DETERMINING WHEN TO RELEASE A LOCK FROM A FIRST TASK HOLDING THE LOCK TO GRANT TO A SECOND TASK WAITING FOR THE LOCK

• US 20180011744A1
• Filed: 07/06/2016
• Published: 01/11/2018
• Est. Priority Date: 07/06/2016
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Liguori, Gregg L., McCune, Franklin E., Reed, David C., Scott, Michael R.
• Granted Patent: US 11,157,332 B2
• Time in Patent Office: Days
• CPC Class Codes: G06F 9/4881 Scheduling strategies for dispatcher, e.g. round robin, multi-level priority queues
• CPC Class Codes: G06F 9/5038 considering the execution order of a plurality of tasks, e.g. taking priority or time dependency constraints into consideration scheduling strategies G06F9/4881 and subgroups
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

Provided are a computer program product, system, and method for determining when to release a lock from a first task holding the lock to grant to a second task waiting for the lock. A determination is made as to whether a holding of a lock to the resource by a first task satisfies a condition and whether the lock is swappable. The lock is released from the first task and granted to a second task waiting in a queue for the lock in response to determining that the holding of the lock satisfies the condition and that the lock is swappable. The first task is indicated in the queue waiting for the lock in response to granting the lock to the second task.

Claims

1. A computer program product for managing access to a resource in a computer system, the computer program product comprising a computer readable storage medium having computer readable program code embodied therein that when executed performs operations, the operations comprising:

determining whether a holding of a lock to the resource by a first task satisfies a condition and whether the lock is swappable;

releasing the lock from the first task and granting the lock to a second task waiting in a queue for the lock in response to determining that the holding of the lock satisfies the condition and that the lock is swappable; and

indicating the first task in the queue waiting for the lock in response to granting the lock to the second task.

2. The computer program product of claim 1, wherein the holding of the lock satisfies the condition when the first task holds the lock for a predetermined time.

3. The computer program product of claim 1, wherein the holding of the lock satisfies the condition when the first task holds the lock for a predetermined time when the second task comprises a highest priority task.

4. The computer program product of claim 1, wherein the queue includes a plurality of tasks waiting for the lock, wherein the second task to which the lock is granted is a first waiter in the queue to receive the lock when released, and wherein the first task is added to the queue as the first waiter in the queue to receive the lock when released by the second task.

5. The computer program product of claim 1, wherein the operations further comprise:

indicating the lock as swappable when the first task or second task holding the lock is waiting for at least one additional resource while holding the lock that is needed to complete a task operation using the resource; and

indicating the lock as unswappable in response to at least one of the first task or second task holding the lock initiating processing of the resource to perform the task operation;

the first task or the second task holding the lock changing content of the resource;

the first task or the second task holding the lock obtaining access to the at least one additional resource needed to complete the task operation using the resource for which the lock is held; and

the first task or the second task holding the lock obtaining at least one lock to the at least one additional resource needed to complete the task operation using the resource for which the lock is held, wherein when the releasing the lock from the first task and the granting the lock to the second task are only performed if the lock is indicated as swappable and not indicated as unswappable.

6. The computer program product of claim 1, wherein the first task holding the lock performs the determining whether the holding the lock satisfies the condition and whether the lock is swappable, wherein the operations further comprise:

calling, by the first task, a swap function to cause the releasing of the lock from the first task, the granting of the lock to the second task, and the indicating the first task in the queue waiting for the lock in response to the first task determining that the holding of the lock satisfies the condition and that the lock is swappable.

7. The computer program product of claim 1, wherein a resource manager monitoring tasks accesses to resources and locks to the resources performs the operations of determining whether the holding of the lock satisfies the condition, whether the lock is swappable, the releasing the lock, the granting the lock, and the indicting the first task in the queue waiting for the lock.

8. The computer program product of claim 1, wherein a swap operation comprises the releasing the lock, the granting the lock, and the indicating the first task in the queue waiting for the lock, wherein the holding of the lock does not satisfy the condition if the swap operation has been performed a maximum number of times before the first task has released the lock after completing a task operation using the resource of the lock.

9. The computer program product of claim 1, wherein a swap operation comprises the releasing the lock, the granting the lock, and the indicating the first task in the queue waiting for the lock, wherein the holding of the lock does not satisfy the condition if the swap operation has been performed a maximum number of times to release the lock to grant to a task having a lower priority than the first task before the first task has released the lock after completing a task operation using the resource of the lock.

10. The computer program product of claim 1, wherein the operations further comprise:

determining whether the second task in the queue has a higher priority than the first task, wherein the releasing the lock, the granting the lock, and the indicting the first task in the queue waiting for the lock are performed in response to the determining that the holding of the lock satisfies the condition, that the lock is swappable and that the second task in the queue has the higher priority than the first task.

11. The computer program product of claim 1, wherein the determining whether the holding of the lock satisfies the condition comprises determining that the first task has the lock for a predetermined time and additionally determining that the holding of the lock satisfies at least one condition that are members of a set of satisfied conditions consisting of:

a swap operation, comprising the releasing the lock, the granting the lock, and the indicating the first task in the queue, having been performed less than a maximum number of times before the first task has released the lock after completing a task operation;

the swap operation having been performed less than a maximum number of times to release the lock to grant to a task having a lower priority than the first task before the first task has released the lock after completing the task operation; and

that the second task in the queue has a higher priority than the first task holding the lock.

