Updated ARM Spec

[David Holmes]

Rémi Forax said the following on 08/23/10 20:23:
> Le 23/08/2010 12:09, David Holmes a écrit :
>> Rémi Forax said the following on 08/23/10 20:06:
>>> You can explicitly call setStackTrace() on a shared immutable 
>>> exception, hence there is a problem.
>>> addSupressedExceptions() will have the same issue.
>>
>> I stand corrected. The Java side of the code couldn't care less about 
>> the VM level backtrace - it just installs a Java array. :(
>>
>>> I think the fix is to:
>>> - silently discard the stack trace taken as argument of 
>>> setStackTrace() if the cause is 'null' (or not 'this')
>>> - silently don't register suppressed-exceptions if cause is 'null'
>>
>> I think the Java code should be able to recognize a Throwable instance 
>> that should not allow these things to be set, and simply ignore the 
>> request. However that is a change in the spec for setStackTrace.
> 
> Yes, setStackTrace() can 'not succeed'.
> And the way to recognize such Throwable instance is to check is the 
> field 'cause' is null.

Except if someone invokes setCause(null).

By the way, probing further, the non-OOME shared pre-allocated instances 
do not guard themselves against fillInStackTrace being invoked upon 
them. That is arguably an additional bug. I say arguably simply because 
in the circumstances under which those other exceptions are thrown, 
having a misleading stacktrace is probably the least of the 
application's worries.

David


>> Suppressed-exceptions could then be modelled like backtrace support - 
>> an optional facility generally used but ignored for the pre-allocated 
>> immutable instances.
> 
> Yes, and the spec must be also updated accordingly.
> 
>>
>> David
> 
> Rémi