New protocol for disabling exception suppression

David Holmes David.Holmes at
Sat Apr 2 19:28:52 PDT 2011

Rémi Forax said the following on 04/03/11 11:52:
> On 04/02/2011 03:21 AM, joe.darcy at wrote:
>> As part of the library support for the try-with-resources statement,
>> several API changes were made to Throwable including an addSuppressed
>> method to allow suppressed exceptions to be recorded. As previously
>> discussed on coin-dev [1], to support VM needs for reusable exception
>> objects, a protocol was devised to disable the suppression mechanism so
>> that a zero-length array would be returned from getSuppressed even if
>> addSuppressed was called with a valid argument. The mechanism was a bit
>> of a kludge, relying on an initial call to addSuppressed with a null
>> argument, and the design was called out as such. [2] I'm happy to report
>> the JSR 334 expert group has devised a more elegant protocol to disable
>> exception suppression: a new constructor is added to Throwable which
>> supports disabling suppression. The existing constructors of Throwable
>> always enable suppression and addSuppressed(null) now always throws a
>> NullPointerException. A few exception and error types in the platform
>> are allowed by behave as if their objects were created with suppression
>> disabled.
>> The fix was recently pushed [3] and will appear in a future JDK 7 build.
>> -Joe
>> [1]
>> [2]
>> [3]
> So the code of the VM was changed to call the constructor if it exists ?

No. The VM never calls a constructor it just allocates zeroed memory - 
which has the same affect as calling the new constructor.


> Rémi

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