Did Java on Solaris once had a Fiber-like threads?

[David Holmes]

On 13/10/2019 6:03 am, Arkadiusz Gasiński wrote:
> Hi,
> 
> Thanks for clarifying. I got only your mail directly, but noticed in the 
> loom-dev digests that other replied as well, thanks!
> 
> One follow up question I have now is: do fibers actually employ the M:N 
> model? A week ago I would have said without any doubt that they do, but 
> I guess I've read too much about multithreading models recently and now 
> I'm confused.

I believe the current Fiber threading model is M:N in general, but at 
time a Fiber may have to be pinned to a specific thread.

David

> Thanks,
> Arek
> 
> 
> 
> On Wed, Oct 9, 2019 at 12:01 PM David Holmes <david.holmes at oracle.com 
> <mailto:david.holmes at oracle.com>> wrote:
> 
>     On 9/10/2019 6:51 pm, Arkadiusz Gasiński wrote:
>      > Hi,
>      >
>      > I recently found the "*JDK 1.1 for Solaris Developer's Guide*"
>     article (
>      >
>     https://docs.oracle.com/cd/E19455-01/806-3461/6jck06gqe/index.html),
>     which
>      > says, in the Many-to-Many Model section, that "*a program can
>     have as many
>      > threads as are appropriate without making the process too heavy or
>      > burdensome. In this model, a user-level threads library provides
>      > sophisticated scheduling of user-level threads above kernel
>     threads. The
>      > kernel needs to manage only the threads that are currently active. A
>      > many-to-many implementation at the user level reduces programming
>     effort as
>      > it lifts restrictions on the number of threads that can be
>     effectively used
>      > in an application.*"
>      >
>      > That's just the definition of the many-to-many model, but later
>     in the same
>      > section, it's written that "*The Java on Solaris operating
>     environment is
>      > the first many-to-many commercial implementation of Java on an MT
>     operating
>      > system*". If that's the case, it looks like there already was a
>     version of
>      > Java that had Fiber-like threads. Was it only some proprietary
>      > implementation just for Solaris? What happened to it?
>      >
>      > BTW, if I understand correctly, the current versions of
>     Open/Oracle JDK
>      > employ the one-to-one multithreading models, correct?
> 
>     Java post "Green Threads" employs a 1:1 model with operating system
>     threads. However Solaris also had a M:N model between user-level
>     threads
>     and kernel threads (LWPs). So Java was not actively using anything
>     fiber-like, just plain java.lang.Thread that mapped 1:1 to a Solaris UI
>     Thread but it could get some of the benefits that we're ascribing to
>     Fibers, when running on Solaris (with the appropriate configuration
>     options).
> 
>     https://docs.oracle.com/cd/E19455-01/806-5257/6je9h0349/index.html
> 
>     David
> 
>      > Thanks,
>      > Arek
>      >
>