Re: Lazy, cached supplier: most performant mutex mechanism?

We spent quite some time on this, you can read all about it here:
https://docs.scala-lang.org/sips/improved-lazy-val-initialization.html

On Fri, 31 Jul 2020 at 20:02, Benjamin Manes via Concurrency-interest <
[email protected]> wrote:

> I believe double-checked locking, such as Martin's version in Guava
> Suppliers#memoize
> <https://github.com/google/guava/blob/master/guava/src/com/google/common/base/Suppliers.java#L124-L137>,
> is the best approach on the JVM for instance-level memoization.
>
> On Fri, Jul 31, 2020 at 10:42 AM Ghadi Shayban via Concurrency-interest <
> [email protected]> wrote:
>
>> This seems like it would be a common stdlib ask, but what is the most
>> performant way to protect the code inside a supplier from being
>> concurrently realized more than once? Contention would be rare, and the
>> losing threads need to wait on the value being computed by the winning
>> thread.
>>
>> The most straightforward thing to do is a synchronized block, but this
>> currently pins a carrier thread in Project Loom.
>>
>> The Supplier needs to keep track of:
>> 1) the thunk, if unrealized
>> 2) a value, if realized
>>
>> Golang's sync.Once does this [1] (CAS, fallback to mutex. Doesn't
>> remember value)
>> Clojure's lazy sequences use synchronized [2]
>>
>> Is there a better way to approach this on the JVM?
>>
>> Thanks!
>>
>> [1] https://golang.org/src/sync/once.go
>> [2]
>> https://github.com/clojure/clojure/blob/30a36cbe0ef936e57ddba238b7fa6d58ee1cbdce/src/jvm/clojure/lang/LazySeq.java#L39-L46
>>
>>
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-- 
Cheers,
√

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