Unified optimistic and pessimistic concurrency control for a software transactional memory (STM) system

A non-transitory, machine readable medium including program code which, when executed by a machine, causes the machine to perform the operations of:

• in response to encountering an operation associated with a transactional write operation referencing a data element:
• acquiring ownership of a first field of a transaction record associated with the data element;
• and
• acquiring ownership of a second field of the transaction record after acquiring ownership of the first field of the transaction record, wherein:
• the first field of the transaction record includes a pessimistic field to hold a pessimistic concurrency control value and the second field of the transaction record includes an optimistic field to hold an optimistic concurrency control value;
• acquiring ownership of the pessimistic field of the transaction record includes executing a first instruction to determine if an ownership value held in the pessimistic field of the transaction record indicates the pessimistic field is not locked and to modify the pessimistic field to hold a pessimistic locked value in response to determining the ownership value indicates the pessimistic field is not locked;
• and
• acquiring ownership of the optimistic field of the transaction record after acquiring ownership of the pessimistic field of the transaction record comprises executing a store operation to store an optimistic locked value in the optimistic field.

A system comprising:

• a processor;
• and
• a memory having code stored therein that, in response to execution by the processor, causes the processor to:
• encounter an operation associated with a transactional memory access to a data element;
• and
• maintain a meta-data location associated with the data element in response to encountering the operation associated with the transactional memory access to the data element, wherein the meta-data location comprises a first field to hold an optimistic concurrency control value and a second field to hold a pessimistic concurrency control value, the pessimistic concurrency control value is to include a first pessimistic field to hold a bit vector to correspond to pending transactions and a second pessimistic field to indicate a lock type, wherein a pending writer transaction is to set a corresponding bit in the bit vector and the second pessimistic field to a pessimistic write lock value to acquire a write lock of the data element.

A system comprising:

• a processor;
• and
• a memory having code stored therein that, in response to execution by the processor, causes the processor to, in response to encounter an operation associated with a transactional write operation referencing a data element:
• acquire ownership of a first field of a transaction record associated with the data element wherein the first field of the transaction record includes a pessimistic field to hold a pessimistic concurrency control value;
• and
• acquire ownership of a second field of the transaction record after acquiring ownership of the first field of the transaction record, wherein the second field of the transaction record includes an optimistic field to hold an optimistic concurrency control value,
• wherein to acquire ownership of the pessimistic field of the transaction record includes to execute a first instruction to determine if an ownership value held in the pessimistic field of the transaction record indicates the pessimistic field is not locked and to modify the pessimistic field to hold a pessimistic locked value in response to determination that the ownership value indicates the pessimistic field is not locked, and
• wherein to acquire ownership of the optimistic field of the transaction record after acquiring ownership of the pessimistic field of the transaction record comprises to execute a store operation to store an optimistic locked value in the optimistic field.