Mechanism for managing the locking and unlocking of objects in Java

• US 6,411,983 B1
• Filed: 04/28/1998
• Issued: 06/25/2002
• Est. Priority Date: 11/27/1997
• Status: Expired due to Term

• Current Assignee: X Corp. (f/k/a Twitter, Inc.) (X Holdings Corp.)
• Original Assignee: International Business Machines Corporation
• Inventors: Gallop, Patrick George
• Primary Examiner(s): Oberley, Alvin
• Assistant Examiner(s): Lao, S.
• Application Number:
  US09/067,577
• Time in Patent Office: 1,519 Days
• Field of Search: 709/100, 709/102, 709/104, 709/107, 707/8, 707/206, 711/6
• US Class Current: 718/104
• CPC Class Codes: G06F 9/52 Program synchronisation; Mutual exclusion, e.g. by means of semaphores

Abstract

A mechanism for managing the locking and unlocking of objects. The mechanism comprises a transition vector having an ordered set of transition elements. Each of the transition elements includes a locking function or a pointer to the locking function and an unlocking function or a pointer to the unlocking function. When an object is created a transition vector is assigned to the object. The object includes a reference element which references a transition element in the vector. In response to a request to lock the object, the locking function in the transition element is invoked and the next transition element is assigned to the object and the reference element in the object is updated. For a request to unlock the object, the unlocking function in the transition element is invoked and the previous transition element is assigned to the object and the reference element is updated. The mechanism improves execution overhead by providing an implicit count for determining the lock count on an object. The mechanism also features typed transition vectors for structured locking/unlocking and unstructured locking/unlocking operations.

Claims

1. A mechanism for managing the locking and unlocking of an object by a thread, said mechanism comprising:

(a) a transition vector having a plurality of ordered transition elements, each of said plurality of ordered transition-elements being separate from, and not part of, the object or a data structure of the object;

(b) a reference element for referencing one of the transition elements in said transition vector, and said reference element being accessible in the object;

(c) each of said transition elements including locking means for locking the object and unlocking means for unlocking the object;

(d) said locking means having means for assigning said reference element to the next transition element in response to a locking request for the object by the thread; and

(e) said unlocking means having means for assigning said reference element to the previous element in response to an unlocking request for the object by the thread.

2. The mechanism as claimed in claim 1, further including means for providing a lock count indicative of the number of locks on the object.

3. The mechanism as claimed in claim 1, wherein said transition vector comprises a contiguous array of elements stored in memory.

4. The mechanism as claimed in claim 3, wherein said ordered transition elements comprise an initial transition element, a plurality of shallow-locking transition elements, and a deep locking transition element.

5. The mechanism as claimed in claim 4, wherein said initial transition element is stored in global memory.

6. The mechanism as claimed in claim 5, wherein said shallow-locking transition elements and said deep locking transition element are stored in memory specific to the thread operating on the object.

7. The mechanism as claimed in claim 1, wherein said locking means comprises a locking function and said unlocking means comprises an unlocking function, and said transition element comprises a structure having first and second function pointers, said first function pointer referencing said locking function and said second function pointer referencing said unlocking function.

8. The mechanism as claimed in claim 1, further including casting means for changing the transition vector assigned to said object, said casting means comprising means for modifying said reference element wherein said reference element references a transition element in another transition vector.

9. The mechanism as claimed in claim 8, wherein said first transition vector comprises a transition vector for structured locking and unlocking of the object, and said second transition vector comprises a transition vector for unstructured locking and unlocking.

10. The mechanism as claimed in claim 1, further including plumbing means for modifying said locking means or said unlocking means in one of said transition elements.

11. The mechanism as claimed in claim 1, further including cross-thread casting means for changing the transition vector assigned to said object to a transition vector in another thread, said cross-thread casting means comprising means for modifying said reference element wherein said reference element references a transition element in the transition vector for said other thread.

12. The mechanism as claimed in claim 1, further including cross-thread plumbing means for modifying locking means or unlocking means in a transition element wherein said transition vector belongs to another thread.

20. The mechanism as claimed in claim 1, wherein said mechanism provides one level of indirection from the object to said locking means and the one level of indirection from the object to said unlocking means, through said reference element.

21. The mechanism as claimed in claim 1, wherein the transition vector includes the plurality of ordered transition elements therein, such that no references exist from the transition vector itself to any of the plurality of ordered transition elements.

23. The mechanism as claimed in claim 1, wherein said means for assigning said reference element to the previous transition element assigns said reference element to the previous transition element in response to the unlocking request for the object by the thread irrespective of a corresponding state of any other objects in a same class as the object.

13. A method for managing the locking and unlocking of an object by a thread, said method utilizing a transition vector comprising an ordered set of transition elements and each of said transition elements comprising a structure having first and second function pointers, said first function pointer referencing a locking function for locking said object and said second function pointer referencing an unlocking function for unlocking said object, said method comprising the steps of:

(a) assigning a transition vector to an object when the object is created, wherein a reference element in the object is assigned to the first transition element in the transition vector;

(b) invoking the locking function in the currently referenced transition element in response to a request from the thread to lock the object, and assigning said reference element to the next transition element in the transition vector;

(c) invoking the unlocking function in the currently assigned transition element in response to a request from the thread to unlock the object, and assigning said reference element to the previous transition element in the transition vector;

(d) generating an exception in step (c) if a request is made by a thread to unlock an object which has not been locked, wherein each of the transition elements in the ordered set of transition elements is separate from, and not part of, the object or a data structure of the object.

14. The method as claimed in claim 13, further including steps for invoking a deep locking function when the lock requests for the object exceed a lock threshold.

15. The method as claimed in claim 13, further including steps for changing the transition vector assigned to the object comprising assigning the reference element in said object to a transition element in another transition vector so that said reference element references said other transition vector.

16. The method as claimed in claim 13, wherein said first transition vector is utilized for structured locking and unlocking of the object and said second transition vector is utilized for unstructured locking and unlocking of the object.

17. The method as claimed in claim 13, further including steps for modifying said locking and unlocking functions in one or more of said transition elements.

18. The method as claimed in claim 13, further including steps for modifying said locking and unlocking functions in one or more said transition elements, wherein said transition elements belong to a transition vector assigned to an object in another thread.

19. The method according to claim 13, wherein said method is implemented by a program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform said method steps.

22. The method as claimed in claim 13, wherein the transition vector comprises the ordered set of transition elements therein, such that no references exist from the transition vector itself to any of the transition elements in the ordered set of transition elements.