[10] RFR for JDK-8170299: Debugger does not stop inside the low memory notifications code

[mandy chung]

On 9/4/17 3:11 AM, Shafi Ahmad wrote:
>
>
> The method hasListeners() is referenced  inside MemoryImpl.java and 
> defined in  NotificationEmitterSupport.
>
> This method is not present in  NotificationBroadcasterSupport so I 
> added it to NotificationBroadcasterSupport.
>
> Jdk10 bug: https://bugs.openjdk.java.net/browse/JDK-8170299
>
> Webrev link: http://cr.openjdk.java.net/~shshahma/8170299/webrev.01/ 
> <http://cr.openjdk.java.net/%7Eshshahma/8170299/webrev.01/>
>
>
This patch adds a new public method in NotificationBroadcasterSupport.  
I think this fix wants to avoid adding this public method since this fix 
is intended to be backport.

MemoryImpl checks if there is any listener registered to avoid 
instantiating the notification object if no listener handles it.

Replacing the internal sun.management.NotificationEmitterSupport with 
NotificationBroadcasterSupport is a good change.  I suggest to file a 
RFE to consider adding hasListeners method as a separate issue.

171 static final class ThreadExecutor implements Executor {
172 public void execute(Runnable r) { new Thread(r).start(); }
173 }

This creates a new thread for each listener to handle each notification 
which is overkill.   You can create one system daemon thread to handle 
all notifications for all listeners.

For this fix, you could simply update NotificationEmitterSupport to 
create a system daemon thread to handle all notifications. 
NotificationEmitterSupport::sendNotification should also be updated to 
ignore the exception (currently it throws an exception).

Mandy


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