Re: [RFC] New locking primitive for 2.5

yodaiken
2002-02-07T20:16:54Z

On Thu, Feb 07, 2002 at 03:08:02PM -0500, Robert Love wrote:
> On Thu, 2002-02-07 at 14:58, yodaiken@fsmlabs.com wrote:
>
> > On Thu, Feb 07, 2002 at 01:40:59PM -0500, Robert Love wrote:
> > > We shouldn't engage in wholesale changing of spinlocks to semaphores
> > > without a priority-inheritance mechanism. And _that_ is the bigger
> > > issue ...
> >
> > Cool. We can then have the Solaris "this usually doesn't fail on test" priority
> > inherit read/write lock. I can hardly wait.
>
> Or, we could do things right and not.

I'd love to hear how things could be done right here.
There seem to be 3 choices for reader writer locks
1. Do the right thing and say no to inheritance: and this
means no inheritance on mutexes either.
2. Use the Solaris - "sometimes kinda works" method.
3. Make readers/writer locks very slow and expensive e.g
a complete list of reader identities that with atomic insert/delete
and with check for uniqueness on insert! Not to mention the write
promotion, any interactions between the "favor writes" design it should
have and inheritance, links for a mutex inheriting lock to follow down
the complete tree of paths from the r/w lock ...

--
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Victor Yodaiken
Finite State Machine Labs: The RTLinux Company.
www.fsmlabs.com www.rtlinux.com