Re: GWT and concurrency

I appreciate that with JavaScript interpreters executing in one thread
there will never be any *true* concurrency. However it seems perfectly
possible for concurrency issues to arise with the way that
asynchronous callbacks are used A simple example is if I am
continuously checking the value of a variable x, and then incrementing
it:
while(!stop) {
int i = x;
x = i+1;
}

Once the event occurs, the handler prints the variable and sets a flag
that causes the incrementing to stop:
print(x);
stop = true;

The intended behavior might be that the final value of the counter is
printed. However if the event handler is invoked right after the
assignment 'int i = x', the value will be incremented one more time
after it is printed, which is a concurrency bug.

In such cases the synchronized keyword could have been used to define
pieces of code which must not be interrupted by other pieces of code
in such way. In plain Java the synchronized keyword provides an easy
way of dealing with such issues. The problem I described in my first
post is very similar to this in nature and I am lost as to what to do.

I hope this makes what I mean a bit clearer. Of course I am not
excluding the possibility that I just misunderstood somthing about how
the GWT/JavaScript eventing mechanism works.

Thanks,

Johannes

On Sep 17, 5:40 pm, Thomas Broyer <t.bro...@gmail.com> wrote:
> On Sep 17, 4:13 pm, Johannes Lehmann
>
> <johannes.lehma...@googlemail.com> wrote:
> > OK, that is basically what I assumed. This however seems to create
> > concurrency issues, which the synchronized keyword was designed to
> > address. Without any language support such as semaphores or mutexes
> > and without any guarantees regarding preemption, how could I solve a
> > problem such as the above?
>
> Excuse my ignorance about semaphores/mutexes/preemption details, but
> how can there be concurrency issues if things never execute
> concurrently? (and *your* code will never execute concurrently with
> *your* code)
>
> If you really want the gory details:http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapi...

--
You received this message because you are subscribed to the Google Groups "Google Web Toolkit" group.
To post to this group, send email to google-web-toolkit@googlegroups.com.
To unsubscribe from this group, send email to google-web-toolkit+unsubscribe@googlegroups.com.
For more options, visit this group at http://groups.google.com/group/google-web-toolkit?hl=en.