proper
> timestamp for the file.
>
> Here the code (without timestamp):
>
> public class youraction ...{
>
> private volatile boolean lock;
>
> private void lock() throws AlreadyLockedException{
> if (lock)
> throw new AlreadyLockedException();
>
> lock = true;
> }
>
> private void unlock(){
> lock = false;
> }
>
> private synchronized boolean isLocked(){
> return lock;
> }
>
> private synchronized void updateXML() throws AlreadyLockedException{
> //double check needed, in case another thread was already
> //between first isLocked and updateXML call.
> if (isLocked())
> throw new AlreadyLockedException();
>
> lock();
> //.... generate the xml file.
> unlock();
>
> }
>
> public ActionForward execute(
> ActionMapping mapping,
> ActionForm af,
> HttpServletRequest req,
> HttpServletResponse res)
> throws Exception {
>
> //...
> if (isLocked())
> return mapping.findForward("noupdate");
> try{
> updateXML();
> return mapping.findForward("updatecomplete");
> }catch(AlreadyLockedException e){
> return mapping.findForward("noupdate");
> }
> }
>
> }
>
> > >
> > >
> > > > -----Original Message-----
> > > > From: Behrang Saeedzadeh [mailto:[EMAIL PROTECTED]
> > > > Sent: Tuesday, December 14, 2004 4:34 PM
> > > > To: [EMAIL PROTECTED]
> > > > Subject: Preventing concurrent execution of an Action
> > > >
> > > > Hi
> > > >
> > > > I've an action that creates an XML file on the server. It's executed
> > > > by clicking on a link. I don't want multiple instances of it to be
> > > > executed concurrently.
> > > >
> > > > Does an approach like the following work?
> > > >
> > > > public class UpdateXmlAction ...
> > > > {
> > > > private static final boolean locked;
> > > >
> > > > public void execute(...) {
> > > >
> > > > if (UpdateXmlAction.locked) {
> > > > return;
> > > > }
> > > >
> > > > Synchronized(UpdateXmlAction.class) {
> > > > locked = true;
> > > > updateXml();
> > > > locked = false;
> > > > }
> > > >
> > > > }
> > > > }
> > > >
> > > > Thanks in advance.
> > > >
> > > >
> > > > --
> > > >
> > > > Behrang Saeedzadeh
> > > > http://www.jroller.com/page/behrangsa
> > > >
> > > > ---------------------------------------------------------------------
> > > > To unsubscribe, e-mail: [EMAIL PROTECTED]
> > > > For additional commands, e-mail: [EMAIL PROTECTED]
> > > >
> > > >
> > >
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> >
> >
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>
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>
>
--
Behrang Saeedzadeh
http://www.jroller.com/page/behrangsa
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