Re: [Qemu-devel] getting rid of coroutine-gthread?

[Brad Smith <brad@comstyle.com>]

On Sat, Jan 12, 2013 at 12:08:47PM +0000, Peter Maydell wrote:
> On 12 January 2013 09:07, Brad Smith <brad@comstyle.com> wrote:
> > On Fri, Jan 11, 2013 at 07:24:35PM +0100, Andreas F?rber wrote:
> >> Am 11.01.2013 19:11, schrieb Paolo Bonzini:
> >> > as far as I know OpenBSD and Linux/ARM were the main users of
> >> > coroutine-gthread.  Do you think we could dump it and rely on
> >> > coroutine-sigaltstack only?
> >>
> >> No, I believe there is explicit code in configure to force the GThread
> >> implementation on Mac OS X.
> >
> > That is to skip over testing for the ucontext implementation. There was
> > a build issue with the sigaltstack implementation but it was fixed
> > relatively recently.
> 
> Yes. That configure skip code is actually broken because it skips the
> test for the ucontext implementation but doesn't actually set the
> coroutine_backend variable to anything, so we end up with (a)
> a confusing message to the user saying just "coroutine backend"
> rather than "coroutine backend foo" and (b) the gthreads backend
> more by luck than judgement. Easiest fix here is probably to
> replace the 'if darwin' check with an "#ifdef some-darwin-symbol
> #error" in the makecontext test program (and incidentally we could
> add a comment to the effect that at least some versions of MacOS
> provide makecontext but make getcontext always return ENOTSUP;
> I had to trawl the mailing list to find out why we did that :-))
> 
> Even if we don't drop gthreads, I think there's an argument to be
> made for having sigcontext be the next backend to try after
> ucontext.
 
The ucontext support in OS X has been marked as deprecated, that
seems to have popped up with 10.6. No idea if it has been removed
all together since then. It was made obsolete in POSIX.1-2001.

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