On Apr 9, 2013, at 9:30 AM, Zhong Yu <zhong.j...@gmail.com> wrote:
>
>
>
> On Mon, Apr 8, 2013 at 6:54 PM, Steven Schlansker
> <stevenschlans...@gmail.com> wrote:
> Today I encountered "java.lang.IllegalArgumentException: Self-suppression not
> permitted" from Throwable.addSuppressed.
>
> My first surprise is that the try-with-resources block can throw this
> exception; it is very confusing to have auto-generated code throw exceptions.
> But beyond that, it is impossible to figure out *which* exception caused the
> problem. If you have multiple resources acquired in the try-with-resources,
> it could be any of them.
>
> Would it be reasonable to change
>
> public final synchronized void addSuppressed(Throwable exception) {
> if (exception == this)
> throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
>
> to
>
> public final synchronized void addSuppressed(Throwable exception) {
> if (exception == this)
> throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE,
> this);
>
> so that when you get this exception it at least points to one of the throw
> sites that actually caused the problem? Otherwise the only stack trace you
> have is in auto-generated code and you are left scratching your head,
> wondering where it came from. I believe this would increase the
> debuggability of the try-with-resources construct and there's no immediately
> obvious downside.
>
> I'm not the only one who was confused by this behavior:
> http://stackoverflow.com/questions/12103126/what-on-earth-is-self-suppression-not-permitted-and-why-is-javac-generating-co
>
>
> Reusing exception is probably not a good idea - unless the exception is
> immutable, i.e. enableSuppression=writableStackTrace=true.
>
I agree, but there is (library) code out there that does this -- the code that
caused the problem wasn't even mine. My suggestion has no cost unless you
happen to trigger it, and then it helps you find who is causing trouble.
> Interestingly, even for an immutable exception, `e.addSuppressed(e)` isn't
> allowed. I think that it should be allowed.
>
> Zhong Yu
