Add flag to check if currently doing GC

src/refcount.c

@@ -26,19 +26,24 @@
         (atomic_fetch_sub_explicit(obj, 1, memory_order_relaxed))
 #    define lock_entry_mtx(obj)   (lock_mutex(&obj->weak_ref->mtx))
 #    define unlock_entry_mtx(obj) (unlock_mutex(&obj->weak_ref->mtx))
+#    define store_flag_maybe_atomic(obj, value) \
+        (atomic_store_explicit(obj, value, memory_order_relaxed))
 #else
-#    define lock_mutex(m)          true
-#    define unlock_mutex(m)        true
-#    define store_wr_count(obj, c) (*(obj) = (c))
-#    define inc_wr_count(obj)      ((*(obj))++)
-#    define dec_wr_count(obj)      ((*(obj))--)
-#    define lock_entry_mtx(obj)    true
-#    define unlock_entry_mtx(obj)  true
+#    define lock_mutex(m)                       true
+#    define unlock_mutex(m)                     true
+#    define store_wr_count(obj, c)              (*(obj) = (c))
+#    define inc_wr_count(obj)                   ((*(obj))++)
+#    define dec_wr_count(obj)                   ((*(obj))--)
+#    define lock_entry_mtx(obj)                 true
+#    define unlock_entry_mtx(obj)               true
+#    define store_flag_maybe_atomic(obj, value) (*(obj) = (value))
 #endif
 
 /**
  * Default context to use for functions that do not take a context. You must
  * initialize this before use.
+ *
+ * > The default value of this is NULL.
  */
 RefcountContext *refcount_default_context = NULL;
 
@@ -85,6 +90,7 @@ refcount_make_context(size_t entry_offset,
 
     ctx->static_objects = NULL;
     ctx->gc_roots = NULL;
+    ctx->doing_gc = false;
     return ctx;
 }
 
@@ -689,6 +695,7 @@ ptrdiff_t refcount_context_garbage_collect(RefcountContext *ctx) {
     if (!lock_mutex(&ctx->gr_mtx)) {
         return -1;
     }
+    store_flag_maybe_atomic(&ctx->doing_gc, true);
     ptrdiff_t total_cleared = 0;
     RefcountList *root = ctx->gc_roots;
     while (root) {
@@ -698,6 +705,7 @@ ptrdiff_t refcount_context_garbage_collect(RefcountContext *ctx) {
         }
         total_cleared += res;
     }
+    store_flag_maybe_atomic(&ctx->doing_gc, false);
     unlock_mutex(&ctx->gr_mtx);
     return total_cleared;
 }