Clean up active exception handlers when garbage collecting a thread

Author: niner

src/core/threadcontext.c

@@ -82,6 +82,14 @@ MVMThreadContext * MVM_tc_create(MVMThreadContext *parent, MVMInstance *instance
 void MVM_tc_destroy(MVMThreadContext *tc) {
     MVMint32 i;
 
+    /* If an exception handler calls nqp::exit, we don't unwind the stack and
+     * exception handlers aren't cleaned up yet */
+    while (tc->active_handlers) {
+        MVMActiveHandler *ah = tc->active_handlers;
+        tc->active_handlers = ah->next_handler;
+        MVM_free(ah);
+    }
+
     /* Free the native callback cache. Needs the fixed size allocator. */
     /* (currently not. but might if MVMStrHash moves internally to the FSA.) */
     MVM_str_hash_demolish(tc, &tc->native_callback_cache);