Object locks

• US 20060015700A1
• Filed: 07/14/2004
• Published: 01/19/2006
• Est. Priority Date: 07/14/2004
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Burka, Peter W.
• Granted Patent: US 7,447,861 B2
• Time in Patent Office: Days
• US Class Current: 711/163
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

A single lock word comprises an identifier field for storing a thread identifier associated with a first thread obtaining a lock on an object; an inflation field for storing a fat lock bit upon inflation of the lock on the object; and a contention field for storing a contention bit in response to an attempt by a second thread to obtain a lock on the object. The values of the single lock word are verified with a single memory fetch instruction. When unlocking an object, a single memory fetch instruction can be used to read the lock word to: (1) determine whether thread T is still the current owner of the lock, and (2) determine the states of inflation and/or contention (i.e., determine whether the fat lock and/or contention bits have been set).

Claims

1. A method for handling object locks, comprising:

storing a thread identifier associated with a first thread in an identifier field of a lock word upon establishment of a lock on an object by the first thread, wherein the lock word further comprises an inflation field for storing a fat lock bit and a contention field for storing a contention bit; and

verifying the thread identifier stored in the identifier field and determining a state inflation and a state of contention by reading the lock word.

2. The method of claim 1, further comprising releasing the lock on the object by the first thread.

3. The method of claim 1, wherein verifying the thread identifier stored in the identifier field and determining a state inflation and a state of contention by reading the lock word comprises determining whether the fat lock bit has been set in the inflation field and whether the contention bit has been set in the contention field.

4. The method of claim 1, wherein the lock word is read using a single memory fetch instruction.

5. The method of claim 1, further comprising setting the contention bit in the contention field of the lock word in response to an attempt by a second thread to establish a lock on the object.

6. The method of claim 5, further comprising the second thread periodically checking that the contention bit is still set.

7. The method of claim 5, further comprising inflating the lock in response to the setting of the contention bit in the contention field.

8. The method of claim 7, wherein inflating the lock in response to the setting of the contention bit in the contention field comprises storing a monitor identifier in the identifier field and setting the fat lock bit in the inflation field.

9. The method of claim 1, wherein the object is a Java object.

10. A method for handling object locks in a Java Virtual Machine (JVM), comprising:

storing a thread identifier associated with a first thread in an identifier field of a lock word upon establishment of a lock on a Java object by the first thread, wherein the lock word further comprises an inflation field for storing a fat lock bit and a contention field for storing a contention bit;

setting a contention bit in the contention field of the lock word in response to an attempt by a second thread to establish a lock on the Java object;

verifying the thread identifier stored in the identifier field and determining a state of the fat lock bit and the contention bit by reading the lock word;

releasing the lock on the Java object by the first thread; and

inflating the lock in response to determining that the contention bit has been set in the contention field.

11. The method of claim 10, wherein verifying the thread identifier stored in the identifier field and determining a state of the fat lock bit and the contention bit by reading the lock word comprises determining whether the contention bit has been set in the contention field.

12. The method of claim 10, wherein inflating the lock in response to determining that the contention bit has been set in the contention field comprises storing a monitor identifier in the identifier field and setting the fat lock bit in the inflation field.

16. The unitary lock structure of claim 12, wherein the identifier field alternatively stores a monitor identifier upon inflation of the lock on the object.

22. The system of claim 16, wherein the verification system reads the lock word using a single memory fetch instruction.

23. The system of claim 16, wherein the object is a Java object.

13. A unitary lock structure, comprising:

an identifier field for storing a thread identifier associated with a first thread obtaining a lock on an object;

an inflation field for storing a fat lock bit upon inflation of the lock on the object; and

a contention field for storing a contention bit in response to an attempt by a second thread to obtain a lock on the object.

14. The unitary lock structure of claim 13, wherein the unitary lock structure comprises a single lock word.

15. The unitary lock structure of claim 13, wherein the object is a Java object.

17. A system comprising:

a lock engagement system for storing a thread identifier associated with a first thread in an identifier field of a lock word upon establishment of a lock on an object by the first thread, wherein the lock word further comprises an inflation field for storing a fat lock bit and a contention field for storing a contention bit;

a lock contention system for setting the contention bit in response to an attempt by a second thread to establish a lock on the object; and

a verification system for reading the lock word to verify the thread identifier stored in the identifier field and to determine a state of the fat lock bit and the contention bit.

18. The system of claim 17, further comprising a lock word system for generating the lock word.

19. The system of claim 17, further comprising a lock release system for resetting the identifier field upon release of the lock on the object by the first thread if the contention bit has not been set in the contention field.

20. The system of claim 17, further comprising a lock inflation system for inflating the lock upon release of the lock on the object by the first thread if the contention bit has been set in the contention field.

21. The system of claim 20, wherein the lock inflation system inflates the lock by storing a monitor identifier in the monitor field and setting the fat lock bit in the inflation field.

24. A computer program product for handling object locks, the computer program product comprising:

a computer readable medium having computer readable program code embodied therein, the computer readable program code comprising;

computer readable program code configured to store a thread identifier associated with a first thread in an identifier field of a lock word upon establishment of a lock on an object by the first thread, wherein the lock word further comprises an inflation field for storing a fat lock bit and a contention field for storing a contention bit;

computer readable program code configured to set the contention bit in response to an attempt by a second thread to establish a lock on the object; and

computer readable program code configured to read the lock word to verify the thread identifier stored in the identifier field and to determine a state of the fat lock bit and the contention bit.

25. The computer program product of claim 24, further comprising computer readable program code configured to generate the lock word.

26. The computer program product of claim 24, further comprising computer readable program code configured to reset the identifier field upon release of the lock on the object by the first thread if the contention bit has not been set in the contention field.

27. The computer program product of claim 24, further comprising computer readable program code configured to inflate the lock upon the release of the lock on the object by the first thread if the contention bit has been set in the contention field.

28. The computer program product of claim 26, wherein the computer readable program code configured to inflate the lock upon the release of the lock on the object by the first thread if the contention bit has been set in the contention field computer readable program code configured to inflate the lock by storing a monitor identifier in the monitor field and setting the fat lock bit in the inflation field.

29. The computer program product of claim 24, wherein the computer readable program code configured to read the lock word to verify the thread identifier stored in the identifier field and to determine a state of the fat lock bit and the contention bit reads the lock word using a single memory fetch instruction.

30. The computer program product of claim 24, wherein the object is a Java object.

31. A system for deploying an application, comprising:

a computer infrastructure being operable to;

store a thread identifier associated with a first thread in an identifier field of a lock word upon establishment of a lock on an object by the first thread, wherein the lock word further comprises an inflation field for storing a fat lock bit and a contention field for storing a contention bit;

set the contention in response to an attempt by a second thread to establish a lock on the object; and

verify the thread identifier stored in the identifier field and determine a state of the fat lock bit and the contention bit by reading the lock word.

32. The system of claim 31, wherein the lock word is read using a single memory fetch instruction.

33. Computer software embodied in a propagated signal, the computer software comprising instructions to cause a computer system to perform the following functions:

store a thread identifier associated with a first thread in an identifier field of a lock word upon establishment of a lock on an object by the first thread, wherein the lock word further comprises an inflation field for storing a fat lock bit and a contention field for storing a contention bit;

set the contention bit in response to an attempt by a second thread to establish a lock on the object; and

verify the thread identifier stored in the identifier field and determine a state of the fat lock bit and the contention bit by reading the lock word.

34. The computer software of claim 33, wherein the lock word is read using a single memory fetch instruction