+
+int interrupt_thread(pid_t pid, lispobj function)
+{
+ union sigval sigval;
+ sigval.sival_int=function;
+
+ return sigqueue(pid, SIG_INTERRUPT_THREAD, sigval);
+}
+
+/* stopping the world is a two-stage process. From this thread we signal
+ * all the others with SIG_STOP_FOR_GC. The handler for this thread does
+ * the usual pseudo-atomic checks (we don't want to stop a thread while
+ * it's in the middle of allocation) then kills _itself_ with SIGSTOP.
+ * At any given time, countdown_to_gc should reflect the number of threads
+ * signalled but which haven't yet come to rest
+ */
+
+void gc_stop_the_world()
+{
+ /* stop all other threads by sending them SIG_STOP_FOR_GC */
+ struct thread *p,*th=arch_os_get_current_thread();
+ struct thread *tail=0;
+ int finished=0;
+ do {
+ get_spinlock(&all_threads_lock,th->pid);
+ if(tail!=all_threads) {
+ /* new threads always get consed onto the front of all_threads,
+ * and may be created by any thread that we haven't signalled
+ * yet or hasn't received our signal and stopped yet. So, check
+ * for them on each time around */
+ for(p=all_threads;p!=tail;p=p->next) {
+ if(p==th) continue;
+ countdown_to_gc++;
+ kill(p->pid,SIG_STOP_FOR_GC);
+ }
+ tail=all_threads;
+ } else {
+ finished=(countdown_to_gc==0);
+ }
+ release_spinlock(&all_threads_lock);
+ sched_yield();
+ } while(!finished);
+}
+
+void gc_start_the_world()
+{
+ struct thread *p,*th=arch_os_get_current_thread();
+ get_spinlock(&all_threads_lock,th->pid);
+ for(p=all_threads;p;p=p->next) {
+ if(p==th) continue;
+ kill(p->pid,SIGCONT);
+ }
+ release_spinlock(&all_threads_lock);
+}