OPPORTUNISTIC USE OF LOCK MECHANISM TO REDUCE WAITING TIME OF THREADS TO ACCESS A SHARED RESOURCE

• US 20110161539A1
• Filed: 12/31/2009
• Published: 06/30/2011
• Est. Priority Date: 12/31/2009
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Anand, Vaijayanthimala K., Olszewski, Bret R., Michel, Dirk, Hepkin, David A.
• Granted Patent: US 8,607,239 B2
• Time in Patent Office: Days
• US Class Current: 710/200
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

Embodiments of the invention provide a method, apparatus and computer program product for enabling a thread to acquire a lock associated with a shared resource, when a locking mechanism is used therewith, wherein each embodiment reduces waiting time and enhances efficiency in using the shared resource. One embodiment is associated with a plurality of processors, which includes two or more processors that each provides a specified thread to access a shared resource. The shared resource can only be accessed by one thread at a given time, a locking mechanism enables a first one of the specified threads to access the shared resource while each of the other specified threads is retained in a waiting queue, and a second one of the specified threads occupies a position of highest priority in the queue. The method includes the step of identifying a time period between a time when the first specified thread releases access to the shared resource, and a later time when the second specified thread becomes enabled to access the shared resource. Responsive to an additional thread that is not one of the specified threads being provided by a processor to access the shared resource during the identified time period, it is determined whether a first prespecified criterion pertaining to the specified threads retained in the queue has been met. Responsive to the first criterion being met, the method determines whether a second prespecified criterion has been met, wherein the second criterion is that the number of specified threads in the queue has not decreased since a specified prior time. Responsive to the second criterion being met, the method then decides whether to enable the additional thread to access the shared resource before the second specified thread accesses the resource.

Claims

1. In association with a plurality of processors including two or more processors that each provides a specified thread to access a shared resource, wherein the shared resource can only be accessed by one thread at a given time, a locking mechanism enables a first one of the specified threads to access the shared resource while each of the other specified threads is retained in a waiting queue, and a second one of the specified threads occupies a position of highest priority in the queue, a method comprising the steps of:

identifying a time period between a time when the first specified thread releases access to the shared resource, and a later time when the second specified thread becomes enabled to access the shared resource;

responsive to an additional thread that is not one of the specified threads being provided by a processor to access the shared resource during the identified time period, determining whether a first prespecified criterion pertaining to the specified threads retained in said queue has been met;

responsive to said first criterion being met, determining whether a second prespecified criterion has been met, wherein said second criterion is that the number of specified threads in said queue has not decreased since a specified prior time; and

responsive to said second criterion being met, deciding whether to enable said additional thread to access the shared resource before the second specified thread accesses the shared resource.

2. The method of claim 1, wherein:

responsive to deciding not to enable said additional thread to access the shared resource before the second specified thread, said additional thread is placed into said queue.

3. The method of claim 1, wherein:

said first prespecified criterion is that the number of threads retained in said queue during said identified time period is greater than one.

4. The method of claim 1, wherein:

said first prespecified criterion is that the number of threads retained in said queue during said identified time period is greater than a number which is determined from a specified relationship of the number of threads in the queue to the number of processors in said configuration of processors.

5. The method of claim 1, wherein:

said locking mechanism comprises a handoff lock mechanism that provides a lock, wherein the lock is sequentially acquired by different threads, and a thread becomes enabled to access the shared resource upon acquiring said lock.

6. The method of claim 5, wherein:

said second criterion is that the number of specified threads in said queue has not decreased since the last time the lock was acquired by a thread.

7. The method of claim 6, wherein:

a first counter is continually updated to show the current number of waiting threads in said queue at a given time, a second counter is continually updated to show the number of waiting threads each time the lock is acquired by a thread, and the contents of said first and second counters are selectively compared with each other to determine whether said second criterion has been met.

8. The method of claim 6, wherein:

said additional thread is enabled to access the shared resource when it is determined that said first criterion and said second criterion have been met, before said second specified thread acquires said lock.

9. The method of claim 1, wherein:

each processor of said configuration comprises a virtual processor.

10. The method of claim 1, wherein:

each processor of said configuration comprises a real processor.

11. In association with a plurality of processors including two or more processors that each provides a specified thread to access a shared resource, wherein the shared resource can only be accessed by one thread at a given time, a locking mechanism enables a first one of the specified threads to access the shared resource while each of the other specified threads is retained in a waiting queue, and a second one of the specified threads occupies a position of highest priority in the queue, a computer program product executable in a computer readable storage medium comprising:

instructions for identifying a time period between a time when the first specified thread releases access to the shared resource, and a later time when the second specified thread becomes enabled to access the shared resource;

instructions for responsive to an additional thread that is not one of the specified threads being provided by a processor to access the shared resource during the identified time period, for determining whether a first prespecified criterion pertaining to the specified threads retained in said queue has been met;

instructions for responsive to said first criterion being met, for determining whether a second prespecified criterion has been met, wherein said second criterion is that the number of specified threads in said queue has not decreased since a specified prior time; and

instructions for responsive to said second criterion being met, for deciding whether to enable said additional thread to access the shared resource before the second specified thread accesses the shared resource.

12. The computer program product of claim 11, wherein:

responsive to deciding not to enable said additional thread to access the shared resource before the second specified thread, said additional thread is placed into said queue.

13. The computer program product of claim 11, wherein:

said first prespecified criterion is that the number of threads retained in said queue during said identified time period is greater than one.

14. The computer program product of claim 11, wherein:

said locking mechanism comprises a handoff lock mechanism that provides a lock, wherein the lock is sequentially acquired by different threads, and a thread becomes enabled to access the shared resource upon acquiring said lock.

15. The computer program product of claim 14, wherein:

said second criterion is that the number of specified threads in said queue has not decreased since the last time the lock was acquired by a thread.

16. In association with a plurality of processors including two or more processors that each provides a specified thread to access a shared resource, wherein the shared resource can only be accessed by one thread at a given time, a locking mechanism enables a first one of the specified threads to access the shared resource while each of the other specified threads is retained in a waiting queue, and a second one of the specified threads occupies a position of highest priority in the queue, a apparatus comprising:

means for identifying a time period between a time when the first specified thread releases access to the shared resource, and a later time when the second specified thread becomes enabled to access the shared resource;

means responsive to an additional thread that is not one of the specified threads being provided by a processor to access the shared resource during the identified time period, for determining whether a first prespecified criterion pertaining to the specified threads retained in said queue has been met;

means responsive to said first criterion being met, for determining whether a second prespecified criterion has been met, wherein said second criterion is that the number of specified threads in said queue has not decreased since a specified prior time; and

means responsive to said second criterion being met, for deciding whether to enable said additional thread to access the shared resource before the second specified thread accesses the shared resource.

17. The apparatus of claim 16, wherein:

responsive to deciding not to enable said additional thread to access the shared resource before the second specified thread, said additional thread is placed into said queue.

18. The apparatus of claim 16, wherein:

said first prespecified criterion is that the number of threads retained in said queue during said identified time period is greater than one.

19. The apparatus of claim 16, wherein:

said locking mechanism comprises a handoff lock mechanism that provides a lock, wherein the lock is sequentially acquired by different threads, and a thread becomes enabled to access the shared resource upon acquiring said lock.

20. The apparatus of claim 19, wherein:

said second criterion is that the number of specified threads in said queue has not decreased since the last time the lock was acquired by a thread.