libguile thread safety

[Chris Vine <chris@cvine.freeserve.co.uk>]

Hi,

I am having problems using libguile in a multi-threaded environment,
which boils down to the following small test case, which fails with a
segmentation fault with guile-2.0.9:

#include <libguile.h>
#include <pthread.h>

void *guile_wrapper (void *data) {
  scm_c_eval_string ("(display \"Hello\n\")");
  return NULL;
}

void *thread_func (void *data) {
  scm_with_guile (&guile_wrapper, NULL);
  return NULL;
}

int main () {
  pthread_t thread1;
  pthread_t thread2;

  pthread_create (&thread1, NULL, thread_func, NULL);
  pthread_create (&thread2, NULL, thread_func, NULL);

  pthread_join (thread1, NULL);
  pthread_join (thread2, NULL);
  return 0;
}

However, it prints "Hello" correctly if only one thread is started.
It seems that scm_with_guile() is not thread safe in the form used
above. However the following suggest that it should be:

http://www.gnu.org/software/guile/manual/html_node/Multi_002dThreading.html#Multi_002dThreading
http://www.gnu.org/software/guile/manual/html_node/Initialization.html#Initialization

I am clearly doing something wrong, which is probably obvious to
others. Can anyone help me with this?  Perhaps I have to serialize use
of scm_with_guile() notwithstanding what is said in the documentation,
but if so it will be disappointing for the use to which I was hoping to
put it.

Chris