RFR 8150778: Reduce Throwable.getStackTrace() calls to the JVM

[Coleen Phillimore]

On 3/2/16 1:58 PM, Aleksey Shipilev wrote:
> Hi Coleen,
>
> On 03/02/2016 09:44 PM, Coleen Phillimore wrote:
>> Summary: replace JVM_GetStackTraceDepth and JVM_GetStackTraceElement,
>> with JVM_GetStackTraceElements that gets all the elements in the
>> StackTraceElement[]
>>
>> These improvements were found during the investigation for replacing
>> Throwable with the StackWalkAPI.   This change also adds iterator for
>> BacktraceBuilder to make changing format of backtrace easier.
>>
>> Tested with -testset core, RBT nightly hotspot nightly tests on all
>> platforms, and jck tests on linux x64.  Compatibility request is approved.
>>
>> open webrev at http://cr.openjdk.java.net/~coleenp/8150778_jdk/
>> open webrev at http://cr.openjdk.java.net/~coleenp/8150778_hotspot
>> bug link https://bugs.openjdk.java.net/browse/JDK-8150778
> Looks interesting!
>
> Is there an underlying reason why we can't return the pre-filled
> StackTraceElements[] array from the JVM_GetStackTraceElements to begin
> with? This will avoid leaking StackTraceElement constructor into
> standard library, *and* allows to make StackTraceElement fields final.
> Taking stuff back from the standard library is hard, if not impossible,
> so we better expose as little as possible.

We measured that it's faster to allocate the StackTraceElement array in 
Java and it seems cleaner to the Java guys.
It came from similar code we've been prototyping for StackFrameInfo.
>
> Other minor nits:
>
>   * Initializing fields to their default values is a code smell in Java:
>       private transient int depth = 0;

ok, not sure what "code smell" means but it doesn't have to be 
initialized like this.  It's set in the native code.
>
>   * Passing a null array to getStackTraceElement probably SEGVs? I don't
> see the null checks in native parts.

Yes, it would SEGV.  I'll add some checks for null and make sure it's an 
array of StackTraceElement.

Thanks,
Coleen
>
> Thanks,
> -Aleksey
>