Blocking local sense synchronization barrier

• US 20070016905A1
• Filed: 07/12/2005
• Published: 01/18/2007
• Est. Priority Date: 07/12/2005
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Kishan, Arun, Clift, Neill, Rector, John, Morrison, Jonathan
• Granted Patent: US 7,770,170 B2
• Time in Patent Office: Days
• US Class Current: 718/100
• CPC Class Codes: G06F 9/52 Program synchronisation; Mutual exclusion, e.g. by means of semaphores
• CPC Class Codes: G06F 9/522 Barrier synchronisation
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database

Abstract

A blocking local sense synchronization barrier is provided. The local sense variable is not processor private or global, but truly local to the synchronization barrier function. Safe deletion is provided by making sure the last operation a thread performs on a barrier is a write. Just before returning, threads increment a field that indicates the count of threads that have left the barrier. Blocking is supported such that threads spin for some interval, and when they decide to block, examine and set (if not already set) the indication of whether a thread is blocking that is to be examined by the last thread to arrive at the barrier to determine whether to set an event to release blocking threads.

Claims

1. A method comprising:

synchronizing software threads via a synchronization barrier implemented via a synchronization barrier method; and

providing a variable that is to be changed within the synchronization barrier method, and read to determine when software threads should be released, wherein said variable is a local variable to the synchronization barrier method.

2. The method of claim 1 wherein the variable is known within a block of code associated with the method, but inaccessible to code outside the block.

3. The method of claim 1 wherein the value of the variable is not stored outside of the method.

4. The method of claim 1 wherein the value of the variable is not stored across calls to the synchronization barrier method.

11. A computer readable medium having instructions thereon for performing the method of claim 1.

12. A computer readable medium having instructions thereon for performing the method of claim 2.

13. A computer readable medium having instructions thereon for performing the method of claim 3.

14. A computer readable medium having instructions thereon for performing the method of claim 4.

5. A method comprising:

synchronizing software threads via a synchronization barrier implemented via a synchronization barrier method; and

ensuring a last operation a thread performs while in the synchronization barrier method is a write to ensure safe deletion of the barrier.

6. The method of claim 5 wherein the ensuring act comprises:

maintaining a count of variables which have left the synchronization barrier.

7. The method of claim 5 wherein the maintaining act comprises:

setting a field to be a predetermined value by a last thread to arrive at the barrier before releasing other threads from the barrier; and

incrementing the field by the other threads before each returns.

8. The method of claims 5 further comprises:

using an indication of whether a thread is blocking to determine whether a thread is blocking;

resetting a previous event by a last thread to arrive at the barrier;

determining whether to reset a current event by the last thread to arrive at the barrier by examining the indication of whether a thread is blocking;

releasing spinning threads waiting for the last thread to arrive at the barrier; and

setting a current event by the last thread to arrive at the barrier to release threads that are blocking while waiting for the last thread to arrive if indicated to do so by the examination of the indication of whether a thread is blocking.

9. The method of claim 8 wherein the act of using an indication of whether a thread is blocking to determine whether a thread is blocking comprises:

examining the indication of whether a thread is blocking by a thread deciding to block;

setting the indication of whether a thread is blocking by a thread deciding to block, if the indication of whether a thread is blocking is not set, in order to indicate that the last thread to arrive at the barrier must set the event;

examining a variable by the thread deciding to block that indicates whether the last thread has arrived at the barrier;

waiting by blocking until the event is set, if the variable examined indicated that the last thread has not arrived at the barrier.

15. A computer readable medium having instructions thereon for performing the method of claim 5.

16. A computer readable medium having instructions thereon for performing the method of claim 6.

17. A computer readable medium having instructions thereon for performing the method of claim 7.

18. A computer readable medium having instructions thereon for performing the method of claim 8.

19. A computer readable medium having instructions thereon for performing the method of claim 9.

10. A method comprising:

synchronizing software threads via a synchronization barrier implemented via a synchronization barrier method;

providing a variable that is to be changed within the synchronization barrier method, and examined to determine when software threads should be released, wherein said variable is a local variable to the synchronization barrier method;

ensuring the last operation a thread performs while in the synchronization barrier method is a write to ensure safe deletion of the barrier by maintaining a count of variables which have left the synchronization barrier;

using an indication of whether a thread is blocking to determine whether a thread is blocking;

resetting a previous event by a last thread to arrive at the barrier;

determining whether to reset a current event by the last thread to arrive at the barrier by examining the indication of whether a thread is blocking;

releasing spinning threads waiting for the last thread to arrive at the barrier;

setting a current event by the last thread to arrive at the barrier to release threads that are blocking while waiting for the last thread to arrive, if indicated to do so by the examination of the indication of whether a thread is blocking, and wherein the indication of whether a thread is blocking is created only at a time when a thread decides to block.

20. A computer readable medium having instructions thereon for performing the method of claim 10.