RFR: JDK-8219412: Eager enum class initialization with enum switch

Liam Miller-Cushon cushon at google.com
Thu Apr 4 18:20:00 UTC 2019

Hi Jan,

There are a couple of other bugs about enum switch / class initialization
issues that I think are addressed by this approach:

Do you have a sense of how many additional auxiliary classes this will
create for typical applications? I'm wondering if the number of additional
classes might be large enough to effect performance (i.e. binary size,

Were other lazy initialization patterns considered? JDK-7176515 mentions
that ecj avoids this by caching the switch map in a field in the same class
as the switch.

On Thu, Apr 4, 2019 at 11:04 AM Jan Lahoda <jan.lahoda at oracle.com> wrote:

> Hi,
> When there is a switch over enum in the code, and is compiled into the
> bytecode, the meaning of the switch should not change even if the enum's
> constant are reordered. This is achieved by a map that maps the
> (current) enum constants to the appropriate case in the switch. This map
> is stored in a field in an auxiliary class, and filled when that
> auxiliary class is loaded in.
> But, if there are multiple switches over distinct enums under a single
> top-level class, the mapping fields for all the enums are stored in a
> single class. So, when any of these is needed, the mapping is
> constructed for all the enums, which may cause enum class initialization
> even in cases where it shouldn't happen.
> The proposed fix is to create a separate auxiliary classes for each
> enum/mapping.
> Proposed patch: http://cr.openjdk.java.net/~jlahoda/8219412/webrev.00/
> JBS: https://bugs.openjdk.java.net/browse/JDK-8219412
> How does this look?
> Thanks,
>      Jan
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