From 4915f53c25a6a8e44bd6212d5af4c74aff8abe99 Mon Sep 17 00:00:00 2001
From: Yorick Hardy <yorickhardy@gmail.com>
Date: Fri, 3 Jan 2025 00:56:21 +0200
Subject: [PATCH] gc: create a context for terminated thread objects

The context ensures that parametrised objects, continuations
and exception handlers can still be traced but are no longer
root objects (after thread terminations) and can be GCd eventually.

Partial work towards addressing issue #534.
---
 gc.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/gc.c b/gc.c
index bdc9e0c8..558a4e07 100644
--- a/gc.c
+++ b/gc.c
@@ -2773,8 +2773,33 @@ int gc_heap_merge(gc_heap * hdest, gc_heap * hsrc)
  */
 void gc_merge_all_heaps(gc_thread_data * dest, gc_thread_data * src)
 {
-  gc_heap *hdest, *hsrc, *cur, *prev;
-  int heap_type, freed;
+  gc_heap *hdest, *hsrc;
+  int freed, heap_type, i;
+  pair_type *context = NULL;
+  vector_type *v = src->scm_thread_obj;
+
+  // The following objects are part of the thread context and should
+  // be stored on the primordial thread's heap. Make this explicit by
+  // including it in the thread object.
+  if (src->gc_num_args > 0) {
+    for (i=src->gc_num_args-1; i>=0; --i) {
+      context = gc_alloc_pair(dest, (src->gc_args)[i], context);
+    }
+  }
+  if (src->gc_cont != NULL && is_object_type(src->gc_cont)) {
+    context = gc_alloc_pair(dest, src->gc_cont, context);
+  }
+  if (src->exception_handler_stack != NULL) {
+    context = gc_alloc_pair(dest, src->exception_handler_stack, context);
+  }
+  if (src->param_objs != NULL) {
+    context = gc_alloc_pair(dest, src->param_objs, context);
+  }
+
+  if (context != NULL) {
+    gc_mark_black(context);
+    v->elements[8] = context;
+  }
 
   for (heap_type = 0; heap_type < NUM_HEAP_TYPES; heap_type++) {
     hdest = dest->heap->heap[heap_type];