Check for NULL fields in TYPEDDATA memsize functions (#15633)

Some TYPEDDATA objects allocate struct fields using the GC right after
they get created, and in that case the VM can try to perform a GC and join
a barrier if another ractor started one. If we're dumping the heap in another
ractor, this acquires a barrier and it will call the `rb_obj_memsize` function on this
object. We can't assume these struct fields are non-null. This also goes for C extensions,
which may cause problems with heap dumping from a ractor if their memsize functions aren't
coded correctly to check for NULL fields. Because dumping the heap from a ractor is likely a
rare scenario and it has only recently been introduced, we'll have to see how this works in
practice and if it causes bugs.

1 files changed, 10 insertions, 6 deletions

diff --git a/weakmap.c b/weakmap.c
index 2ebf7d204f..ecdd219f62 100644
--- a/weakmap.c
+++ b/weakmap.c
@@ -139,9 +139,11 @@ wmap_memsize(const void *ptr)
     const struct weakmap *w = ptr;
 
     size_t size = 0;
-    size += st_memsize(w->table);
-    /* The key and value of the table each take sizeof(VALUE) in size. */
-    size += st_table_size(w->table) * (2 * sizeof(VALUE));
+    if (w->table) {
+        size += st_memsize(w->table);
+        /* The key and value of the table each take sizeof(VALUE) in size. */
+        size += st_table_size(w->table) * (2 * sizeof(VALUE));
+    }
 
     return size;
 }
@@ -689,9 +691,11 @@ wkmap_memsize(const void *ptr)
     const struct weakkeymap *w = ptr;
 
     size_t size = 0;
-    size += st_memsize(w->table);
-    /* Each key of the table takes sizeof(VALUE) in size. */
-    size += st_table_size(w->table) * sizeof(VALUE);
+    if (w->table) {
+        size += st_memsize(w->table);
+        /* Each key of the table takes sizeof(VALUE) in size. */
+        size += st_table_size(w->table) * sizeof(VALUE);
+    }
 
     return size;
 }