RE: OS-implemented threads

["Will Fitzgerald" <fitzgerald@inetmi.com>]

I was first attracted to MzScheme because it provided a Scheme with
threading that worked on different platforms (it's the number one bulleted
featured item on the MzScheme page "Pre-emptive threads for all platforms.")

Naively, I thought this meant that a program using threads would work
essentially the same on all platforms. This turned out not to be the case,
and for this and other reasons, I abandoned the particular approach I was
taking on the project I was working on.

So, on the one hand, threading should be abandoned if you can't get it to
Work Right on all platforms. On the other hand, it seems like an important
feature set.

But I take it that only *OS* threads are going away?


> -----Original Message-----
> From: owner-plt-scheme@fast.cs.utah.edu
> [mailto:owner-plt-scheme@fast.cs.utah.edu]On Behalf Of Matthew Flatt
> Sent: Wednesday, June 13, 2001 1:20 PM
> To: plt-scheme@fast.cs.utah.edu
> Subject: OS-implemented threads
>
>
> Quoting Alexey Mahotkin:
> > Please try to compile it with --enable-osthreads.
>
> This forces a question that's been on my mind, and I've been meaning to
> take a survey.
>
> With the recent changes to MzScheme, I inspected at a lot more code
> than normal in a short time; and I saw lots and lots of bugs in the
> support for OS-implemented threads, mainly in terms of unprotected
> shared variables and structures.
>
> Meanwhile, there's a tricky signal--select race in Unix, which can't be
> solved in the same way as in single-threaded mode; I don't know how to
> fix it. And we have little hope of properly supporting generic pthreads
> (no way to pause threads for GC, I think) or LinuxThreads
> (semaphore-wait is not breakable).
>
> In short, MzScheme's support for OS-implemented threads has many
> problems. Considering the significant maintenance overhead and clutter
> required to support the mode, I wonder whether it's worthwhile.
>
> In theory, OS-implemented threads provide the benefit of parallelism on
> multiprocessor machines. In practice, that's where MzScheme would be
> most likely to crash. Given the problems and the relative lack of bug
> reports, I doubt that anyone uses it. Obviously I don't.
>
> So, does anyone actually use MzScheme with OS-implemented threads?
> Would anyone be seriously disappointed if we drop support for
> OS-implemented threads in version 200?
>
> (To be clear, we'll certainly make MzScheme work when embedded in a
> multi-threaded application, as long as MzScheme itself is called from
> only one OS-implemented thread.)
>
> Thanks,
> Matthew
>
>