Date: Thu, 28 Oct 1999 15:57:52 -0400 From: "Daniel M. Eischen" <deischen@gdeb.com> To: julian@whistle.com Cc: marcel@scc.nl, jake@checker.org, freebsd-arch@freebsd.org Subject: Native threads (was Re: rfork patch, please comment) Message-ID: <3818AAC0.D5587B9E@gdeb.com>
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Julian Elischer wrote:
> I know I've been a fan of using rfork for native threads,
> (and all the support that we need for a linuxthreads is already there
> (see the linuxthread PORT to freebsd)). But I was speakin gwith terry the
> other day and he managed to convince me that there is an even better way
> that we could do this.
>
> It's really quite elegant.
Let's hear more. Especially if we can get efficient access to
thread-specific data.
I've been looking at various papers on threading, and was the most
impressed with the "Scheduler Activations: Effective Kernel Support
for the User Level Management of Parallelism".
The basic plan I had laid out was to:
1. Develop support for {get,set,make,swap}context.
2. Add a system call or two to allow the kernel to upcall
to a ucontext which would notify the threads library when
a process blocks/unblocks in the kernel. This would also
change the threads library and eliminate all the polling.
3. Add support for multiple [lightweight] processes to get
M by N threading. The basic problem here is how to get fast
access to thread-specific data (including a pointer to the
current thread).
I have working i386 support for 1. Marcel said he might be able
to help with the Alpha-bits. #2 doesn't seem that difficult, but
will involve changes to the wait queues that might be questioned.
My biggest concern with #3 was TSD. Inter [lightweight] process
locking doesn't seem _that_ difficult given that the threads library
does all the scheduling and is notified when a process blocks.
Dan Eischen
eischen@vigrid.com
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