Shared data access serialization method and apparatus

Claim 2

The method of claim 1, further comprising the step of constructing a substantially similar copy of the primary data store in an alternate data store, the alternate data store also having access control information comprising lock blocks.

Claim 3

The method for controlling access of claim 1 or claim 2 in which said exclusive access control method comprises the steps of: A) generating a lock key associated with said first system; B) writing said lock key to one of the lock blocks associated with said shared resource element, and associated with said first system, on the primary data store; C) reading all lock blocks associated with said resource from the primary data store; D) applying a lock rule method to resolve ownership of said resource.

Claim 4

The method of claim 1, 2 or 3 in which said exclusive access control method further comprises the steps of: A) determining, by an excessive wait detection method that the wait by a waiting system for the shared resource element has been excessive; B) passing exclusive control of the resource to the waiting system by a lock-stealing method.

Claim 5

The method of claim 3 or 4 in which said lock rule method comprises the steps of: A) identifying said first system as owner of said shared resource element on the primary data store if all lock blocks associated with said resource, except those also associated with said first system, are zero; B) identifying said first system as not owner of said shared resource element on the primary data store if at least one lock block associated with said shared resource element, but not associated with said first system, is nonzero, and each of said nonzero lock blocks has a time-of-day value older than that of said first system; and having said first system wait for notice of ownership of said shared resource element; C) if lock rules (A) and (B) do not apply, identifying an indeterminate ownership situation; generating, by said first system, a new time-of-day value; updating with said new time-of-day value all lock blocks associated with said shared resource element and with said first system; reading all lock blocks associated with said shared resource element; determining which of said read lock blocks has an oldest time-of-day value; and informing a second system associated with the one of said read lock blocks with the oldest time-of-day value that said second system is now owner of said shared resource element.

Claim 6

The method of claim 4 or 5 in which the lock-stealing method comprises the steps of: A) writing the lock block associated with the primary data store, associated with a former resource owner to the secondary data store; B) zeroing the lock block associated with the former resource owner in the primary data store; C) determining which waiting system has been waiting the longest for the resource, and signalling said waiting system that it has exclusive control of the shared resource element.

Claim 7

The method of claim 1 or anyone of claims 2-6 further comprising the steps of: A) determining, by local error detection means, that the primary data store has a defective record; B) performing local error correction on the primary data store.

Claim 8

The method of claim 2 or anyone of claims 3-7 further comprising the steps of: A) determining, by global error detection means, that the primary data store is uncorrectably in error; B) substituting the alternate data store for said primary data store; C) dynamically creating a new alternate data store.

Claim 9

In a multi-system central electronic complex (CEC) comprising systems each having main storage, system resources, an operating system for managing said system resources, and shared data residing on external media, a serialization mechanism for controlling access to said shared data comprising: A) a primary data store comprising a shared resource element having shared data; B) within said primary data store, exclusive access means for a first system in said complex acquiring exclusive access to the shared resource element on the primary data store; C) a global control element within said primary data store.

Claim 10

The multi-system CEC of claim 9 further comprising an alternate date store substantially similar to the primary data store.

Claim 11

The multi-system CEC of claim 9 or 10 in which the exclusive access means comprises a lock block having a system-related lock key associated with each shared resource element on the primary data store, said lock key having a system sequence number field and a time-of-day value field, said fields associated with a particular system having zero values on the primary data store when the particular system does not require the shared resource element; and having nonzero values on the primary data store when the particular system acquires exclusive control of the shared resource element.

Claim 12

The multi-system CEC of claim 10 or 11, further comprising: A) detection means for determining that said first system is failed or temporarily stopped, and B) preemption means for a second system preempting said first system and passing to a waiting system exclusive access to the resource of said shared data when said first system is failed or temporarily stopped.

Claim 13

The multi-system CEC of claim 12 in which the detection means comprises a timer-driven routine for comparing the waiting system's wait time against an "excessive wait" interval.

Claim 14

The multi-system CEC of claim 12 or 13 in which the preemption means comprises a stealing mechanism by which said second system identifies a new controlling system to be given exclusive control over said resource, removes exclusive control over the resource from the first system by setting the first system's primary lock key to zero and storing its former primary lock key in its secondary lock key position, and signals the new controlling mechanism that it now has exclusive control of the resource.