Semaphore with Timeout and Lock-Free Fast Path for Message Passing Architectures

• US 20140310438A1
• Filed: 04/10/2013
• Published: 10/16/2014
• Est. Priority Date: 04/10/2013
• Status: Active Grant

• Current Assignee: Wind River Systems Incorporated (Aptiv PLC)
• Original Assignee: Wind River Systems Incorporated (Aptiv PLC)
• Inventors: RICHARDSON, Raymond, Stults, Gregory
• Granted Patent: US 9,772,888 B2
• Time in Patent Office: Days
• US Class Current: 710/200
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

The exemplary embodiments describe systems and methods for utilizing a semaphore with timeout and lock-free path for message passing architectures. One embodiment is related to a method comprising receiving a request from a client to access an object, the object including a plurality of resources, placing the request in a lock-free pend queue of a semaphore, manipulating a count of the semaphore based on an availability of at least one of the plurality of resources, and determining whether the client can use a fast path to the object.

Claims

1. A method, comprising:

receiving a request from a client to access an object, the object including a plurality of resources;

placing the request in a lock-free pend queue of a semaphore;

manipulating a count of the semaphore based on an availability of at least one of the plurality of resources; and

determining whether the client can use a fast path to the object.

2. The method of claim 1, further comprising:

releasing a thread from the lock-free pend queue upon receiving a pend message.

3. The method of claim 1, wherein the count of the semaphore includes a release count and an in-flight release count.

4. The method of claim 3, further comprising:

incrementing the release count when the lock-free pend queue is empty;

releasing a thread immediately upon receiving a pend message; and

decrementing the release count upon release.

5. The method of claim 1, further comprising:

tracking elapsed time to manage semaphore timeouts; and

releasing a thread having an expired timeout.

6. The method of claim 1, wherein lock-free pend queue is a data structure capable of maintaining a specified order scheme of blocked clients on the semaphore.

7. The method of claim 1, wherein the lock-free pend queue is maintained by a single chain of execution accessing the object atomically.

8. The method of claim 1, wherein the fast path is free of messaging and blocking.

9. A system, comprising:

an object including a plurality of resources;

a semaphore including a lock-free pend queue and a decision variable; and

an iso-locator core receiving a request from a client to access the object, placing the request in the lock-free pend queue of the semaphore, manipulating the decision variable of the semaphore based on an availability of at least one of the plurality of resources, and determining whether the client can use a fast path to the object.

10. The system of claim 9, wherein the iso-locator core further releases a thread from the lock-free pend queue upon receive a pend message.

11. The system of claim 9, wherein the count of the semaphore includes a release count and an in-flight release count.

12. The system of claim 11, wherein the iso-locator core further increments the release count when the lock-free pend queue is empty, releases a thread immediately upon receiving a pend message, and decrements the release count upon release.

13. The system of claim 9, wherein the iso-locator core further tracks elapsed time to manage semaphore timeouts, and releases a thread having an expired timeout.

14. The system of claim 9, wherein lock-free pend queue is a data structure capable of maintaining a specified order scheme of blocked clients on the semaphore.

15. The system of claim 9, wherein the iso-locator core is a single chain of execution accessing the object atomically.

16. The system of claim 9, wherein the fast path is free of messaging and blocking.

17. A computer readable storage medium including a set of instructions executable by a processor, the set of instructions operable to:

receive a request from a client to access an object, the object including a plurality of resources;

place the request in a lock-free pend queue of a semaphore;

manipulate a count of the semaphore based on an availability of at least one of the plurality of resources; and

determine whether the client can use a fast path to the object.

18. The computer readable storage medium of claim 17, wherein the instructions are further operable to:

increment the release count when the lock-free pend queue is empty;

release a thread immediately upon receiving a pend message; and

decrement the release count upon release.

19. The computer readable storage medium of claim 17, wherein the instructions are further operable to:

track elapsed time to manage semaphore timeouts; and

release a thread having an expired timeout.

20. The computer readable storage medium of claim 17, wherein lock-free pend queue is a data structure capable of maintaining a specified order scheme of blocked clients on the semaphore.