Updating Shared Variables Atomically

• US 20100332769A1
• Filed: 06/25/2009
• Published: 12/30/2010
• Est. Priority Date: 06/25/2009
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Martin, Andrew K.
• Granted Patent: US 8,495,311 B2
• Time in Patent Office: Days
• US Class Current: 711/147
• CPC Class Codes: G06F 12/00 Accessing, addressing or allocating within memory systems or architectures digital input from, or digital output to record carriers, e.g. to disk storage units, G06F3/06
• CPC Class Codes: G06F 12/14 Protection against unauthorised use of memory or access to memory
• CPC Class Codes: G06F 2209/521 Atomic
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

When a thread begins an atomic transaction, the thread reads one or more variables from one or more source addresses. The read portion of the transaction is constrained to a predetermined amount of time or number of cycles (N). The mechanism then performs a test and set operation to determine whether any other threads hold locks on the one or more source addresses. If the locks for the one or more source addresses are free, then the thread acquires locks on the one or more source addresses. The thread then performs work and updates the one or more variables. Thereafter, the mechanism delays for an amount of time or number of cycles greater than or equal to N before releasing the locks. If another thread attempts to acquire a lock on the one or more source addresses, then the test and set operation for that other thread will fail.

Claims

1. A method, in a data processing system, for performing a transaction to update shared variables atomically, the method comprising:

reading one or more variables for a transaction;

responsive to reading the one or more variables, attempting to acquire one or more locks corresponding to the one or more variables;

responsive to the attempt to acquire the one or more locks being successful, performing work and updating the one or more variables; and

waiting a predetermined time period prior to releasing the one or more locks.

2. The method of claim 1, wherein the attempt to acquire the one or more locks is unsuccessful if another thread has at least one of the one or more locks.

3. The method of claim 1, wherein the attempt to acquire the one or more locks is unsuccessful if reading the one or more variables and attempting to acquire the one or more locks takes longer than the predetermined time period.

4. The method of claim 1, further comprising:

responsive to the attempt to acquire the one or more locks being unsuccessful, retrying the transaction.

5. The method of claim 4, wherein retrying the transaction comprises flushing the one or more variables and re-reading the one or more variables.

6. The method of claim 4, wherein retrying the transaction comprises increasing the predetermined time period.

7. The method of claim 1, wherein the predetermined time period is a predetermined number of clock cycles.

14. The computer program product of claim 1, wherein the computer readable program is stored in a computer readable storage medium in a data processing system and wherein the computer readable program was downloaded over a network from a remote data processing system.

15. The computer program product of claim 1, wherein the computer readable program is stored in a computer readable storage medium in a server data processing system and wherein the computer readable program is downloaded over a network to a remote data processing system for use in a computer readable storage medium with the remote system.

8. A computer program product comprising a computer recordable medium having a computer readable program recorded thereon, wherein the computer readable program, when executed on a computing device, causes the computing device to:

read one or more variables;

responsive to reading the one or more variables, attempt to acquire one or more locks corresponding to the one or more variables;

responsive to the attempt to acquire the one or more locks being successfiul, perform work and update the one or more variables; and

wait a predetermined time period prior to releasing the one or more locks.

9. The computer program product of claim 8, wherein the attempt to acquire the one or more locks is unsuccessful if another thread has at least one of the one or more locks.

10. The computer program product of claim 8, wherein the attempt to acquire the one or more locks is unsuccessful if reading the one or more variables and attempting to acquire the one or more locks takes longer than the predetermined time period.

11. The computer program product of claim 8, wherein the computer readable program further causes the computing device to:

responsive to the attempt to acquire the one or more locks being unsuccessful, retry the transaction.

12. The computer program product of claim 11, wherein retrying the transaction comprises flushing the one or more variables and re-reading the one or more variables.

13. The computer program product of claim 11, wherein retrying the transaction comprises increasing the predetermined time period.

16. An apparatus, comprising:

a shared memory; and

a locking component coupled to the shared memory, wherein the locking component is configured to;

responsive to reading one or more variables from the shared memory, attempt to acquire one or more locks corresponding to the one or more variables;

responsive to the attempt to acquire the one or more locks being successfiu, perform work and update the one or more variables in the shared memory; and

wait a predetermined time prior to releasing the one or more locks.

17. The apparatus of claim 16, wherein the attempt to acquire the one or more locks is unsuccessful if another thread has at least one of the one or more locks.

18. The apparatus of claim 16, wherein the attempt to acquire the one or more locks is unsuccessful if reading the one or more variables and attempting to acquire the one or more locks takes longer than the predetermined time period.

19. The apparatus of claim 16, wherein the locking component is further configured to:

responsive to the attempt to acquire the one or more locks being unsuccessful, retry the transaction.

20. The apparatus of claim 19, wherein retrying the transaction comprises increasing the predetermined time period.