Methods and apparatus for sharing stored data objects in a computer system

• US 5,835,906 A
• Filed: 07/01/1996
• Issued: 11/10/1998
• Est. Priority Date: 07/01/1996
• Status: Expired due to Term

• Current Assignee: Oracle America, Inc. (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Hagersten, Erik E., Hill, Mark Donald
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): HO, RUAY L
• Application Number:
  US08/673,130
• Time in Patent Office: 862 Days
• Field of Search: 395/601, 395/602, 395/603, 395/607, 395/608, 395/609, 395/610, 395/611, 395/616, 395/617, 395/618, 395/619, 395/620, 395/468, 395/823, 395/825, 395/840, 707/1, 707/2, 707/3, 707/7, 707/8, 707/9, 707/10, 707/100
• US Class Current: 707/704
• CPC Class Codes: G06F 9/52 Program synchronisation; Mutual exclusion, e.g. by means of semaphores
• CPC Class Codes: Y10S 707/955 Object-oriented
• CPC Class Codes: Y10S 707/99931 Database or file accessing
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database

Abstract

A method, in a computer system having a first plurality of stored data objects and capable of running multiple threads concurrently, for preventing access conflicts. The method includes the step of providing a dynamic lock structure having a plurality of dynamic lock structure members. There is also the step of mapping a second plurality of stored data objects of the first plurality of stored data objects into a first dynamic lock structure member of the plurality of dynamic lock structure members in accordance with a mapping function. Due to the mapping function, the plurality of dynamic lock structure members become fewer in number than the number of the first plurality of stored data objects. The first dynamic lock structure member is configured to store identities of a third plurality of stored data objects. The third plurality of stored data objects represent a subset of the second plurality of stored data objects that are accessed, whereby a stored data object having its identity stored in the dynamic lock structure cannot be accessed by any thread other than a thread currently accessing the stored data object.

Claims

1. In a computer system having a first plurality of stored data objects and capable of running multiple threads concurrently, an apparatus for preventing access conflicts, said access conflicts arise when more than one of said multiple threads were allowed to simultaneously access one of said first plurality of stored data object, comprising:

a dynamic lock structure having a plurality of dynamic lock structure members that each include a physical lock, said plurality of dynamic lock structure members being fewer in number than a number of said first plurality of stored data objects, wherein a second plurality of stored data objects of said first plurality of stored data objects map into a first dynamic lock structure member of said plurality of dynamic lock structure members in accordance with a mapping function, said mapping function renders it likely that only one stored data object of said second plurality of stored data objects that maps into said first dynamic lock structure member is accessed at any given point in time by a thread of said multiple threads; and

storage facility associated with said first dynamic lock structure member for storing identities of a third plurality of stored data objects, said third plurality of stored data objects represents a subset of said second plurality of stored data objects that are currently being accessed, whereby a stored data object having its identity stored in said dynamic lock structure cannot be accessed by any thread other than a thread currently accessing said stored data object.

2. The apparatus of claim 1 wherein said first dynamic lock structure member comprises a physical lock, said physical lock being configured to store an identity of a first stored data object, said first stored data object representing the only one of said second plurality of stored data objects that is currently accessed.

3. The apparatus of claim 2 wherein said first dynamic lock structure member further comprises a dynamic list for storing said identities of said third plurality of stored data objects if there are at least two stored data objects in said third plurality of stored data objects.

8. The apparatus of claim 3 wherein said first dynamic lock structure member further comprises a link-lock flag, said link-lock flag when set prevents said dynamic list from being accessed for storing additional stored data object identity thereto or for removing previously stored identities of stored data objects therefrom by any other thread except a thread that originally sets said link-lock flag.

4. The apparatus of 3 wherein said physical lock is configured to alternatively store an EMPTY flag if said dynamic list is empty, else said physical lock is configured to alternatively store a NOT_-- EMPTY flag if said dynamic list stores identities of said at least two stored data objects.

5. The apparatus of claim 4 wherein said first dynamic lock structure member is employed by another thread to ascertain whether a given stored data object of said second plurality of stored data object is available for access by said another thread.

6. The apparatus of claim 5 wherein said physical lock is consulted first by said another thread to determine whether said physical lock stores an identity of said given stored data object, said thread being directed to consult said dynamic list if said physical lock stores said NOT_-- EMPTY flag.

