Cancel in-progress gc if handling async signal.

If a signal goes off in the middle of gc that is
routed to an async lambda handler, we should cancel
gc, so the handler finds the heap in a good state.
Of course, the handler must not return in this
case, or else the interrupted gc will try to resume.

* gc.c (inprogress): New static flag.
(gc): Increment and decrement inprogress variable.
Abort if re-entered.
(gc_inprogress): New function.
(unmark): Do not clear FREE flags, only REACHABLE.
(gc_cancel): New function.

* gc.h (gc_inprogress, gc_cancel): Declared.

* signal.c (sig_handler): In the async lambda
case, check for an in-progress gc and cancel it.

1 files changed, 2 insertions, 0 deletions

diff --git a/gc.h b/gc.h
index 2d6c5cde..ba065903 100644
--- a/gc.h
+++ b/gc.h
@@ -32,6 +32,7 @@ void protect(val *, ...);
 val make_obj(void);
 void gc(void);
 int gc_state(int);
+int gc_inprogress(void);
 void gc_mark(val);
 void gc_conservative_mark(val);
 void gc_mark_mem(val *low, val *high);
@@ -47,6 +48,7 @@ extern int full_gc;
 #endif
 
 void unmark(void);
+void gc_cancel(void);
 void gc_hint_func(val *);
 void gc_report_copies(val *pvar);
 void gc_free_all(void);