Method and apparatus for serializing resource access requests in a multisystem complex

• US 5,805,900 A
• Filed: 09/26/1996
• Issued: 09/08/1998
• Est. Priority Date: 09/26/1996
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Fulkerson, Carroll Eugene Jr., North, Benjamin John, Kowalski, Mark Albert, Frey, Jeffrey Alan, Fagen, Scott Andrew
• Primary Examiner(s): Sheikh, Ayaz R.
• Assistant Examiner(s): PHAN, RAYMOND NGAN
• Application Number:
  US08/717,998
• Time in Patent Office: 712 Days
• Field of Search: 395/287, 395/288, 395/289, 395/290, 395/726, 395/727, 395/728, 395/731, 395/732, 395/856, 395/857, 395/858, 395/859, 395/862, 395/865, 395/876, 395/872, 395/875, 395/670, 395/608, 395/671, 395/672, 395/674, 395/675, 395/677, 395/200.42-200.47, 395/292
• US Class Current: 710/220
• CPC Class Codes: G06F 9/52 Program synchronisation; Mutual exclusion, e.g. by means of semaphores
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database

Abstract

A method and apparatus for serializing a request for access to a resource originating from a requester in a system of a multisystem complex. Each system of the complex maintains local contention data indicating contention between requesters on that system for access to the resource, as well as a local contention summary summarizing the local contention data. A global manager for managing contention between the systems uses the local contention summaries to determine the existence of global contention for the resource. In response to a request for access to the resource originating from a requester on a system, the system determines whether the request requires an update of the local contention summary for the system. If the request does not require an update of the local contention summary, the system processes the request in accordance with the local contention data for the system. If the request does require an update of the local contention summary, the system notifying the global manager of the update and processing the request in accordance with the response received from the global manager.

Claims

1. A method for serializing a request for access to a resource originating from a requester in a system of a multisystem complex, said complex having a global manager for managing contention between said systems for access to said resource, said method comprising the steps of:

(a) maintaining for each of said systems local contention data indicating contention between requesters on said system for access to said resource;

(b) maintaining for each of said systems a local contention summary summarizing said local contention data, said local contention summary being used by said global manager to determine whether there is global contention between said systems for said resource; and

(c) in response to a request for access to said resource originating from a requester on one of said systems, having said system perform the steps of;

(1) determining whether said request requires an update of the local contention summary for said system;

(2) if said request does not require an update of said local contention summary, processing said request in accordance with the local contention data for said system; and

(3) if said request requires an update of said local contention summary, notifying said global manager of said update and processing said request in accordance with a response received from said global manager.

2. The method of claim 1 wherein said response indicates whether there is global contention for said resource.

3. The method of claim 1 wherein said request is for a specified mode of access to said resource, said system determining that no update of said local contention summary comprising is required if there are currently any waiters on said system for the requested mode of access to said resource.

4. The method of claim 1 wherein said local contention data comprises, for each of said systems, a queue of entries representing requesters from that system for access to said resource.

5. The method of claim 1 wherein the local contention summary for each system indicates whether a requester from that system has current access to said resource.

6. The method of claim 1 wherein the local contention summary for each system indicates whether a requester from said system is awaiting access to said resource.

7. The method of claim 1 wherein the local contention summary for each system indicates when the earliest requester awaiting access to said resource requested access to said resource.

8. The method of claim 1 wherein the local contention summary for each system indicates when the earliest requester awaiting exclusive access to said resource requested access to said resource.

9. The method of claim 1 wherein the local contention summary for each system indicates when the earliest requester awaiting shared access to said resource requested access to said resource.

10. The method of claim 1 wherein said global manager maintains global contention data indicating contention between said systems for access to said resource, said global contention data being based upon the local contention summaries for each of said systems, said global manager, in response to receiving a notification of said update from said system, performing the steps of:

determining whether said update leaves said resource in global contention;

if said update does not leave said resource in global contention, transmitting a response to said requester indicating that said resource is not in global contention; and

if said update leaves said resource in global contention, transmitting a response to said requester indicating that said resource is in global contention.

