garbage collect context (fiber) properly

include/mruby.h

@@ -74,6 +74,8 @@ struct mrb_context {
   int rsize;
   struct RProc **ensure;
   int esize;
+
+  struct RFiber *fib;
 };
 
 enum gc_state {

mrbgems/mruby-fiber/src/fiber.c

@@ -80,9 +80,9 @@ fiber_init(mrb_state *mrb, mrb_value self)
 
   f->cxt = (struct mrb_context*)mrb_malloc(mrb, sizeof(struct mrb_context));
   *f->cxt = mrb_context_zero;
+  c = f->cxt;
 
   /* initialize VM stack */
-  c = f->cxt;
   c->stbase = (mrb_value *)mrb_calloc(mrb, FIBER_STACK_INIT_SIZE, sizeof(mrb_value));
   c->stend = c->stbase + FIBER_STACK_INIT_SIZE;
   c->stack = c->stbase;
@@ -104,6 +104,8 @@ fiber_init(mrb_state *mrb, mrb_value self)
   ci[1] = ci[0];
   c->ci++;                      /* push dummy callinfo */
 
+  c->fib = f;
+
   return self;
 }
 

src/gc.c

@@ -412,7 +412,9 @@ mark_context(mrb_state *mrb, struct mrb_context *c)
     mrb_gc_mark(mrb, (struct RBasic*)ci->proc);
     mrb_gc_mark(mrb, (struct RBasic*)ci->target_class);
   }
-  if (c->prev) mark_context(mrb, c->prev);
+  if (c->prev && c->prev->fib) {
+    mrb_gc_mark(mrb, (struct RBasic*)c->prev->fib);
+  }
 }
 
 static void
@@ -472,7 +474,6 @@ gc_mark_children(mrb_state *mrb, struct RBasic *obj)
       struct mrb_context *c = ((struct RFiber*)obj)->cxt;
 
       mark_context(mrb, c);
-      ((struct RFiber*)obj)->cxt = NULL;
     }
     break;