Gauche threads stuck on OpenBSD

[Timo Myyrä]

Hi,

I'm trying to make Gauche Scheme work on OpenBSD but I'm hitting a wall
debugging it. The problem is that thread tests get stuck.
Debugging the issue would indicate that the thread test causes threads to
suspend and sem_wait blocks forever.
Gauche uses internal copy of boehm-gc for option -DDONT_ADD_BYTE_AT_END.

Here's the original mail thread on Gauche mailing list:
https://sourceforge.net/p/gauche/mailman/message/34969290/

So steps to reproduce this issue:

1) download and extract Gauche from
http://prdownloads.sourceforge.net/gauche/Gauche-0.9.4.tgz
tar xzf Gauche-0.9.4.tgz
cd Gauche-0.9.4

2) apply GC patches from /usr/ports/devel/boehm-gc
for p in /usr/ports/devel/boehm-gc/patches
do
  patch < $p
done

3) add following patch to and run autoconf

$OpenBSD$
--- configure.ac.orig   Sun Jul 20 00:11:12 2014
+++ configure.ac        Thu Mar 24 20:26:10 2016
@@ -199,6 +199,13 @@ case $GAUCHE_THREAD_TYPE in
       THREADDLLIBS="-lpthread -lrt"
       GAUCHE_THREAD_TYPE=pthreads
       ;;
+    *-*-openbsd*)
+      AC_DEFINE(GC_OPENBSD_THREADS,1,[Define to use OpenBSD threads])
+      AC_DEFINE(_PTHREADS)
+      THREADLIBS="-lpthread"
+      THREADDLLIBS="-lpthread"
+      GAUCHE_THREAD_TYPE=pthreads
+      ;;
     *-*-solaris*)
       AC_DEFINE(GC_SOLARIS_THREADS,1,[Define to use Solaris threads])
       AC_DEFINE(GC_SOLARIS_PTHREADS,1,[Define to use Solaris pthreads])

4) add following diff to src/main.c
--- a/src/main.c
+++ b/src/main.c
@@ -289,6 +289,10 @@ static void sig_setup(void)
     sigdelset(&set, SIGUSR1); /* used by GC to stop the world */
     sigdelset(&set, SIGUSR2); /* used by GC to restart the world */
 #endif /*GC_FREEBSD_THREADS*/
+#if defined(GC_OPENBSD_THREADS)
+    sigdelset(&set, SIGXFSZ);
+    sigdelset(&set, SIGXCPU);
+#endif
     Scm_SetMasterSigmask(&set);
 }

5) run ./configure --enable-threads=pthreads && make

6) to run the thread test, add following to debug.scm and
run `./src/gosh -ftest ./debug.scm`
(use gauche.threads)
 (print
  (let ([a (atom 0)] [ts '()])
    (dotimes [n 30]
      (push! ts
             (thread-start! (make-thread
                             (^[] (dotimes [m 10]
                                    (atomic-update! a (pa$ + 1))))))))
    (for-each thread-join! ts)
    (atom-ref a)))

As seem from the mail thread, the issue seems to be that on OpenBSD the thread
test get stuck on sem_wait call on gc/pthread_stop_world.c:645 for some reason.
Anyone have idea what could be the cause and how to proceed debugging this?

Timo