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IMS/VS Data Sharing Enhancements (GHT Update Delay)

IP.com Disclosure Number: IPCOM000050902D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 15K

Publishing Venue

IBM

Related People

Murray, TE: AUTHOR [+2]

Abstract

This article describes a method and apparatus for operating a computing system to support sequential processing within a block level data sharing environment. The system includes (1) a resource lock manager (IRLM) having resource hash table (RHT) entries providing private-use flags on global locks hashing into corresponding global hash table (GHT) entries and (2) pass the buck (PTB) communications means for synchronizing the GHT entries in at least one other resource lock manager. The system is operated to detect the release of a last global lock on a resource hashing into a given GHT entry, and to delay the reset of the private use flag in the RHT entry corresponding to the given GHT entry until it is time to send a buck to the other resource lock manager.

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IMS/VS Data Sharing Enhancements (GHT Update Delay)

This article describes a method and apparatus for operating a computing system to support sequential processing within a block level data sharing environment. The system includes (1) a resource lock manager (IRLM) having resource hash table (RHT) entries providing private-use flags on global locks hashing into corresponding global hash table (GHT) entries and (2) pass the buck (PTB) communications means for synchronizing the GHT entries in at least one other resource lock manager. The system is operated to detect the release of a last global lock on a resource hashing into a given GHT entry, and to delay the reset of the private use flag in the RHT entry corresponding to the given GHT entry until it is time to send a buck to the other resource lock manager.

The IMS/VS Resource Lock Manager (IRLM) provides the locking functions required for block level data sharing in IMS/VS Version 1 Release 2. Two IRLMs, each resident in a different MVS, communicate with each other via the Advanced Communications Function for Virtual Telecommunications Access Method (ACF/VTAM), thus providing locking services for multiple IMS/VSs resident in either of the two MVSs.

The IRLM contains two sections of code which execute asynchronously. One section of code, called the 'Request Handler', processes the lock/unlock requests. The second section of code, called 'Pass the Buck (PTB)', executes periodically (initiated by elapse of a time interval). The PTB code uses VTAM to pass global lock information between the two IRLMs.

The Request Handler maintains a lock control block structure which includes a Resource Hash Table (RHT). Included in the RHT are 'private-use' bits. PTB maintains a Global Hash Table (GHT). There is a one to one correspondence between the RHT 'private-use' bits and the GHT entries. Locks are obtained on resource names. Associated with a resource name is a 'hash' value. The hash value uniquely identifies a GHT entry and hence an RHT 'private-use' bit.

The purpose of the GHT is to show which of the IRLMs currently have lock requests against resources which map into specific GHT entries. In cases where only one IRLM has 'interest' in a specific GHT entry and that interest is known to the other IRLM, the IRLM which has declared its interest may grant locks on other resources which map into this GHT entry without having to communicate with the other IRLM regarding these subsequent lock requests. Many locks are held for a short duration. Hence, at any instant it is normal to see GHT entries in which only one of the IRLMs has interest.

The initial lock request which sets a GHT interest bit must be delayed. This is due to the fact that the Request Handler is not permitted to access the GHT. The Request Handler must interact with PTB to set the interest bit in the GHT. This process consists of building a PTB request element, placing the element on a PTB work queue, and suspending the IMS/VS loc...