7. The apparatus of claim 5 wherein said physical lock is consulted first by said another thread to determine whether said physical lock stores an identity of said given stored data object, said thread being directed to consult said dynamic list if said physical lock stores an identity of a stored data object.

9. In a computer system having a first plurality of stored data objects and capable of running multiple threads concurrently, a method for preventing access conflicts, said access conflicts arise when more than one of said multiple threads were allowed to simultaneously access one of said first plurality of stored data object, comprising:

providing a dynamic lock structure having a plurality of dynamic lock structure members, and each of said plurality of dynamic lock structures includes a physical lock that is configured to alternatively store an EMPTY flag if said dynamic list is empty, else said physical lock is configured to alternatively store a NOT_-- EMPTY flag if said dynamic list stores identities of said at least two stored data objects; and

mapping a second plurality of stored data objects of said first plurality of stored data objects into a first dynamic lock structure member of said plurality of dynamic lock structure members in accordance with a mapping function, thereby resulting in said plurality of dynamic lock structure members being fewer in number than a number of said first plurality of stored data objects, said first dynamic lock structure member being configured to store identities of a third plurality of stored data objects, said third plurality of stored data objects represents a subset of said second plurality of stored data objects that are accessed,

whereby a stored data object having its identity stored in said dynamic lock structure cannot be accessed by any thread other than a thread currently accessing said stored data object.

10. The method of claim 9 wherein said physical lock is associated with said first dynamic lock structure member and configured to store an identity of a first stored data object, said first stored data object representing the only one of said second plurality of stored data objects that is accessed.

11. The method of claim 10 wherein said step of providing a dynamic lock structure further comprising:

providing a dynamic list, said dynamic list being configured to store identities of said third plurality of stored data objects if there are at least two stored data objects in said third plurality of stored data objects.

12. The method of claim 11 wherein said first dynamic lock structure member is configured such that another thread wishing to ascertain whether a given stored data object of said second plurality of stored data object is available for access by said another thread so ascertains by comparing an identity of said given stored data object with identities of stored data objects, if any, stored in said first dynamic lock structure member.

13. The method of claim 12 wherein said first dynamic lock structure member is configured such that said physical lock is consulted first by said another thread to determine whether said physical lock stores said identity of said given stored data object, said thread being directed to consult said dynamic list if said physical lock stores said NOT_-- EMPTY flag.

14. The method of claim 12 wherein said first dynamic lock structure member is configured such that said physical lock is consulted first by said another thread to determine whether said physical lock stores said identity of said given stored data object, said thread being directed to consult said dynamic list if said physical lock stores an identity of a stored data object.

15. The method of claim 11 wherein said step of providing a dynamic lock structure further comprising providing a link-lock flag, said link-lock flag when set prevents said dynamic list from being accessed for storing additional stored data object identity thereto or for removing previously stored identities of stored data objects therefrom by any other thread except a thread that originally sets said link-lock flag.

16. In a computer system having a first plurality of stored data objects and capable of running a first thread and a second thread concurrently, a method for preventing an access conflict, said access conflict arises if said first and second threads were allowed to simultaneously access a first stored data object of said first plurality of stored data object, said computer system having a dynamic lock structure including a dynamic lock structure member, a second plurality of stored data objects of said first plurality of stored data objects, including said first stored data object being mapped into said first dynamic lock structure member, said first dynamic lock structure member being configured to store identities of a third plurality of stored data objects, said third plurality of stored data objects represents a subset of said second plurality of stored data objects that are accessed, whereby a stored data object having its identity stored in said dynamic lock structure cannot be accessed by any thread other than a thread currently accessing said stored data object, comprising:

facilitating an attempted access by said first thread to said first stored data object, including;

if said dynamic lock structure member does not store any stored data object identity, storing an identity of said first stored data object into a physical lock portion of said dynamic lock structure;

else if said dynamic lock structure member stores only one identity of a second stored data object in said physical lock portion, said second stored data object being different from said first stored data object, storing both said identity of said first stored data object and said identity of said second stored data object into a dynamic list portion of said dynamic lock structure and storing a first flag into said physical lock portion of said dynamic lock structure, said first flag indicating that said dynamic list is currently not empty;

else if said dynamic lock structure member stores only one identity of a second stored data object, said second stored data object is the same as said first stored data object, rejecting said attempted access by said first thread to said first stored data object as failed;

else if said physical lock stores said first flag indicating that said dynamic list is currently not empty, consulting said dynamic list to ascertain whether said identity of said first data object is already stored in said dynamic list, further including;

rejecting said attempted access by said first thread to said first stored data object as failed if said dynamic list already stores said identity of said first data object; and

else permitting said attempted access by said first thread to said first stored data object if said dynamic list has not already stored said identity of said first data object and storing said identity of said first stored data object into said dynamic list.

