RFR (S) 8205608: Fix 'frames()' in ThreadReferenceImpl.c to prevent quadratic runtime behavior

[serguei.spitsyn at oracle.com]

Hi Ralf,


On 7/20/18 07:28, Schmelter, Ralf wrote:
> Hi Sergue,
>
> I’ve updated the webref: http://cr.openjdk.java.net/~simonis/webrevs/2018/8205608.v4/

The copyright year in ThreadReferenceImpl.c still has to be 2018, not 2008.

http://cr.openjdk.java.net/~simonis/webrevs/2018/8205608.v4/test/jdk/com/sun/jdi/Frames2Test.java.html

   72             if (newDepth == -1_000) {
   73                 // Pop some frames so there is room on the stack for the
   74                 // call (including println()).
   75                 notifyRecursionEnded();
   76             }

   I have a concern on potential issue mentioned in the comment above.
   Should a StackOverflowError be expected here?

   79         } catch (StackOverflowError e) {
   80             // Use negative depth to indicate the recursion has ended.
   81             return -1;
   82         }

   What is going to happen if the StackOverflowError was really caught 
above?
   If I understand it correctly, the notifyRecursionEnded() call will be 
missed then.
   This breakpoint will be missed as well:

   107         bpe = resumeTo("Frames2Targ", "notifyRecursionEnded", "()V");



> JVMTI_ERROR_OPAQUE_FRAME was never returned from GetFrameLocation(). If it would have, the old code would have removed all native methods from the call stack. The original JVMDI call did indeed return JVMDI_ERROR_OPAQUE_FRAME, so maybe it was a leftover from the JVMDI->JVMTI transition.

Agreed.

> I’ve tried to make the test more readable and added some comments to explain why it is done the way it is.

Thank you for the update!


Thanks,
Serguei

> Best regards,
> Ralf
>
>
>
>
> From: serguei.spitsyn at oracle.com [mailto:serguei.spitsyn at oracle.com]
> Sent: Mittwoch, 18. Juli 2018 22:57
> To: Chris Plummer <chris.plummer at oracle.com>; Schmelter, Ralf <ralf.schmelter at sap.com>; serviceability-dev at openjdk.java.net; Stuefe, Thomas <thomas.stuefe at sap.com>
> Subject: Re: RFR (S) 8205608: Fix 'frames()' in ThreadReferenceImpl.c to prevent quadratic runtime behavior
>
> Hi Ralf,
>
> The fix itself looks pretty good to me.
> Some minor comments.
>
> The copyright year needs an update.
>   218     jint count, filledIn;
>
>   Could you, please, split the declarations above into different lines to follow the local style?
> Ii is interesting that the original implementation checked the error code returned
> from the JVMTI GetFrameLocation for being equal to JVMTI_ERROR_OPAQUE_FRAME.
> However, the GetFrameLocation spec does not list this error code as possible.
>
>
> Some comments about the test.
>    52     static void callEnded() {
>    53         System.out.println("SOE occurred as expected");
>    54     }
>    55
>    56     static int call(int depth) {
>    57         if (depth == 0) {
>    58             // Should have seen a stack overflow by now.
>    59             System.out.println("Exited without creating SOE");
>    60             System.exit(0);
>    61         }
>    62
>    63         try {
>    64             int newDepth = call(depth - 1);
>    65
>    66             if (newDepth == -1_000) {
>    67                 // Pop some frames so there is room on the stack for the
>    68                 // println()
>    69                 callEnded();
>    70             }
>    71
>    72             return newDepth - 1;
>    73         } catch (StackOverflowError e) {
>    74             return -1;
>    75         }
>    76     }
>    77 }
>    I'd suggest to rename the methods call() and callEnded() to something like
>    recursiveMethod() and recursionEnd().
>    Also, the manipulations with SOE create a complexity and are confusing.
>    Could it be more simple to let it propagated and then catch in main()?
>    What is the point for all these checks at the lines 104-119?
>    In general, I'm looking for some ways to make it more clear, simple and stable.
>
> Thanks,
> Serguei