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Date: Sat, 21 Jun 2003 13:50:14 +0400 (MSD)
From: Igor Sysoev <is@rambler-co.ru>
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To: Julian Elischer <julian@elischer.org>
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cc: threads@freebsd.org
Subject: Re: Implementing TLS: step 1
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On Fri, 20 Jun 2003, Julian Elischer wrote:

> > We can implement such scheme on x86:
> > 
> > gs -> [ TP                 ] ---> [ TLS                    ]
> >       [ struct kse_mailbox ]  +-> [ struct kse_thr_mailbox ]
> >       [      .km_curthread ] -+
> > 
> > When UTS would switch to the next thread it should set thread's TLS:
> > 
> >      kse_mailbox.km_curthread = NULL;
> >      gs:[0] = next_thr_tls;
> >      kse_mailbox.km_curthread = next_kse_thr_mailbox;  
> 
> yes and the last line is atomic.. But remember having a NULL curhtread
> pointer stops upcalls but it is not the ONLY thing that stops upcalls..
> A flag TMF_NOUPCALLS (spelling?) in the mailbox will also inhibit any
> upcalls. 1:1 threads (BOUND) threads, (system scope threads?) set this
> bit, but they still can have a mailbox for other purposes. (e.g. setting
> mode flags and stuff).

So NULL curthread is the short term (in UTS only) and atomic method to
disable upcalls while KMF_NOUPCALL flag is the long term and non-atomic (we
can not atomically update bit masks in general) method ?


Igor Sysoev
http://sysoev.ru/en/