17. The method of claim 16 wherein said first thread permits other threads to access said first stored data object when said first thread is finished with accessing said first stored data object by removing said identity of said first stored data object from said physical lock portion of said dynamic lock structure member if said identity of said first stored data object represents the only stored data object identity stored by said dynamic lock structure member.

18. The method of claim 16 wherein said first thread permits other threads to access said first stored data object when said first thread is finished with accessing said first stored data object by removing said identity of said first stored data object from said dynamic list portion of said dynamic lock structure member if said dynamic lock structure member stores a plurality of stored data object identities prior to said removing.

19. The method of claim 18 further comprising the step of moving a remaining stored data object identity from said dynamic list portion to said physical lock portion, said remaining stored data object identity represents the only stored data object identity stored by said dynamic lock structure member after said identity of said first stored data object is removed from said dynamic list portion.

20. In a computer system having a first plurality of stored data objects and capable of running multiple threads concurrently, an apparatus for preventing access conflicts, said access conflicts arise when more than one of said multiple threads were allowed to simultaneously access one of said first plurality of stored data object, comprising:

a dynamic lock structure having a plurality of dynamic lock structure members, said plurality of dynamic lock structure members being fewer in number than a number of said first plurality of stored data objects, wherein a second plurality of stored data objects of said first plurality of stored data objects map into a first dynamic lock structure member of said plurality of dynamic lock structure members in accordance with a mapping function, said mapping function renders it likely that only one stored data object of said second plurality of stored data objects that maps into said first dynamic lock structure member is accessed at any given point in time by a thread of said multiple threads; and

storage facility having a physical lock, a list lock flag and a dynamic list, said storage facility is associated with said first dynamic lock structure member and is configured to store identities of a third plurality of stored data objects, said third plurality of stored data objects represents a subset of said second plurality of stored data objects that are currently being accessed;

wherein a stored data object having its identity stored in said dynamic lock structure cannot be accessed by any thread other than a thread currently accessing said stored data object.

21. The apparatus of claim 20 wherein said physical lock is configured to store an identity of a first stored data object, said first stored data object representing the only one of said second plurality of stored data objects that is currently accessed.

22. The apparatus of claim 21 wherein said dynamic list is used for storing said identities of said third plurality of stored data objects if there are at least two stored data objects in said third plurality of stored data objects.

23. The apparatus of 22 wherein said physical lock is configured to alternatively store an EMPTY flag if said dynamic list is empty, else said physical lock is configured to alternatively store a NOT_-- EMPTY flag if said dynamic list stores identities of said at least two stored data objects.

24. In a computer system having a first plurality of stored data objects and capable of running multiple threads concurrently, a method for preventing access conflicts, said access conflicts arise when more than one of said multiple threads were allowed to simultaneously access one of said first plurality of stored data object, comprising:

providing a dynamic lock structure having a plurality of dynamic lock structure members, where each of said plurality of dynamic lock structure members has a physical lock that is configured to store an identity of a first stored data object, said first stored data object representing the only one of said second plurality of stored data objects that is accessed; and

mapping a second plurality of stored data objects of said first plurality of stored data objects into a first dynamic lock structure member of said plurality of dynamic lock structure members in accordance with a mapping function, thereby resulting in said plurality of dynamic lock structure members being fewer in number than a number of said first plurality of stored data objects, said first dynamic lock structure member being configured to store identities of a third plurality of stored data objects, said third plurality of stored data objects represents a subset of said second plurality of stored data objects that are accessed,

wherein a stored data object having its identity stored in said dynamic lock structure cannot be accessed by any thread other than a thread currently accessing said stored data object.

25. The method of claim 24 wherein said providing a dynamic lock structure further comprising:

providing a dynamic list, said dynamic list is configured to store identities of said third plurality of stored data objects if there are at least two stored data objects in said third plurality of stored data objects.