[RFC][plugin]: fix concurrency problems in PAV.java

[Andrew Su]

----- Original Message -----
> Hi.
> 
> I already replied to this e-mail, but I didn't get it,
> so I'm assuming there are others who didn't. The reply
> is here:
> http://mail.openjdk.java.net/pipermail/distro-pkg-dev/2011-April/013537.html
> 
> In it I gave reasons for why I think the attached patch
> is the correct way to do things.
> 
> Is it good to go?

Deepak is right, ConcurrentHashMap doesn't lock on retrieval of value.
So it is still possible that we could be trying to write and read at the same time.
I propose to wrap the calls to status.get(identifier) in a synchronized method (preferably synchronizing on the object being affected [status]). Similarly, you would need to change updateStatus to synchronize on status as well. This would get rid of the problem with read while writing.

-- snip --

Cheers,
  Andrew

> 
> Thank you,
> Denis.
> 
> ----- Original Message -----
> > * Denis Lila <dlila at redhat.com> [2011-04-12 12:21]:
> > > Hi.
> > >
> > > I found a few problems in PluginAppletViewer.java.
> > > We were modifying/reading from two static hash maps
> > > concurrently. The hash maps were "applets" and "status".
> > > status was only modified in a synchronized method,
> ...