Computer-implemented method, system and program product for establishing multiple read-only locks on a shared data object

• US 20060168585A1
• Filed: 01/25/2005
• Published: 07/27/2006
• Est. Priority Date: 01/25/2005
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Stoodley, Mark G., Grcevski, Nikola, Sundaresan, Vijay, Stoodley, Kevin A.
• Granted Patent: US 7,823,150 B2
• Time in Patent Office: Days
• US Class Current: 718/104
• CPC Class Codes: G06F 2209/523 Mode
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

Under the present invention, a locking primitive associated with a shared data object is automatically transformed to allow multiple read-only locks if certain conditions are met. To this extent, when a read-only lock on a shared data object is desired, a thread identifier of an object header lock word (hereinafter “lock word”) associated with the shared data object is examined to determine if a read-write lock on the shared data object already exists. If not, then the thread identifier is set to a predetermined value indicative of read-only locks, and a thread count in the lock word is incremented. If another thread attempts a read-only lock, the thread identifier will be examined for the predetermined value. If it is present, the thread count will be incremented again, and a second read-only lock will be simultaneously established.

Claims

1. A computer-implemented method for automatically transforming a locking primitive for a shared data object to permit multiple threads to simultaneously hold read-only locks, comprising:

performing a field access analysis for the shared data object to determine whether a predetermined set of conditions are met; and

automatically transforming the locking primitive for the shared data object to permit multiple threads to simultaneously hold a read-only lock on the shared data object if the set of predetermined conditions are met.

2. The computer-implemented method of claim 1, wherein the automatically transforming step comprises:

setting a thread identifier in a thread identifier field of a lock word associated with the shared data object to a predetermined value; and

incrementing a thread count in a thread count field of the lock work for each read-only lock simultaneously obtained on the shared data object, wherein a read-write lock on the shared data object is not permitted as long as a read-only lock exists.

3. The computer-implemented method of claim 1, wherein the method is carried out at compile time of program code associated with the shared data object.

4. The computer-implemented method of claim 1, wherein the predetermined set of conditions includes a lack of a write command to global data objects or global variables in a synchronized region of program code associated with locking the shared data object.

5. The computer-implemented method of claim 1, wherein the predetermined set of conditions includes a lack of nested locks in a synchronized region of program code associated with locking the shared data object.

6. The computer-implemented method of claim 1, wherein the predetermined set of conditions includes restriction of a read-only for a synchronized region of program code associated with locking the shared data object.

7. A computer-implemented method for establishing multiple read-only locks on a shared data object, comprising:

providing a lock word for a shared data object that includes a thread identifier field, a thread count field, flat lock contention field and a lock inflation field;

examining the thread identifier field to determine if a read-write lock currently exists on the shared data object pursuant to an attempt by a first thread to obtain a read-only lock on the shared data object; and

incrementing a thread count in the thread count field to establish a first read-only lock on the shared data object by the first thread if the read-write lock has not been established.

8. The computer-implemented method of claim 7, further comprising:

examining the thread identifier field to determine if the read-write lock currently exists on the shared data object pursuant to an attempt by a second thread to simultaneously obtain a second read-only lock on the shared data object; and

incrementing the thread count to simultaneously establish the second read-only lock if the read-write lock has not been established.

9. The computer-implemented method of claim 7, further comprising setting a thread identifier in the thread identifier field to a predetermined value indicative of read-only locks after the examining step.

10. The computer-implemented method of claim 9, wherein the predetermined value comprises zero.

11. The computer-implemented method of claim 7, further comprising setting an FLC bit in an FLC field of the lock word pursuant to an attempt by a third thread to establish the read-write lock on the shared data object.

12. The computer-implemented method of claim 7, further comprising:

decrementing the thread count pursuant to a release of the second read-only lock by the second thread; and

decrementing the thread count pursuant to a release of the first read-only lock by the first thread.

