[RFC][netx]: fix memory leak introduced by my previous changeset.

[Deepak Bhole]

* Denis Lila <dlila at redhat.com> [2011-05-02 17:09]:
> Hi.
> 
> I just realized that my previous changeset was not ideal.
> It created a new thread group object for every NetxPanel,
> but it only created any threads in that thread group if
> a thread group had not already been created for that panel.
> 
> This can result in creating unused ThreadGroups. That's
> not a problem by itself - the problem is that they're not
> garbage collected even if they're unused (because they're
> created with a non null parent, and the parent keeps track
> of them in an internal list). This is effectively a (very small)
> memory leak.
> 
> The patch to fix this is attached. It just replaces the
> concurrent map with synchronized statements.
> 
> Ok to push?
> 

Just a reminder that if you push this in HEAD, please do it in 1.1 as
well, since it contains the previous patch.

Thanks,
Deepak

> Regards,
> Denis.

> diff -r 6fe7281c17b7 ChangeLog
> --- a/ChangeLog	Mon May 02 14:33:32 2011 -0400
> +++ b/ChangeLog	Mon May 02 16:40:48 2011 -0400
> @@ -1,3 +1,13 @@
> +2011-05-02  Denis Lila  <dlila at redhat.com>
> +
> +	* netx/net/sourceforge/jnlp/NetxPanel.java:
> +	Add imports.
> +	(uKeyToTG): Change to HashMap.
> +	(TGMapMutex): New mutex to synchronize uKeyToTG.
> +	(getThreadGroup): Synchronize on TGMapMutex.
> +	(NetxPanel): Only create a new thread group if one doesn't already
> +	exist for the computed uKey.
> +
>  2011-05-02  Deepak Bhole <dbhole at redhat.com>
>  
>  	* plugin/icedteanp/java/sun/applet/PluginAppletViewer.java
> diff -r 6fe7281c17b7 netx/net/sourceforge/jnlp/NetxPanel.java
> --- a/netx/net/sourceforge/jnlp/NetxPanel.java	Mon May 02 14:33:32 2011 -0400
> +++ b/netx/net/sourceforge/jnlp/NetxPanel.java	Mon May 02 16:40:48 2011 -0400
> @@ -27,7 +27,9 @@
>  import net.sourceforge.jnlp.runtime.JNLPRuntime;
>  
>  import java.net.URL;
> +import java.util.HashMap;
>  import java.util.Hashtable;
> +import java.util.Map;
>  import java.util.concurrent.ConcurrentHashMap;
>  import java.util.concurrent.ConcurrentMap;
>  
> @@ -49,8 +51,9 @@
>  
>      // We use this so that we can create exactly one thread group
>      // for all panels with the same uKey.
> -    private static final ConcurrentMap<String, ThreadGroup> uKeyToTG =
> -        new ConcurrentHashMap<String, ThreadGroup>();
> +    private static final Map<String, ThreadGroup> uKeyToTG =
> +        new HashMap<String, ThreadGroup>();
> +    private static final Object TGMapMutex = new Object();
>  
>      // This map is actually a set (unfortunately there is no ConcurrentSet
>      // in java.util.concurrent). If KEY is in this map, then we know that
> @@ -95,8 +98,12 @@
>  
>          // when this was being done (incorrectly) in Launcher, the call was
>          // new AppThreadGroup(mainGroup, file.getTitle());
> -        ThreadGroup tg = new ThreadGroup(Launcher.mainGroup, this.documentURL.toString());
> -        uKeyToTG.putIfAbsent(this.uKey, tg);
> +        synchronized(TGMapMutex) {
> +            if (!uKeyToTG.containsKey(this.uKey)) {
> +                ThreadGroup tg = new ThreadGroup(Launcher.mainGroup, this.documentURL.toString());
> +                uKeyToTG.put(this.uKey, tg);
> +            }
> +        }
>      }
>  
>      // overloaded constructor, called when initialized via plugin
> @@ -210,7 +217,9 @@
>      }
>  
>      public ThreadGroup getThreadGroup() {
> -        return uKeyToTG.get(uKey);
> +        synchronized(TGMapMutex) {
> +            return uKeyToTG.get(uKey);
> +        }
>      }
>  
>      public void createNewAppContext() {