Message_Queue_Header

The two cursors of the message ring, in bytes counted from the start of the channel's life: read_cursor is how much the reader has finished with and write_cursor how much the writer has committed. They only grow; the position in the ring is the cursor modulo data_size_in_bytes, and write_cursor - read_cursor is what is waiting. They sit in different cache lines. Get the record with get_message_queue_header.