11. The method of claim 1 wherein said system, in response to a request from said requester to release said resource, performs said steps (c)(1)-(c)(3) for said request to release said resource.

12. The method of claim 2 wherein said system commits said update and processes said request in accordance with said local contention data if said response indicates the absence of global contention for said resource.

13. The method of claim 2 wherein said system denies said request if said response indicates the presence of global contention.

14. The method of claim 13 wherein said system cancels said update if said update makes said requester an owner of said resource.

15. The method of claim 4 wherein each of said entries in said queue indicates whether the requester currently has access to said resource.

16. The method of claim 4 wherein each of said entries in said queue indicates whether the requester requested exclusive or shared access to said resource.

17. The method of claim 4 wherein each of said entries in said queue indicates when the requester requested access to said resource.

18. The method of claim 5 wherein the local contention summary for each system indicates whether said current access is exclusive or shared.

19. The method of claim 10 wherein said global manager updates said global contention data in accordance with said update of said local contention summary.

20. The method of claim 10 wherein the local contention summary for each system comprises a lock state that is set to exclusive if any requester on that system is requesting exclusive access to said resource.

21. The method of claim 19 wherein said global manager updates said global contention data to identify said system as a waiter for said resource if said update of said local contention summary identifies said system as an owner of said resource and said resource is in global contention.

22. The method of claim 20 wherein said resource is determined to be in global contention if two or more of said systems have requesters for access to said resource and the lock state of at least one of said two or more systems is set to exclusive.

23. The method of claim 11 wherein said global manager, in response to receiving a notification of an update from said system following a request to release said resource, performs the steps of:

determining whether said resource was previously in global contention;

if said resource was not previously in global contention, transmitting a response to said requester indicating that said resource is not in global contention; and

if said resource was previously in global contention, transmitting a response to said requester indicating that said resource is in global contention.

24. The method of claim 11 wherein said global manager, in response to receiving a notification of an update from said system following a request to release said resource, performs the steps of:

determining the system having an oldest waiter for access to said resource; and

notifying said system having said oldest waiter that said resource is available.

25. The method of claim 11 wherein said global manager, in response to receiving a notification of an update from said system following a request to release said resource, performs the steps of:

determining the system having an oldest waiter for access to said resource;

if said oldest waiter is awaiting exclusive access to said resource, notifying said system having said oldest waiter that said resource is available;

if said oldest waiter is awaiting shared access to said resource, determining whether any system has a waiter for exclusive access to said resource;

if no system has a waiter for exclusive access to said resource, notifying all of said systems with waiters for access to said resource that said resource is available;

if any system has a waiter for exclusive access to said resource, notifying all of said systems with waiters for access to said resource that are older than said waiter for exclusive access to said resource that said resource is available for waiters that are older than said waiter for exclusive access.

26. The method of claim 25 wherein each of said systems with waiters, upon being notified that said resource is available, notifies the waiters on said system that said resource is available.

27. The method of claim 25 wherein each of said systems with waiters that are older than said waiter for exclusive access, upon being notified that said resource is available for waiters that are older than said waiter for exclusive access, notifies the waiters on said system that are older than said waiter for exclusive access that said resource is available.

28. Apparatus for serializing a request for access to a resource originating from a requester in a system of a multisystem complex, said complex having a global manager for managing contention between said systems for access to said resource, said apparatus comprising, on at least one of said systems:

(a) means for maintaining local contention data indicating contention between requesters on said system for access to said resource;

(b) means for maintaining a local contention summary summarizing said local contention data, said local contention summary being used by said global manager to determine whether there is global contention between said systems for said resource;

(c) means responsive to a request for access to said resource originating from a requester on said system for determining whether said request requires an update of said local contention summary;

(d) means responsive to a determination that said request does not require an update of said local contention summary for processing said request in accordance with said local contention data; and

(e) means responsive to a determination that said request requires an update of said local contention summary for notifying said global manager of said update and processing said request in accordance with a response received from said global manager.