[sgen] Move & document write barrier.

diff --git a/mono/sgen/sgen-gchandles.c b/mono/sgen/sgen-gchandles.c
index b18a65afa82ddb7c436bcc3b69553e71cce526dd..3fb721e39f9592366262ef468b1607d048d6d5b2 100644 (file)
--- a/mono/sgen/sgen-gchandles.c
+++ b/mono/sgen/sgen-gchandles.c
@@ -231,11 +231,14 @@ handle_data_grow (HandleData *handles, guint32 old_capacity)
        entries = g_malloc0 (new_bucket_size);
        if (handles->type == HANDLE_PINNED)
                sgen_register_root ((char *)entries, new_bucket_size, SGEN_DESCRIPTOR_NULL, ROOT_TYPE_PINNED, MONO_ROOT_SOURCE_GC_HANDLE, "pinned gc handles");
+       /* The zeroing of the newly allocated bucket must be complete before storing
+        * the new bucket pointer.
+        */
+       mono_memory_write_barrier ();
        if (InterlockedCompareExchangePointer ((volatile gpointer *)&handles->entries [new_bucket], entries, NULL) == NULL) {
                if (InterlockedCompareExchange ((volatile gint32 *)&handles->capacity, new_capacity, old_capacity) != old_capacity)
                        g_assert_not_reached ();
                handles->slot_hint = old_capacity;
-               mono_memory_write_barrier ();
                return;
        }
        /* Someone beat us to the allocation. */