Date: Fri, 22 Jan 1999 08:30:21 -0600 From: "Richard Seaman, Jr." <dick@tar.com> To: "Russell L. Carter" <rcarter@pinyon.org> Cc: freebsd-current@FreeBSD.ORG Subject: Re: Using LinuxThreads Message-ID: <19990122083021.E5495@tar.com> In-Reply-To: <199901220239.TAA06788@psf.Pinyon.ORG>; from Russell L. Carter on Thu, Jan 21, 1999 at 07:39:28PM -0700 References: <199901220239.TAA06788@psf.Pinyon.ORG>
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On Thu, Jan 21, 1999 at 07:39:28PM -0700, Russell L. Carter wrote:
> dick@tar.com said:
> %libc_r could be modified so that is doesn't replace libc, but rather
> %is an addon, comparable to the kernel threaded libc case. But, it
> %would involve a bit of work.
>
> I thought so at first, but then I had to look at wait4 today and
> now I'm not so sure. At least some of libc_r is very closely
> tied to the uthread scheduler:
Sure it is. But, I don't see why that prevents the possibility of leaving
libc in place and having libc_r just be an add on (not that I'm advocating
this). Taking your example, in libc the syscall is implemented as _wait4,
and wait4 is a weak alias to _wait4. If you replaced _thread_sys_wait4
below with _wait4 instead, and put the resulting code in a library separate
from libc (eg. in a "new" libc_r) along with the uthread scheduling code
and the rest of the uthread pthread code, you could leave libc alone.
Then, when you linked with libc and libc_r together, the wait4 in libc_r
would override the weak aliased wait4 in libc. If you didn't link with
libc_r, you'd have your plain old wait4.
The bigger problem is that the uthread code needs "two layer" aliasing
in order to implement pthread cancellation.
> pid_t
> wait4(pid_t pid, int *istat, int options, struct rusage * rusage)
> {
> pid_t ret;
>
> /* Perform a non-blocking wait4 syscall: */
> while ((ret = _thread_sys_wait4(pid, istat, options | WNOHANG,
> rusage)) == 0 && (options & WNOHANG) == 0) {
> /* Reset the interrupted operation flag: */
> _thread_run->interrupted = 0;
>
> /* Schedule the next thread while this one waits: */
> _thread_kern_sched_state(PS_WAIT_WAIT, __FILE__, __LINE__);
>
> /* Check if this call was interrupted by a signal: */
> if (_thread_run->interrupted) {
> errno = EINTR;
> ret = -1;
> break;
> }
> }
> return (ret);
> }
> #endif
--
Richard Seamman, Jr. email: dick@tar.com
5182 N. Maple Lane phone: 414-367-5450
Chenequa WI 53058 fax: 414-367-5852
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