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/signal.c b/signal.c
index ef64c64e..2bab8ad8 100644
--- a/signal.c
+++ b/signal.c
@@ -94,6 +94,8 @@ static void sig_handler(int sig)
     if (!in_interrupt && async_sig_enabled) {
       uw_simple_catch_begin;
       async_sig_enabled = 0;
+      if (gc_inprogress())
+        gc_cancel();
       if (funcall2(lambda, num_fast(sig), t))
         sig_deferred |= (1UL << sig);
       uw_unwind {