RFR: JDK-8227831: Avoid using volatile for write-once, read-many class field

[Kazunori Ogata]

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 <shade at redhat.com> wrote on 2019/07/17 16:49:08:

> From: Aleksey Shipilev <shade at redhat.com>
> To: Kazunori Ogata <OGATAK at jp.ibm.com>, core-libs-dev at 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]