Described is a distributed lock processing technique that may be used to coordinate access to globally accessed resource between endpoints using the connecting message fabric. Processors in a data storage system communicate using the message switch of the message fabric. Each processor is an endpoint within a data storage system. Each endpoint, prior to requesting a lock, dynamically determines a current lock owner of the lock to be requested in accordance with a determination of which endpoints are available as lock owners at the current time. The lock request is issued to the current lock owner with a requested time period used by the lock owner to determine an expiration time. The lock expires automatically at the expiration time even if the lock holder becomes unavailable. If the current lock owner becomes unavailable, a new lock owner is determined prior to the next request for that lock.

Methods and systems for process rollback in a shared memory parallel processor computing environment use priority values to control process rollback. Process classes are defined and each process class is allocated a base priority value. Each process run by the system is associated with one of the classes. In accordance with a first embodiment, process priorities determine which process is rolled back. In accordance with a second embodiment, collision counts and class pair priorities determine which process is rolled back. The methods and systems ensure that critical processes are granted at least a minimum allocation of processor time, while less critical processes are not completely starved. The functionality the system is thereby improved.

A method of classification of transaction address conflicts in a computer system for ensuring efficient ordering in a two-level snoopy cache architecture. The disclosure provides a method of classification and handling of address conflicts within a system to minimize the impact that address ordering places in a multiprocessor system with multiple memory control agents generating potentially conflicting addresses. A set of classification for each potential transaction conflict is provided against which decisions are provided which identifies the earliest point at which a subsequent transaction within the system may proceed to the same address identified by a previous transaction in the system. Classification of transactions are provided in several high level classes which define how such transactions within the system are handled based on the method disclosed.

A forwarding device compares a first address from a first coherent input/output (I/O) transaction with an address from at least one processor-issued transaction to determine if an address conflict exists. The forwarding device completes a first processor-issued transaction of the at least one processor-issued transaction if the address conflict exists and rejects the first coherent I/O transaction. The forwarding device holds remaining processor transactions of the at least one processor-issued transaction that have an address conflict with the first address of the first coherent I/O transaction. The forwarding device transmits the first coherent I/O transaction to an external I/O device, waits for the first coherent I/O transaction to return from the external I/O device, and completes the first coherent I/O transaction. The forwarding device releases the remaining processor transactions once the first coherent I/O transaction has been completed.