Multiprocessor system includes operating system for notifying only those cache managers who are holders of shared locks on a designated page by global lock manager

• US 5,226,143 A
• Filed: 03/14/1990
• Issued: 07/06/1993
• Est. Priority Date: 03/14/1990
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Myers, James J., Baird, Robert, Tetzlaff, William H., Bozman, Gerald P., Lett, Alexander S.
• Primary Examiner(s): Harrell, Robert B.
• Assistant Examiner(s): Geckil, Mehmet
• Application Number:
  US07/493,581
• Time in Patent Office: 1,210 Days
• Field of Search: 395/425, 395/250, 395/325, 395/425, 395/700, 395/650, 395/725, 364/134, 364/131, 364/138
• US Class Current: 711/145
• CPC Class Codes: G06F 12/0815 Cache consistency protocols

Abstract

A conditional broadcast or notification facility of a global lock manager is utilized to both serialize access to pages stored in local caches of counterpart processors in a distributed system and to ensure consistency among pages common to the caches. Exclusive use locks are obtained in advance of all write operations. When a page is to be updated, which page is cached in a processor other than that of the requester, then a delay is posed to the grant of the exclusive lock, all shared use lock holders to the same page notified, local copies are invalidated, exclusive lock granted, page is updated and written through cache, after which the lock is demoted to shared use.

Claims

1. A method for serializing access to and ensuring consistency among pages common to local caches in counterpart processors in a system having a shared external store, each processor having an operating system, internal store for programs and data pages, a local cache and cache manager, and means for executing programs located in said internal store and responsive to read and write instructions in said programs for causing the operating system to ascertain from said cache manager whether any pages designated in said read or right instructions are resident in said local cache, and in the absence thereof, for causing said operating system to access the shared external store and stage up to said local cache any copy of said designated pages resident in said shared external store, comprising the steps of:

(a) defining a lock manager by a predetermined one of the operating systems in a first processor over all resources in the system, said lock manager conditionally granting shared and exclusive locks, atomically changing its lock state, enqueuing requests for locks, notifying requesters of lock grant and all holders of a lock in conflict, said conditional granting being a grant or notification by said lock manager only to those cache managers of processors executing read or write instructions whose caches actually store or are in the process of staging up of pages designated by said instructions;

(b) responsive to each read instruction dispatched through the operating system of a requesting processor, obtaining a share lock on a designated page from the lock manager by the cache manager of the requesting processor, and either accessing the designated page in local cache of said requesting processor, or, copying said designated page into local cache of said requesting processor from the shared external store; and

(c) responsive to each write instruction dispatched through the operating system of the requesting processor, notifying only those cache managers of processors other than the requesting processor who are holders of share locks on the designated page by the lock manager, removing copies of the designated page from the notified local caches (cache invalidated), relinquishing any share locks, granting an exclusive lock on the designated page to the cache manager of the requesting processor, writing a changed or replacement page through the local cache of the requesting processor to the shared external store, and demoting the lock state of the cache manager of the requesting processor from exclusive to shared.

2. The method according to claim 1, wherein the atomic changing of lock state includes the changing of the state of a lock by a current lock holder without relinquishing the current lock state such as enqueing on a request.

3. The method according to claim 1, wherein said method further comprises the step of ascertaining priority among concurrent write instructions generated by programs among the processors according to an extrinsic logical locking convention.