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

[Shafi Ahmad]

Hi,

 

Could you please review the fix for JDK-8170299: Debugger does not stop inside the low memory notifications code.

 

With the current implementation 'debugger does not stop inside the low memory *notifications* code' 

This is expected as the notification code is getting executed with the service thread, which is a hidden thread.

 

shafi at shafi-ahmad:~/Java/jdk8/jdk8u-dev$ jdb -Xmx32m MemoryWarningSystem

Initializing jdb ...

> stop at MemoryWarningSystem$1:25

Deferring breakpoint MemoryWarningSystem$1:25.

It will be set after the class is loaded.

> run

run MemoryWarningSystem

Set uncaught java.lang.Throwable

Set deferred uncaught java.lang.Throwable

> 

. . .

> quit

 

Breakpoint not hit.

 

With the attached webrev, jdb stop  at breakpoint inside notification code.

 

shshahma at slc12kkg:/scratch/shshahma/Java/jdk-dev$ jdb -Xmx128m MemoryWarningSystem

Initializing jdb ...

> stop at MemoryWarningSystem$1:25

Deferring breakpoint MemoryWarningSystem$1:25.

It will be set after the class is loaded.

> run

run MemoryWarningSystem

Set uncaught java.lang.Throwable

Set deferred uncaught java.lang.Throwable

> 

VM Started: Set deferred breakpoint MemoryWarningSystem$1:25

 

Breakpoint hit: "thread=Debugger", MemoryWarningSystem$1.memoryUsageLow(), line=25 bci=0

25            System.out.println("Memory usage low!!!");

 

Debugger[1] where

  [1] MemoryWarningSystem$1.memoryUsageLow (MemoryWarningSystem.java:25)

  [2] MemoryWarningSystem$2.handleNotification (MemoryWarningSystem.java:48)

  [3] javax.management.NotificationBroadcasterSupport.handleNotification (NotificationBroadcasterSupport.java:284)

  [4] javax.management.NotificationBroadcasterSupport$SendNotifJob.run (NotificationBroadcasterSupport.java:361)

  [5] java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1,135)

  [6] java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:635)

  [7] java.lang.Thread.run (Thread.java:844)

  [8] jdk.internal.misc.InnocuousThread.run (InnocuousThread.java:134)

Debugger[1] list

21    

22        MemoryWarningSystem mws = new MemoryWarningSystem();

23        mws.addListener(new MemoryWarningSystem.Listener() {

24          public void memoryUsageLow(long usedMemory, long maxMemory) {

25 =>         System.out.println("Memory usage low!!!");

26            double percentageUsed = ((double) usedMemory) / maxMemory;

27            System.out.println("percentageUsed = " + percentageUsed);

28            MemoryWarningSystem.setPercentageUsageThreshold(0.8);

29          }

30        });

Debugger[1] threads

Group system:

  (java.lang.ref.Reference$ReferenceHandler)0x362 Reference Handler running

  (java.lang.ref.Finalizer$FinalizerThread)0x361  Finalizer         cond. waiting

  (java.lang.Thread)0x360                         Signal Dispatcher running

Group main:

  (java.lang.Thread)0x1                           main              running

Group InnocuousThreadGroup:

  (jdk.internal.misc.InnocuousThread)0x35f        Common-Cleaner    cond. waiting

  (jdk.internal.misc.InnocuousThread)0x4f1        Debugger          running (at breakpoint)

Debugger[1] step

> Memory usage low!!!

 

Step completed: "thread=Debugger", MemoryWarningSystem$1.memoryUsageLow(), line=26 bci=8

26            double percentageUsed = ((double) usedMemory) / maxMemory;

 

Please see the newly created thread "  (jdk.internal.misc.InnocuousThread)0x4f1        Debugger          running (at breakpoint)".

 

In the change, the class 'MemoryImpl' is derived from class 'NotificationBroadcasterSupport' instead of class 'NotificationEmitterSupport' 

NotificationBroadcastSupport takes an Executor, in the constructor of MemoryImpl we are calling super() with an executor, which is a visible thread.

 

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.02/

 

Testing: jprt -testset core, rbt --test nsk.jvmti.testlist,nsk.jdi.testlist.

 

Regards,

Shafi
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