Question Regarding JEP 444: Virtual Threads and Use of ForkJoinPool

[David Holmes]

Hi,

On 14/06/2023 9:50 am, Bazlur Rahman wrote:
> Hello,
> 
> I was reading JEP 444, which discusses the implementation of Virtual 
> Threads. I've observed that the JDK's virtual thread scheduler employs a 
> work-stealing ForkJoinPool operating in FIFO mode, which is distinct 
> from the common pool operating in LIFO mode.
> 
> This has sparked my curiosity because ForkJoinPool, to my understanding, 
> has not traditionally been designed to handle I/O-bound tasks. However, 
> the design of virtual threads seems to be aimed precisely at addressing 
> such tasks.

Yes and it is the virtual threads mechanism that handles the I/O-bound 
tasks, not the underlying FJP. Where a regular thread in the FJP would 
block on an I/O operation and become unavailable for further use, it is 
the virtual thread that blocks, allowing the carrier thread in the FJP 
to continue executing other virtual threads.

Cheers,
David
-----

> Therefore, I'm curious as to why Java has opted to use the ForkJoinPool 
> for scheduling virtual threads. I would greatly appreciate it if you 
> could shed some light on what makes this design choice effective in 
> managing I/O-bound tasks, despite the ForkJoinPool's traditional usage 
> patterns.
> 
> Thank you for your time and consideration. I look forward to your 
> insights on this subject.
> *Thank you,*
> 
> *-*
> *A N M Bazlur Rahman*
> 
> ---
> /"And say: 'My Lord, increase me in knowledge.'" - Quran 20:114./
> 
> *Java Champion*
> *Software Engineer*
> JUG Leader, JUGBD.org 
> <https://mailtrack.io/trace/link/331a3fc3a3fa6407b1c1a71207d689d0bc35baca?url=http%3A%2F%2FJUGBD.org&userId=2428395&signature=31820ea85face89b>
> Java Queue Editor, InfoQ 
> <https://mailtrack.io/trace/link/4e67b5f2b63d9a192a80a28578b56f26ab3495b9?url=https%3A%2F%2Fwww.infoq.com%2Fprofile%2FA-N-M-Bazlur-Rahman%2F&userId=2428395&signature=0e89d13e753a8ce2>
> Editor at Foojay.io 
> <https://mailtrack.io/trace/link/ae78bc70831add10a5229ae14321984a51f052eb?url=https%3A%2F%2Ffoojay.io%2Ftoday%2Fauthor%2Fbazlur-rahman%2F&userId=2428395&signature=8a905c0967fa07c1>
> About Me 
> <https://mailtrack.io/trace/link/040f4646e384e62ba0900a14bc61657dbcec43b2?url=https%3A%2F%2Fbazlur.ca%2Fabout%2F&userId=2428395&signature=fc5823af331c641e>
> https://bazlur.ca/ 
> <https://mailtrack.io/trace/link/130dee54b46a76f0c11f910de05c700cdda0bb77?url=https%3A%2F%2Fbazlur.ca%2F&userId=2428395&signature=90ba6ea5871c4665>