Patent ID: 6725370
Filing Date: 2004-04-20
Classification: H04L

Abstract:
A data sharing computer system, comprising: a first computer system; a second computer system; a shared data storing unit operably connected to the first and second computer systems; and an access control information storing unit; wherein(A) the shared data storing device includes a plurality of data storing areas, which divides a shared data accessed by the first computer system and the second computer system, and stores the divided shared data to the plurality of data storing areas; (B) the access control information storing device stores an access control information which indicates whether each data storing area of the shared data storing device is accessible or not accessible; (C) the first computer system includes a first service unit, a first data access unit operably connected to the shared data storing device, and a first mutual exclusion unit operably connected to the access control information storing unit; wherein (1) in response to the first service unit instructing the first data access unit and the first mutual exclusion unit to access an arbitrary data storing area, the first mutual exclusion unit obtains the access control information of the instructed data storing area, decides whether the instructed data storing area is accessible or not accessible, and changes the access control information associated with the instructed data storing area to not accessible if decided as accessible; (2) the first data access unit accesses the instructed data storing area after the first mutual exclusion unit decides that the instructed data storing area is accessible and before the first mutual exclusion unit changes the access control information to not accessible; and (3) the first mutual exclusion unit changes the access control information of the instructed data storing area to accessible after the first data access unit accesses the instructed data storing area; (D) the second computer system includes a second service unit, a second data access unit operably connected to the shared data storing device, and a second mutual exclusion unit operably connected to the access control information storing unit; wherein (4) in response to the second service unit instructing the second data access unit and the second mutual exclusion unit to access an arbitrary data storing area the second mutual exclusion unit obtains the access control information of the instructed data storing area, decides whether the instructed data storing area is accessible or not accessible, and changes the access control information associated with the instructed data storing area to not accessible if decided as accessible; (5) the second data access unit accesses the instructed data storing area after the second mutual exclusion unit decides that the instructed data storing area is accessible and before the second mutual exclusion unit changes the access control information to not accessible; and (6) the second mutual exclusion unit changes the access control information of the instructed data storing area to accessible after the second data access unit accesses the instructed data storing area.