System for dynamically evaluating locks in a distributed data storage system

• US 6,917,942 B1
• Filed: 03/15/2000
• Issued: 07/12/2005
• Est. Priority Date: 03/15/2000
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Burns, Randal Chilton, Rees, Robert Michael
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): AL HASHEMI, SANA A
• Application Number:
  US09/526,155
• Time in Patent Office: 1,945 Days
• Field of Search: 707/8, 707/10, 707/9, 707/100, 707/201, 707/203, 707/200, 707/163
• US Class Current: 1/1
• CPC Class Codes: G06F 16/2343 Locking methods, e.g. distributed locking or locking implementation details

Abstract

A system and method for managing access to assets in a distributed data storage system includes requesting, from a client computer, a lock from a server computer. The lock is evaluated using a bitwise comparison of the protected access modes and restricted access modes defined by the lock with the protected and restricted modes defined by the currently outstanding locks using an algorithm, such that a potentially large compatibility table is not needed.

Claims

1. A computer system, comprising:

at least one general purpose server computer;

at least one general purpose client computer;

a distributed data storage system accessible to at least the client computer; and

logic executable by the client computer for undertaking method acts to evaluate lock requests in the storage system, the method acts comprising;

determining whether to grant a requested lock using at least one algorithm without using a lock compatibility table, the lock pertaining to at least one asset in the storage system.

2. The system of claim 1, wherein the determining act is undertaken by accessing a summary string of outstanding locks.

3. The system of claim 2, wherein the algorithm is based on respective sets of privileges granted by at least two locks, and on respective sets of sharing privileges restricted by the two locks.

4. The system of claim 3, wherein the summary string defines a first set P_S of protected access modes and a first set D_S of restricted access modes, and the requested lock defines a second set P_R of protected access modes and a second set D_R of restricted access modes, and the algorithm determines whether the intersection of at least one of:

the first set P_S of protected access modes and second set D_R of restricted access modes, and the second set P_R of protected access modes and first set D_S of restricted access modes.

5. The system of claim 4, wherein the requested lock is granted if (P_R∩

D_S=0)^(P_S∩

D_R=0).

6. The system of claim 4, wherein an upgrade lock is determined that is represented by a union of outstanding and requested protected modes and outstanding and requested restricted modes.

7. A computer system, comprising:

at least one general purpose server computer;

at least first and second general purpose client computers;

a distributed data storage system accessible to at least the client computers; and

logic executable by the server computer for undertaking method acts to manage access to assets in the storage system, the method acts comprising;

receiving a request for a first lock from the first client computer;

determining at least whether the first lock is compatible with at least a second lock associated with the second client computer based on a bitwise evaluation of respective first and second sets of access privileges and sharing privileges associated with the first and second locks;

granting the request if the first lock is compatible with the second lock;

otherwise

demanding the second lock.

8. The system of claim 7, wherein the determining act is undertaken by accessing a summary string of outstanding locks.

9. The system of claim 7, wherein the algorithm is based on respective sets of privileges granted by at least two locks, and on respective sets of sharing privileges restricted by the two locks.

10. The system of claim 8, wherein the first lock is a requested lock and the summary string defines a first set P_S of protected access modes and a first set D_S of restricted access modes, and the requested lock defines a second set P_R of protected access modes and a second set D_R of restricted access modes, and the algorithm determines whether the intersection of at least one of:

the first set P_S of protected access modes and second set D_R of restricted access modes, and the second set P_R of protected access modes and first set D_S of restricted access modes.

11. The system of claim 10, wherein the requested lock is granted if (P_R∩

D_S=0)^(P_S∩

D_R=0).

12. A computer program device comprising:

a computer program storage device readable by a client computer; and

a program on the program storage device and including instructions executable by the client computer for evaluating a request for a requested lock, the program comprising;

computer readable code means for determining whether to grant the requested lock without using a lock compatibility table, the requested lock pertaining to at least one asset in the storage system.

13. The device of claim 12, wherein the means for determining uses an algorithm based on respective sets of privileges granted by at least two locks, and on respective sets of sharing privileges restricted by the two locks.

14. The device of claim 13, wherein a summary string defines a first set P_S of protected access modes and a first set D_S of restricted access modes, and the requested lock defines a second set P_R of protected access modes and a second set D_R of restricted access modes, and the algorithm determines whether the intersection of at least one of:

the first set P_S of protected access modes and second set D_R of restricted access modes, and the second set P_R of protected access modes and first set D_S of restricted access modes.

15. The device of claim 14, wherein the requested lock is granted if (P_R∩

D_S=0)^(P_S∩

D_R=0).

16. A computer-implemented method for managing access among plural client computers to assets in a distributed data storage system associated with at least one server computer, comprising the acts of:

issuing locks to client computers, the locks being conditions precedent for the grant of a file lock to open a file, the locks being relinquished upon demand of the server computer when no associated file lock is invoked, the issuing act being based on at least one of;

first and second sets of access privileges pertaining to first and second locks, respectively, and first and second sets of sharing privileges restricted by the first and second locks, respectively.

17. The method of claim 16, further comprising the act of:

combining one or more of the sets in an equation, to undertake the issuing act.

18. The method of claim 17, wherein the equation determines compatibility if (P_R∩

D_S=0)^(P_S∩

D_R=0).