[11] RFR(XS): 8198826: -XX:+VerifyStack fails with fatal error: ExceptionMark constructor expects no pending exceptions

[David Holmes]

On 2/03/2018 7:35 PM, David Holmes wrote:
> On 2/03/2018 7:15 PM, Tobias Hartmann wrote:
>> On 02.03.2018 03:11, David Holmes wrote:
>>> It's not the scalarized object I'm concerned about but other actions 
>>> that may happen after the
>>> allocation point and which would never have occurred if the 
>>> allocation threw OOME. But perhaps such
>>> actions are not possible under the definition of "safe" for this 
>>> transformation.
>>
>> It depends on what kind of other actions that would be but it's 
>> clearly possible that the user would
>> see an OOME at an "unexpected" location in the code. For example:
>>
>> MyObject o = new MyObject();
>> o.x = 42;
>> o.y = 43;
>> System.out.println(o.x);
>> myMethod(); // Deoptimize here for some reason
>> System.out.println(o.y);
>> return;
>>
>> C2 could scalarize 'o' because EA determined that it does not escape 
>> and we would then need to
>> re-allocate once we deoptimize at the myMethod() call (because we will 
>> continue execution in the
>> interpreter and 'o' is still live). If this re-allocation fails, the 
>> user would see the printed "42"
>> followed by an OOME which is kind of unexpected at that point.
>>
>> It's the same with VirtualMachineErrors or metaspace OOMEs during 
>> class loading (they might be
>> "unexpected" to the user as well). According to [1], OOMEs can 
>> basically be thrown at any point in
>> the program because "OutOfMemoryError may be thrown when an excessive 
>> amount of time is being spent
>> doing garbage collection and little memory is being freed" [1].
> 
> Hmmm to me that violates the precise exceptions requirement of the 
> language.

Nope Im wrong - OOME is allowed to occur as an asynchronous exception, 
not just synchronous. [JLS 11.1.3] So this is allowed for.

David

>>> But we should probably discuss this elsewhere.
>>
>> Yes, the discussion is independent of this patch. Feel free to follow 
>> up by email or chat.
>>
>> Can I assume you are okay with webrev.01?
> 
> Yes - thanks.
> 
> David
> 
>> Thanks,
>> Tobias
>>
>> [1] 
>> https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/memleaks002.html 
>>
>>