Systems and methods for safely subscribing to locks using hardware extensions

Abstract

Transactional Lock Elision allows hardware transactions to execute unmodified critical sections protected by the same lock concurrently, by subscribing to the lock and verifying that it is available before committing the transaction. A 'lazy subscription' optimization, which delays lock subscription, can potentially cause behavior that cannot occur when the critical sections are executed under the lock. Hardware extensions may provide mechanisms to ensure that lazy subscriptions are safe (e.g., that they result in correct behavior). Prior to executing a critical section transactionally, its lock and subscription code may be identified (e.g., by writing their locations to special registers). Prior to committing the transaction, the thread executing the critical section may verify that the correct lock was correctly subscribed to. If not, or if locations identified by the special registers have been modified, the transaction may be aborted. Nested critical sections associated with different lock types may invoke different subscription code.