Hi,
removing volatile aligns LangReflectAccess initialization with the
pattern used for other access objects: it's only initialized in the
static initializer of some class which we ensure is initialized, which
means any initialization race is guarded by the initialization of said
class - in this case j.l.r.Modifier.
Initialization of other access objects are not guarded by any
explicit synchronization, however, since similar load/store barriers
will be in effect by ensuring the class that constructs the object has
been initialized. So I think you could remove the explicit
synchronization.
I'm not sure why LangReflectAccess has not moved in with other
SharedSecrets. Perhaps this is just an artefact of having been around
for a long time, but maybe that'd cause some cyclic bootstrap
dependency. Either way it's nice to see it align to use the same
pattern.
Thanks!
/Claes
On 2019-07-17 10:00, Kazunori Ogata wrote:
Hi Aleskey,
Thank you for your comment.
I forgot to mention one thing. I verified that all accesses to
langReflectioAccess calls the accessor "langReflectAccess()". Since this
variable is modified once from null to non-null, I think the write in the
setter is guaranteed to be visible in the getter by putting the
synchronized block in langReflectAccess().
Should I put comments about this assumption? Actually, in JDK11 there are
some lines that do not call the getter, so backport needs to fix them,
too.
Regards,
Ogata
Aleksey Shipilev <sh...@redhat.com> wrote on 2019/07/17 16:49:08:
From: Aleksey Shipilev <sh...@redhat.com>
To: Kazunori Ogata <oga...@jp.ibm.com>, core-libs-dev@openjdk.java.net
Date: 2019/07/17 16:49
Subject: [EXTERNAL] Re: RFR: JDK-8227831: Avoid using volatile for
write-
once, read-many class field
On 7/17/19 8:48 AM, Kazunori Ogata wrote:
Webrev: http://cr.openjdk.java.net/~ogatak/8227831/webrev/
Note this is generally not safe: it introduces data race on
langReflectAccess field access. It has
to be proved that everything that implements LangReflectAccess interface
makes this data race
benign: e.g. all fields that are accessed via those implementation are
final, read once, etc. And
briefly looking at that, I am not sure it is the case for the actual
accessor generators.
I'd cautiously leave "volatile" here.
--
Thanks,
-Aleksey
[attachment "signature.asc" deleted by Kazunori Ogata/Japan/IBM]
