RFR: jsr166 jdk9 integration wave 2

[Doug Lea]

On 11/25/2015 03:05 AM, Peter Levart wrote:
> On 11/25/2015 01:59 AM, Martin Buchholz wrote:
>> On Tue, Nov 24, 2015 at 2:30 PM, Peter Levart <peter.levart at gmail.com
>> <mailto:peter.levart at gmail.com>> wrote:
>>     What do you think of exception cloning?
>> Making copies of java objects has historically been troublesome (e.g.
>> Cloneable).
>
> I was only thinking of Cloneable. Serialization is troublesome. If Throwable was
> retrofitted to implement Cloneable and have the following new static method:

I still think this would be a useful feature, assuming no hidden snags.
In addition to CompletableFuture, we might be able to use it instead of
emulating a variant of it in ForkJoinTask.getThrowableException.
There are probably other candidate uses elsewhere (although I can't
think of any offhand).

In the mean time though, I think using addSuppressed in
CompletableFuture.whenComplete is the best we can do, and
surely better than not doing it.

-Doug

>
>      /**
>       * {@link Object#clone() Clones} given {@code exception} and returns it's
> clone which
>       * shares all state with original exception (shallow clone) except for the
> possible list of already
>       * {@link #addSuppressed(Throwable) added} {@link #getSuppressed() suppressed}
>       * exceptions. The suppressed exception instances are not cloned, just the
>       * list containing them. Further {@link #addSuppressed(Throwable) additions}
>       * to the suppressed exceptions of the returned clone instance
>       * don't affect the suppressed exceptions of original exception and vice versa.
>       *
>       * @param exception the exception to clone.
>       * @param <T>       the type of exception
>       * @return shallow clone of given exception with suppressed exception
>       * list shallow-cloned
>       * @since 1.9
>       */
>      @SuppressWarnings("unchecked")
>      public static <T extends Throwable> T clone(T exception) {
>          try {
>              Throwable clone = (Throwable) exception.clone();
>              if (clone.suppressedExceptions != null &&
>                  clone.suppressedExceptions != SUPPRESSED_SENTINEL) {
>                  clone.suppressedExceptions = new
> ArrayList<>(clone.suppressedExceptions);
>              }
>              return (T) clone;
>          } catch (CloneNotSupportedException e) {
>              throw new InternalError(e);
>          }
>      }
>
>
> ...then would you prefer using it or would you nevertheless prefer swapping the
> roles of exceptions in whenComplete?
>
> Regards, Peter
>