Linus Torvalds <torvalds@transmeta.com> writes:

> 	if (!has_created_master_process) {
> 		new_me = clone(CLONE_VM | SIGCHLD);
> 		if (new_me > 0) {
> 			/* Original thread turns into master process */
> 			printf("I am the new master process, bow down before me!\n");
> 			has_created_master_process = 1;
> 			for (;;) {
> 				if (!waitpid(-1, NULL, 0))
> 					continue;
> 				if (errno == ENOCHLD)
> 					exit(0);
> 				.. we could do signal propagation here ..
> 			}
> 		}
> 		/* This child now takes over the role of the original thread */

A bit more complicated due to switching of stacks but that's basically
it.  With this clone model using n+1 threads is the only way to get
the semantics right.

> Also, please do notice that one fundamental part of the CLONE_THREAD logic
> never made it into a stable kernel: the shared signal handling. So while
> CLONE_THREAD allows for many pthread-like things (one common process ID
> shared by all threads, for example), the most fundamental part of it was
> not actually merged into the standard kernel because of stability concerns
> in late pre-2.4 test cycle.

Exactly.  This is holding off everything.  The way this is solved
(basically: the limitations imposed on the userland implementation)
will determine much of the implementation.

I've done already a great deal of the implementation when Linus first
put the code in the late 2.3 kernels.  If somebody finally would get
the signal handling stuff done (and a few more little things, some
Linus already agreed on) we could have a compliant pthread
implementation soon.

-- 
---------------.                          ,-.   1325 Chesapeake Terrace
Ulrich Drepper  \    ,-------------------'   \  Sunnyvale, CA 94089 USA
Red Hat          `--' drepper at redhat.com   `------------------------
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