Browse Prior Art Database

Concurrency Filter

IP.com Disclosure Number: IPCOM000121093D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 7 page(s) / 240K

Publishing Venue

IBM

Related People

Kolb, JF: AUTHOR [+2]

Abstract

There are many aspects to a locking mechanism that is used to control a given process or to control the access of data. They include lock states, compatibility matrices or rules, queueing, etc. Rather than describing a complete locking mechanism, only those characteristics which pertain to 'lock states' and 'compatibility matrices' are described and then only to the extent necessary to describe the general algorithms themselves.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 24% of the total text.

Concurrency Filter

      There are many aspects to a locking mechanism that is
used to control a given process or to control the access of data.
They include lock states, compatibility matrices or rules, queueing,
etc.  Rather than describing a complete locking mechanism, only those
characteristics which pertain to 'lock states' and 'compatibility
matrices' are described and then only to the extent necessary to
describe the general algorithms themselves.

      To illustrate the different lock states and compatibility rules
consider the following two sets of lock states and compatibility
matrices.

      The locking states provided by the MVS Global Resource
Mechanism are as follows.
STATE     DEFINITION
FREE      The unlocked state of the lock.  If the lock is in this
state any other requested state can be granted.
SHARED    The shared state of the lock.  This state allows multiple
users at this level.  This state can be granted if the lock is in the
free state or if the lock is in the shared state.
EXCLUSIVE The exclusive state of the lock.  One and only one user can
hold the lock in this state.  The exclusive state can only be granted
to a user if the lock is in the free state when this lock state
is requested.

      The compatibility matrix for the MVS Global Resource
Serialization Mechanism is illustrated in Table 1.

      CURRENT STATE OF THE LOCK
REQUESTED
 STATE         FREE           SHARED         EXCLUSIVE
SHARED         SHARED         SHARED         NOT GRANTED
EXCLUSIVE      EXCLUSIVE      NOT GRANTED    NOT GRANTED
Table 1.  GRS Compatibility Matrix

      The locking states provided by the Information Management
System IRLM mechanism has nine states.  The compatibility matrix is
illustrated in Table 2.

      CURRENT LOCK STATE
REQUESTED
 STATE         00   01   02   03   04   05   06   07   08
01             01   01   02   03   04   05   06   07   **
02             02   02   02   03   04   05   06   **   **
03             03   03   03   03   **   **   **   **   **
04             04   04   04   **   04   05   **   **   **
05             05   05   05   **   05   **   **   **   **
06             06   06   06   **   **   **   **   **   **
07             07   07   **   **   **   **   **   **   **
08             08   **   **   **   **   **   **   **   **
** = Not Granted
Table 2.  IMS Compatibility Matrix

      The compatibility matrices illustrate the variable number of
lock states and lock transformation rules.  To accommodate this
degree of variability an interpretive approach with pre-stored
compatibility matrices has been suggested.  With that type of
approach or...