International Computers Limited

Nasser Siddiqi

Albert Stephen Hilditch

Colin Michael Thomson

Steve Robert Pettifer

A distributed data processing system has a deadlock detection mechanism for detecting a potential deadlock involving a cyclic chain of dependencies between transactions. The system also has a deadlock doublechecking mechanism for confirming that all the dependencies in the potential deadlock chain are co-existent. If deadlock is confirmed, action is taken to break the deadlock. The deadlock doublechecking mechanism operates by marking the dependencies in the cyclic chain with a unique existence number, and subsequently checking that the existence number of each dependency in the cyclic chain is unchanged. Marking the dependencies may be performed by propagating a probe message, containing a unique probe existence number, and associating this probe existence number with each dependency visited by said marker probe.

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Rusholme, United Kingdom

Nasser Siddiqi