Do you have a reference on G1 read barriers? I believe you, but I can't find any information about that from a Google search.
I don't immediately see why you'd need a read barrier for snapshot-at-the-beginning. You only need to trace references from gray objects to white objects that were deleted, which is a write.
I don't immediately see why you'd need a read barrier for snapshot-at-the-beginning. You only need to trace references from gray objects to white objects that were deleted, which is a write.