US 5,161,227 A · Multilevel locking system and method

Abstract

A multi-processor computer system in which each processor is under the control of separate system software and access a common database. A two level lock management system is used to prevent data corruption due to unsychronized data access by the multiple processors. By this system, subsets of data in the database are assigned respectively different lock entities. Before a task running on one of the processors access data in the database it first requests permission to access the data in a given mode with reference to the appropriate lock entity. A first level lock manager handles these requests synchronously, using a simplified model of the locking system having shared and exclusive lock modes to either grant or deny the request. All requests are then forwarded to a second level lock manager which grants or denies the request based on a more robust model of the locking system and queues denied requests. The denied requests are granted, in turn, as the tasks which have been granted access finish processing data in the database.

Claims11

Dependent claims

In a computer system including means for executing a plurality of tasks in parallel and a shared resource which may be accessed by any of the plurality of tasks, wherein access to the shared resource is controlled by requests from the plurality of tasks for a mode of access from a set of predetermined modes of access, a method for managing the requests, said method comprising the steps of:

a) receiving, at a first level access manager directly accessible by all of said plurality of tasks, a request from one of said plurality of tasks for access to the shared resource in a given mode, wherein said given mode is one of said predetermined modes;
b) checking the received request for compatibility with a currently allowed mode of access to the shared resource;
c) sending a message to the one task granting or denying the request if the request is found to be respectively compatible or incompatible in step b);
and
d) sending a further request from the one task to a second level access manager to which the shared resource has been assigned and which is directly accessible only by selected ones of said plurality of tasks, for access in the given mode if the request is found to be incompatible at step b).

2 more elements

In a computer system which includes means for executing a plurality of tasks concurrently and a set of data values which may be accessed by any of the plurality of tasks, a control system for controlling access to said set of data values, said control system comprising:

first level access management means, coupled to receive, from each of said plurality of tasks, requests for permission to access said set of data values in one of a predetermined set of modes, wherein said first level access management means selectively allows ones of said received requests and indicates a permitted mode of access to the set of data values;
and
second level access management means, to which said set of data values is assigned and which is coupled to directly receive said requests only from selected ones of said plurality of tasks for recording the requests which were allowed by said first level access management means and for queuing ones of said requests which are not allowed by said first level access management means.

Dependencies are inferred from the claim text.

Multilevel locking system and method

Life of this patent

Multilevel locking system and method

Life of this patent

Abstract

Claims11