On Thu, 16 Feb 2023 15:01:34 GMT, Per Minborg <pminb...@openjdk.org> wrote:
>> I noticed when looking at the code that there was no real need to use a CHM
>> to perform the tracking of activation in an ordered fashion on
>> ForEachOrderedTask, but instead a VarHandle can be used, reducing
>> allocations and indirection.
>
> src/java.base/share/classes/java/util/stream/ForEachOps.java line 372:
>
>> 370: private Node<T> node;
>> 371:
>> 372: @SuppressWarnings("unused") private volatile
>> ForEachOrderedTask<S, T> next; // Only accessed through the NEXT VarHandle
>
> I think the variable can be declared without `volatile` as the operations on
> the `VarHandle` will determine the memory semantics used regardless? So, the
> `NEXT.set()` at L431 might also be replaced with `NEXT.setVolatile()`
@minborg Good point. Reference here:
"Access modes will override any memory ordering effects specified at the
declaration site of a variable. For example, a VarHandle accessing a field
using the get access mode will access the field as specified by its access mode
even if that field is declared volatile. When mixed access is performed extreme
care should be taken since the Java Memory Model may permit surprising results.
" -
https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/invoke/VarHandle.html
@minborg To clarify, I intended to do a plain write since safe publishing will
be done by `fork()`
-------------
PR: https://git.openjdk.org/jdk/pull/12320
