Draft JEP Announcement: "Computed Constants"

[Remi Forax]

> From: "Brian Goetz" <brian.goetz at oracle.com>
> To: "Per-Ake Minborg" <per-ake.minborg at oracle.com>, "leyden-dev"
> <leyden-dev at openjdk.org>
> Sent: Thursday, July 27, 2023 7:50:09 PM
> Subject: Re: Draft JEP Announcement: "Computed Constants"

> One thing that may not be obvious about this work is that what it effectively
> does is provide a supported, public, specified means to expose the
> functionality that is now restricted to internal JDK use via `@Stable`. (So
> computed constants is-to @Stable as VarHandles are to Unsafe::{get,put}Xxx.)
Not exactly, computed constant is more like an AtomicReference (as said in the javadoc) than a VarHandle. 
For a computed constant stored in an instance field (of a non constant instance), you pay the indirection cost. 

Perhaps what is missing is a ComputedConstant that have a method get() that takes an instance as first parameter (like a VarHandle on an instance field does), so we can have one computed constant for all the instances, so no indirection once the code is optimized. 

Rémi 

> On 7/27/2023 11:52 AM, Per-Ake Minborg wrote:

>> Hi all,

>> Maurizio and I have drafted a JEP for computed constants, which are
>> immutable value holders that are initialized at most once. They offer
>> the performance and safety benefits of final fields while offering
>> greater flexibility as to the timing of initialization. In the
>> context of Leyden, they could be one basis for shifting computation
>> both forward and backward in time.

>> The draft is here: [ https://openjdk.org/jeps/8312611 |
>> https://openjdk.org/jeps/8312611 ]

>> Now that the Leyden repo is open, I’ll publish the prototype code to a
>> new branch there shortly.

>> Comments are welcome!

>> Best, Per
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