12. A computer program product for managing access to a resource in a computer system, the computer program product comprising a computer readable storage medium having computer readable program code embodied therein that when executed performs operations, the operations comprising:

determining whether a lock to the resource has been held by a first task for a predetermined time while the first task waits for at least one additional resource;

releasing the lock from the first task and granting the lock to a second task waiting in a queue for the lock in response to determining that the first task has held the lock for the predetermined time while waiting for the at least one additional resource; and

indicating the first task in the queue waiting for the lock in response to granting the lock to the second task.

13. The computer program product of claim 12, wherein the waiting for the at least one additional resource comprises waiting for at least one additional lock to the at least one additional resource, wherein the first task requires the lock and the at least one additional lock in order to complete an operation using the resource.

14. A system for managing access to a resource, comprising:

a processor; and

a computer readable storage medium having computer readable program code embodied therein that when executed by the processor performs operations, the operations comprising;

determining whether a holding of a lock to the resource by a first task satisfies a condition and whether the lock is swappable;

releasing the lock from the first task and granting the lock to a second task waiting in a queue for the lock in response to determining that the holding of the lock satisfies the condition and that the lock is swappable; and

indicating the first task in the queue waiting for the lock in response to granting the lock to the second task.

15. The system of claim 14, wherein the holding of the lock satisfies the condition when the first task holds the lock for a predetermined time.

16. The system of claim 14, wherein the queue includes a plurality of tasks waiting for the lock, wherein the second task to which the lock is granted is a first waiter in the queue to receive the lock when released, and wherein the first task is added to the queue as the first waiter in the queue to receive the lock when released by the second task.

17. The system of claim 14, wherein the operations further comprise:

indicating the lock as swappable when the first task or second task holding the lock is waiting for at least one additional resource while holding the lock that is needed to complete a task operation using the resource; and

indicating the lock as unswappable in response to at least one of;

the first task or second task holding the lock initiating processing of the resource to perform the task operation;

the first task or the second task holding the lock changing content of the resource;

the first task or the second task holding the lock obtaining access to the at least one additional resource needed to complete the task operation using the resource for which the lock is held; and

the first task or the second task holding the lock obtaining at least one lock to the at least one additional resource needed to complete the task operation using the resource for which the lock is held, wherein when the releasing the lock from the first task and the granting the lock to the second task are only performed if the lock is indicated as swappable and not indicated as unswappable.

18. The system of claim 14, wherein a swap operation comprises the releasing the lock, the granting the lock, and the indicating the first task in the queue waiting for the lock, wherein the holding of the lock does not satisfy the condition if the swap operation has been performed a maximum number of times to release the lock to grant to a task having a lower priority than the first task before the first task has released the lock after completing a task operation using the resource of the lock.

19. The system of claim 14, wherein a swap operation comprises the releasing the lock, the granting the lock, and the indicating the first task in the queue waiting for the lock, wherein the holding of the lock does not satisfy the condition if the swap operation has been performed a maximum number of times to release the lock to grant to a task having a lower priority than the first task before the first task has released the lock after completing a task operation using the resource of the lock.

20. A method for managing access to a resource in a computer system, comprising:

determining whether a holding of a lock to the resource by a first task satisfies a condition and whether the lock is swappable;

releasing the lock from the first task and granting the lock to a second task waiting in a queue for the lock in response to determining that the holding of the lock satisfies the condition and that the lock is swappable; and

indicating the first task in the queue waiting for the lock in response to granting the lock to the second task.

21. The method of claim 20, wherein the holding of the lock satisfies the condition when the first task holds the lock for a predetermined time.

22. The method of claim 20, wherein the queue includes a plurality of tasks waiting for the lock, wherein the second task to which the lock is granted is a first waiter in the queue to receive the lock when released, and wherein the first task is added to the queue as the first waiter in the queue to receive the lock when released by the second task.

23. The method of claim 20, further comprising:

indicating the lock as swappable when the first task or second task holding the lock is waiting for at least one additional resource while holding the lock that is needed to complete a task operation using the resource; and

indicating the lock as unswappable in response to at least one of;

the first task or second task holding the lock initiating processing of the resource to perform the task operation;

the first task or the second task holding the lock changing content of the resource;

the first task or the second task holding the lock obtaining access to the at least one additional resource needed to complete the task operation using the resource for which the lock is held; and

the first task or the second task holding the lock obtaining at least one lock to the at least one additional resource needed to complete the task operation using the resource for which the lock is held, wherein when the releasing the lock from the first task and the granting the lock to the second task are only performed if the lock is indicated as swappable and not indicated as unswappable.

24. The method of claim 20, wherein a swap operation comprises the releasing the lock, the granting the lock, and the indicating the first task in the queue waiting for the lock, wherein the holding of the lock does not satisfy the condition if the swap operation has been performed a maximum number of times to release the lock to grant to a task having a lower priority than the first task before the first task has released the lock after completing a task operation using the resource of the lock.

25. The method of claim 20, wherein a swap operation comprises the releasing the lock, the granting the lock, and the indicating the first task in the queue waiting for the lock, wherein the holding of the lock does not satisfy the condition if the swap operation has been performed a maximum number of times to release the lock to grant to a task having a lower priority than the first task before the first task has released the lock after completing a task operation using the resource of the lock.