- * Exit the current transaction context, abandoning any read/write
- * operations performed within it and removing the thread from any
- * tvar wait queues if it was waitin. Note that if nested transactions
- * are not fully supported then this may leave the enclosing
- * transaction contexts doomed to abort.
+ * Roll back the current transatcion context. NB: if this is a nested tx
+ * then we merge its read set into its parents. This is because a change
+ * to that read set could change whether or not the tx should abort.