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From "Bill Stoddard" <b...@wstoddard.com>
Subject Re: [PATCH 2] worker MPM deadlock
Date Wed, 22 May 2002 18:58:10 GMT


> On Wed, May 22, 2002 at 01:59:02PM -0400, Cliff Woolley wrote:
> > On Wed, 22 May 2002, Aaron Bannert wrote:
> >
> > > The reason it's not implemented is because it's not guaranteed to do
> > > anything. Yielding is up to the discresion of the underlying system,
> > > and depending on many things it may behave differently. We can not
> > > get predictable scheduling with any variant of yield() in a way that
> > > will be portable. The only method we have right now for predictable
> > > scheduling in APR is apr_thread_cond.h.
> >
> > I'd say it's up to us to guarantee that it *does* do something on a
> > cross-platform basis.  That's APR's job.  If we're not going to do that,
> > then it needs to go away.  Having a function in the API that doesn't do
> > what it's supposed to do uniformly across platforms is bad karma.  It
> > works on Win32, why shouldn't it work on Unix?
>
> IIRC, this function exists so that netware and other
> single-multiplexed-process based thread libraries can have finer-grain
> control over execution sharing. The use case is a large computationally
> expensive function that hogs the CPU for a long time and can't yield the
> CPU since it hits none of the yieldable system calls. On systems that do
> true context switching between userspace threads, this doesn't need to be
> implemented. It in no way guarantees that the execution will be yielded,
> since that's up to the scheduling mechanism.
>
> -aaron
>

Aaron,
That is very disturbing but makes a lot of sense. Now I wonder if Sleep(0) on
WinNT -really- behaves as documented...

Bill


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