[m-rev.] for review: don't terminate process until all threads done

[Julien Fischer]

On Mon, 30 Apr 2007, Peter Wang wrote:

> Branches: main
>
> Prevent multi-threaded programs from terminating as soon as the main thread
> terminates, i.e. the process should not terminate until all threads started by
> thread.spawn/3 terminate.

Is it worth having a predicate that lets the user disable it? 
I think there was a comment somewhere that indicated the reason this
hadn't been implemented was that a good default behaviour hadn't been
decided.  (I think this is a reasonable default behaviour.)

I think this is worth announcing in the NEWS file as well.

> This is done by maintaining a a global count of the number of threads started
> by thread.spawn.  In low-level C grades the main context will suspend if it
> reaches the global_success label and finds there are other contexts still
> outstanding.  The last context to terminate then reschedules the main context
> to resume.
>
> Similarly, in high-level C grades the main thread waits on a condition
> variable, which is signalled by the last thread to terminate.
>
> library/thread.m:
> runtime/mercury_context.c:
> runtime/mercury_thread.c:
> runtime/mercury_thread.h:
> runtime/mercury_wrapper.c:
> 	As above.
>
> 	Add some extra assertions related to this.
>
> tests/par_conj/Mmakefile:
> tests/par_conj/thread_barrier.exp:
> tests/par_conj/thread_barrier.m:
> 	Add test case

...

> only in patch2:
> unchanged:
> --- runtime/mercury_wrapper.c	17 Apr 2007 05:38:10 -0000	1.181
> +++ runtime/mercury_wrapper.c	30 Apr 2007 05:07:34 -0000
> @@ -2358,6 +2358,16 @@
>         }
>     }
>
> +  #if defined(MR_HIGHLEVEL_CODE) && defined(MR_THREAD_SAFE)
> +    assert(pthread_self() == MR_primordial_thread);

s/assert/MR_assert/

The rest looks okay (although it looks like part of your diff from the
other day got mixed up in it?).

Julien.
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