State of Loom

[Magnus Ihse Bursie]

Hi Ron,

Thank you for a well-written presentation!

I just reacted to the following statement: "ThreadLocals work for 
virtual threads, as they do for the OS-backed threads, but as they might 
drastically increase memory footprint". Could you possibly elaborate a 
bit on why this would be?

What is "drastically" here? Do you mean that like "if you have a million 
threads, then you will have a million copies of the thread local data in 
question"? That sounds like a very obvious result of combining huge 
number of threads with thread local data. If you have a fantazillion 
number of threads, then of course you are going to need a fantazillion 
number of stack local variables, so reasonably you will also need a 
fantazillion number of thread local variables.

Or do you mean that Loom will consume significantly *more* memory than 
N*sizeof(ThreadLocal data) for N threads? If so, why is that?

/Magnus

On 2020-05-15 16:55, Ron Pressler wrote:
> Hello.
>
> I’ve posted a document describing the project’s goals and current progress:
>
>      http://cr.openjdk.java.net/~rpressler/loom/loom/sol1_part1.html
>
> It is accompanied by a new EA build, based on jdk-15+21.
>
>      http://jdk.java.net/loom/
>
> The new continuations algorithm is now switched on by default, so if you haven’t
> explicitly turned it on before, you may see some performance improvements.
> You can switch it off with -XX:-UseContinuationChunks.
>
> — Ron
>
>
>