Updating shared variables atomically

• US 8,495,311 B2
• Filed: 06/25/2009
• Issued: 07/23/2013
• Est. Priority Date: 06/25/2009
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Martin, Andrew K.
• Primary Examiner(s): Shah, Sanjiv
• Assistant Examiner(s): DILLON, SAMUEL A
• Application Number:
  US12/491,689
• Publication Number:
  US 20100332769A1
• Time in Patent Office: 1,489 Days
• Field of Search: 711/155, 711/150, 711/152, 711/167
• US Class Current: 711/155
• 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 a plurality of variables for an atomic transaction, wherein the atomic transaction comprises reading the plurality of variables and performing work and updating the plurality of variables;

responsive to the completion of reading the plurality of variables, attempting to acquire a plurality of locks corresponding to the plurality of variables, wherein the attempt to acquire the plurality of locks is unsuccessful if reading the plurality of variables and attempting to acquire the plurality of locks takes longer than a predetermined time period;

responsive to the attempt to acquire the plurality of locks being successful, performing work and updating the plurality of variables; and

responsive to the completion of performing and updating the plurality of variables, waiting the predetermined time period prior to releasing the plurality of locks.

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

6. The method of claim 1, wherein the predetermined time period is a predetermined number of clock cycles based on a number of variables in the plurality of variables.

3. The method of claim further comprising:

responsive to the attempt to acquire the plurality of locks being unsuccessful, retrying the atomic transaction.

4. The method of claim 3, wherein retrying the atomic transaction comprises flushing the plurality of variables and re-reading the plurality of variables.

5. The method of claim 3, wherein retrying the atomic transaction comprises increasing the predetermined time period.

7. A computer program product comprising a non-transitory computer readable storage medium having a computer readable program stored thereon, wherein the computer readable program, when executed on a computing device, causes the computing device to:

read a plurality of variables for an atomic transaction, wherein the atomic transaction comprises reading the plurality of variables and performing work and updating the plurality of variables;

responsive to the completion of reading the plurality of variables, attempt to acquire a plurality of locks corresponding to the plurality of variables, wherein the attempt to acquire the plurality of locks is unsuccessful if reading the plurality of variables and attempting to acquire the plurality of locks takes longer than a predetermined time period;

responsive to the attempt to acquire the plurality of locks being successful, perform work and update the plurality of variables; and

responsive to the completion of performing and updating the plurality of variables, wait the predetermined time period prior to releasing the plurality of locks.

8. The computer program product of claim 7, wherein the attempt to acquire the plurality of locks is unsuccessful if another thread has at least one of the plurality of locks.

9. The computer program product of claim 7, wherein the computer readable program further causes the computing device to:

responsive to the attempt to acquire the plurality of locks being unsuccessful, retry the atomic transaction.

10. The computer program product of claim 9, wherein retrying the atomic transaction comprises flushing the plurality of variables and re-reading the plurality of variables.

11. The computer program product of claim 9, wherein retrying the atomic transaction comprises increasing the predetermined time period.

12. The computer program product of claim 7, 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.

13. The computer program product of claim 7, 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.

14. The computer program product of claim 7, wherein the predetermined time period is a predetermined number of clock cycles based on a number of variables in the plurality of variables.

15. An apparatus, comprising:

a processing unit executing a thread;

a shared memory; and

a locking component coupled to the shared memory, wherein responsive to the completion of reading a plurality of variables from the shared memory for an atomic transaction from the thread, the locking component is configured to attempt to acquire a plurality of locks corresponding to the plurality of variables, wherein the atomic transaction comprises reading the plurality of variables and performing work and updating the plurality of variables, wherein the attempt to acquire the plurality of locks is unsuccessful if reading the plurality of variables and attempting to acquire the plurality of locks takes longer than a predetermined time period;

wherein responsive to the attempt to acquire the plurality of locks being successful, the thread is configured to perform work and update the plurality of variables in the shared memory; and

wherein responsive to the completion of performing work and updating the plurality of variables, the locking component is configured to wait the predetermined time period prior to releasing the plurality of locks.

16. The apparatus of claim 15, wherein the attempt to acquire the plurality of locks is unsuccessful if another thread has at least one of the plurality of locks.

17. The apparatus of claim 15, wherein the locking component is further configured to:

responsive to the attempt to acquire the plurality of locks being unsuccessful, retry the atomic transaction.

18. The apparatus of claim 17, wherein retrying the atomic transaction comprises flushing the plurality of variables and re-reading the plurality of variables.

19. The apparatus of claim 17, wherein retrying the atomic transaction comprises increasing the predetermined time period.

20. The apparatus of claim 15, wherein the predetermined time period is a predetermined number of clock cycles based on a number of variables in the plurality of variables.