Method for resource lock/unlock capability in multithreaded computer environment

• US 6,112,222 A
• Filed: 08/25/1998
• Issued: 08/29/2000
• Est. Priority Date: 08/25/1998
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Govindaraju, Rama K., Tuel, William G. Jr., Kon, Elizabeth Anne, Straub, Robert Michael
• Primary Examiner(s): BANANKHAH, MAJID A
• Application Number:
  US09/139,816
• Time in Patent Office: 735 Days
• Field of Search: 709/100, 709/102, 709/103, 709/105, 709/108, 709/300, 709/101, 709/104
• US Class Current: 718/102
• CPC Class Codes: G06F 9/3004 to perform operations on memory
• CPC Class Codes: G06F 9/30087 Synchronisation or serialisation instructions
• CPC Class Codes: G06F 9/52 Program synchronisation; Mutual exclusion, e.g. by means of semaphores

Abstract

Hybrid lock and unlock capabilities are provided for a threaded computing environment. For example, kernel locking services are selectively employed in conjunction with functions in the POSIX threads standard to provide a lock capability and an unlock capability. The hybrid approach determines which lock scheme to employ by evaluating whether one thread or multiple threads concurrently desire a resource lock. When only one thread desires the lock, the thread is directly assigned resource ownership employing one of an operating system primitive lock process or a hardware lock process. An alternate lock process is used to obtain resource ownership when multiple threads concurrently desire the lock. This alternate process employs at least one function in the POSIX threads standard to implement a queue of waiting threads. A similar hybrid approach to the unlock capability is also provided.

Claims

1. A method for obtaining a lock on a resource in a multithread computer environment, said method comprising:

determining whether one thread or multiple threads desire said lock on said resource;

directly assigning resource ownership to said one thread when said determining determines only said one thread to be actively seeking said lock on said resource, said directly assigning employing a first lock process comprising one of an operating system primitive lock process or a hardware lock process; and

employing a second lock process to obtain said lock on said resource when said determining determines that multiple threads concurrently desire ownership of said resource, said second lock process employing at least one function in the POSIX threads standard.

2. The method of claim 1, further comprising obtaining said lock employing a lock structure, wherein said lock structure includes a lock.owner field representative of thread ownership of said lock.

3. The method of claim 2, wherein said lock structure further comprises a lock.status field representative of ownership of said lock structure, and wherein said determining comprises initially obtaining ownership of said lock structure by setting said lock.status before determining whether one thread or multiple threads desire said lock on said resource.

4. The method of claim 3, wherein said lock structure further includes a lock.waiter field representative of a number of threads waiting for said lock, and wherein said determining comprises evaluating said lock.waiters field and said lock.owner field to ascertain whether only said one thread actively desires said lock on said resource.

5. The method of claim 4, wherein said second lock process comprises incrementing said lock.waiters, releasing said lock.status, and implementing a queue of waiting threads when said determining determines that multiple threads concurrently desire ownership of said resource.

6. The method of claim 5, wherein said implementing said queue of waiting threads comprises employing a mutex function and a condition wait function of the POSIX threads standard.

7. The method of claim 6, further comprising allocating at initialization of a user of said multithread computer environment a "mutex" and a "cond" structure for use in implementing said mutex function and said wait condition function.

8. The method of claim 5, wherein said second lock process further comprises decrementing said control.waiters after obtaining said lock on said resource, said decrementing of said control.waiters being preceded by a compare and swap function to set said lock.status field.

9. The method of claim 1, wherein said second lock process employs said at least one function in the POSIX threads standard to implement a queue of threads waiting for said lock on said resource, said at least one function in the POSIX threads standard comprising a mutex function and a condition wait function.

10. The method of claim 1, wherein said computer environment comprises an AIX based multiprocessor system, and wherein said first lock process comprises an AIX kernel process.

11. The method of claim 1, wherein said resource comprises a threaded message passing interface (MPI) library.

12. The method of claim 1, wherein said first lock process comprises said operating system primitive lock process, and wherein said operating system primitive lock process comprises a single word compare and swap instruction.

13. The method of claim 12, wherein said computer environment comprises an AIX based multiprocessor system, and wherein said single word compare and swap instruction comprises a direct AIX kernel call.

14. A method for unlocking a lock on a resource in a multithread computer environment, said lock employing a lock structure including a lock.owner field representative of thread ownership of said resource, a lock.status field representative of ownership of said lock structure, and a lock.waiters field representative of a count of threads waiting to obtain said lock, said method comprising:

obtaining control of said lock structure by setting said lock.status field;

determining whether any threads are waiting for said lock by evaluating said lock.waiters field; and

if no threads are waiting, directly setting said lock.owner field to null, otherwise employing at least one function in the POSIX threads standard to set said lock.owner field to null and issue a thread condition signal to waiting threads that said resource has been unlocked.

15. The method of claim 14, wherein said at least one function in the POSIX threads standard comprises a mutex function and a thread condition signal function, and wherein said mutex function employs a "mutex" structure and said thread condition signal employs a "cond" structure, said "mutex" structure and said "cond" structure being provided by a user of said multithread computer environment.

16. The method of claim 15, further comprising releasing said lock.status after setting said lock.owner to null.

17. The method of claim 14, wherein said multithread computer environment comprises an AIX based multi-processor system.