Inter-processor competition for a shared resource

• US 7,111,298 B1
• Filed: 09/04/2001
• Issued: 09/19/2006
• Est. Priority Date: 09/04/2001
• Status: Expired due to Term

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Sade, Gilad, Michael, Ofer, Lim, Clifford
• Primary Examiner(s): BULLOCK JR, LEWIS ALEXANDER
• Application Number:
  US09/945,939
• Time in Patent Office: 1,841 Days
• Field of Search: 718100-108
• US Class Current: 718/104
• CPC Class Codes: G06F 2209/521 Atomic
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

In a multi-processor system in which several processors compete for exclusive use of a shared resource, a claimant processor asserts exclusive access to a resource by determining whether there exists a competing claim to exclusive access to said resource and then posting a claim to exclusive access to said resource. Following lapse of an interval, the claimant processor then determines whether there exists a competing claim to exclusive access to said resource. Depending on whether or not such a claim exists, the claimant processor then either takes control of the resource or makes another attempt after waiting.

Claims

1. In a data-storage system having resources to be shared among processors, a method for asserting exclusive access to a resource by a first processor, said method comprising:

selecting an extent of a first interval on the basis of a time required for the processors to read from and write to a location accessible to the processors;

determining whether there exists a competing claim to exclusive access to said resource by another processor;

posting, at the location accessible to the processors, a claim to exclusive access to said resource by said first processor;

determining whether there exists a competing claim to exclusive access to said resource by another processor, following lapse of said first interval that begins with the posting of the claim; and

determining whether there exists a competing claim to exclusive access to said resource by another processor, following lapse of a second interval that begins after the lapse of the first interval, wherein the second interval is selected on the basis of an expected usage time for said resource.

2. The method of claim 1, wherein determining that there exists a competing claim comprises inspecting a data-storage location to determine whether exclusive access to said resource has already been claimed.

3. The method of claim 2, wherein inspecting a data-storage location comprises determining whether said data-storage location includes a release code indicating that said resource has been released by a competitor.

4. The method of claim 1, wherein posting a claim of exclusive access comprises replacing data at a data-storage location with a claim code indicating a claim to exclusive access to said resource.

5. The method of claim 1, wherein determining whether there exists a competing claim following lapse of a first interval comprises determining whether said claim to exclusive access continues to be posted.

6. The method of claim 1, further comprising selecting an extent of said first interval on the basis of a time associated with determining whether there exists a competing claim and posting a claim to exclusive access.

7. The method of claim 1, further comprising selecting said second interval to be different from second intervals associated with competing claims for access to said resource.

8. The method of claim 1, wherein posting a claim to exclusive access further comprises posting, at a location accessible to the plurality of potential claimants, a time at which the claim of exclusive access is made.

9. The method of claim 1 further comprising asserting exclusive access to a resource after a third interval that begins with the posting of the claim.

10. A computer-readable medium having encoded thereon software for causing a first processor in a set of processors to assert exclusive access to a resource accessible by said set of processors, said software comprising instructions for:

selecting an extent of a first interval on the basis of a time required for said processors to read from and write to a location accessible to said processors

determining whether there exists a competing claim to exclusive access to said resource by another processor;

posting, at the location accessible to said processors, a claim to exclusive access to said resource by the first processor;

determining whether there exists a competing claim to exclusive access to said resource following lapse of said first interval that begins with the posting of the claim; and

determining whether there exists a competing claim to exclusive access to said resource following lapse of a second interval that begins after the lapse of said first interval, wherein the second interval is selected on the basis of an expected usage time for said resource.

11. The computer-readable medium of claim 10, wherein said instructions for determining whether there exists a competing claim comprise instructions for inspecting a data-storage location to determine whether exclusive access to said resource has already been claimed.

12. The computer-readable medium of claim 11, wherein said instructions for inspecting a data-storage location comprise instructions for determining whether said data-storage location includes a release code indicating that said resource has been released by a competitor.

13. The computer-readable medium of claim 10, wherein said instructions for posting a claim of exclusive access comprise instructions for replacing data at a data-storage location with a claim code indicating a claim to exclusive access to said resource.

14. The computer-readable medium of claim 10, wherein said instructions for determining whether there exists a competing claim following lapse of a first interval comprise instructions for determining whether said claim to exclusive access continues to be posted.

15. The computer-readable medium of claim 10, wherein said software further comprises instructions for selecting an extent of said first interval on the basis of a time associated with determining whether there exists a competing claim, and posting a claim to exclusive access.

16. The computer-readable medium of claim 10, wherein said software further comprises instructions for selecting said second interval to be different from second intervals associated with competing claims for access to said resource.

17. The computer-readable medium of claim 10, wherein posting a claim to exclusive access of said resource further comprises posting, at a location accessible to the plurality of potential claimants, a time at which the claim of exclusive access is made.

18. The computer-readable medium of claim 10, wherein said software further comprises instructions for asserting exclusive access to a resource after a third interval that begins with the posting of the claim.