13. A computerized system for establishing multiple read-only locks on a shared data object, comprising:

an analysis system for examining a thread identifier in a thread identifier field of a lock word associated with the shared data object to determine if a read-write lock currently exists on the shared data object pursuant to an attempt by a first thread to obtain a read-only lock on the shared data object;

a count system for incrementing a thread count in a thread count field of the lock word to establish a first read-only lock on the shared data object by the first thread if the read-write lock has not been established; and

a thread identifier system for setting a thread identifier in the thread identifier field to a predetermined value indicative of read-only locks.

14. The computerized system of claim 13, wherein the analysis system further examines the thread identifier field to check for the predetermined value pursuant to an attempt by a second thread to simultaneously obtain a second read-only lock on the shared data object, and wherein the count system further increments the thread count to simultaneously establish the second read-only lock if the predetermined value is present.

15. The computerized system of claim 13, wherein the predetermined value comprises zero.

16. The computerized system of claim 13, further comprising an inflation system for setting an inflation bit in an inflation field of the lock word pursuant to an attempt by a third thread to establish the read-write lock on the shared data object.

17. The computerized system of claim 13, wherein the count system further decrements the thread count for each release of the second read-only lock and the first read-only lock.

18. A program product stored on a recordable medium for establishing multiple read-only locks on a shared data object, which when executed, comprises:

program code for examining a thread identifier in a thread identifier field of a lock word associated with the shared data object to determine if a read-write lock currently exists on the shared data object pursuant to an attempt by a first thread to obtain a read-only lock on the shared data object;

program code for incrementing a thread count in a thread count field of the lock word to establish a first read-only lock on the shared data object by the first thread if the read-write lock has not been established; and

program code for setting a thread identifier in the thread identifier field to a predetermined value indicative of read-only locks.

19. The program product of claim 18, wherein the program code for examining further examines the thread identifier field to check for the predetermined value pursuant to an attempt by a second thread to simultaneously obtain a second read-only lock on the shared data object, and wherein the program code for incrementing further increments the thread count to simultaneously establish the second read-only lock if the predetermined value is present.

20. The program product of claim 18, wherein the predetermined value comprises zero.

21. The program product of claim 18, further comprising program code for setting an inflation bit in an inflation field of the lock word pursuant to an attempt by a third thread to establish the read-write lock on the shared data object.

22. The program product of claim 20, further comprising program code for decrementing the thread count for each release of the second read-only lock and the first read-only lock.

23. A method for deploying an application for establishing multiple read-only locks on a shared data object, comprising:

providing a computer infrastructure being operable to;

examine a thread identifier in a thread identifier field of a lock word associated with the shared data object to determine if a read-write lock currently exists on the shared data object pursuant to an attempt by a first thread to obtain a read-only lock on the shared data object;

increment a thread count in a thread count field of the lock word to establish a first read-only lock on the shared data object by the first thread if the read-write lock has not been established; and

set a thread identifier in the thread identifier field to a predetermined value indicative of read-only locks.

24. The method of claim 23, wherein the computer infrastructure is further operable to examine the thread identifier field to check for the predetermined value pursuant to an attempt by a second thread to simultaneously obtain a second read-only lock on the shared data object, and further increment the thread count to simultaneously establish the second read-only lock if the predetermined value is present.

25. Computer software embodied in a propagated signal for establishing multiple read-only locks on a shared data object, the computer software comprising instructions to cause a computer system to perform the following functions:

examine a thread identifier in a thread identifier field of a lock word associated with the shared data object to determine if a read-write lock currently exists on the shared data object pursuant to an attempt by a first thread to obtain a read-only lock on the shared data object;

increment a thread count in a thread count field of the lock word to establish a first read-only lock on the shared data object by the first thread if the read-write lock has not been established; and

set a thread identifier in the thread identifier field to a predetermined value indicative of read-only locks.

26. The computer software of claim 25, wherein the instructions further cause the computer system to examine the thread identifier field to check for the predetermined value pursuant to an attempt by a second thread to simultaneously obtain a second read-only lock on the shared data object, and to further increment the thread count to simultaneously establish the second read-only lock if the predetermined value is present.