Lightweight Single Reader Locks

• US 20080040560A1
• Filed: 03/15/2007
• Published: 02/14/2008
• Est. Priority Date: 03/16/2006
• Status: Abandoned Application

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Wang, Zhong Liang, Hall, Charles Brian
• Application Number:
  US11/686,498
• Publication Number:
  US 20080040560A1
• Time in Patent Office: Days
• US Class Current: 711/152
• CPC Class Codes: G06F 2209/523 Mode
• 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 9/526 Mutual exclusion algorithms

Abstract

A method, system and computer program product for generating a read-only lock implementation from a read-only lock portion of program code. In response to determining that a lock portion of the program code is a read-only lock, a read-only lock implementation is generated to protect at least one piece of shared data. The read-only lock implementation comprises a plurality of instructions with dependencies created between the instructions to ensure that a lock corresponding to the data is determined to be free before permitting access to that data. In one embodiment, when executed, the read-only lock implementation loads a lock word from a memory address into a register and places a reserve on the memory address. The lock word is evaluated to determine if the lock is free, and, in response to determining that the lock is tree, at least one piece of shared data protected by the lock is accessed. A value is conditionally stored back to the memory address if the reserve is present. A dependency exists between the step of loading of the lock word and the step of accessing the at least one piece of shared data, thereby causing the step of loading of the lock word to be performed before the step of accessing of the at least one piece of shared data.

Claims

1. A computer-implementable method of generating a read-only lock implementation from a read-only lock portion of a program code, comprising:

in response to determining that a lock portion of the program code is a read-only lock, generating a read-only lock implementation to protect at least one piece of shared data wherein the read-only lock implementation comprises a plurality of instructions with dependencies created between the instructions to ensure that a lock corresponding to the at least one piece of shared data is determined to be free before permitting access to the at least one piece of shared data,

2. The method of claim 1 wherein the read-only lock implementation, when executed by a data processing system, causes the data processing system to perform the following steps:

loading a lock word from a memory address into a register and placing a reserve on the memory address;

responsive to loading the lock word, evaluating the lock word to determine if the lock is free;

responsive to determining that the lock is free, accessing one or more of the at least one piece of shared data; and

conditionally storing a value back to the memory address if the reserve is present,

wherein a dependency exists between the step of loading of the lock word and the step of accessing the one or more of the at least one piece of shared data, thereby causing the data processing system to perform the loading of the lock word before the data processing system performs the accessing of the one or more of the at least one piece of shared data.

3. The method of claim 2 wherein the method uses at least one additional instruction to create the dependency between the step of loading of the lock word and the step of accessing the one or more of the at least one piece of shared data.

4. The method of claim 3 wherein the at least one additional instruction performs an operation on values that leaves the values unaltered.

5. The method of claim 1 wherein the method is carried out when the program code is compiled.

6. The method of claim 1 wherein the program code is Java bytecode

7. A computer-implementable method of performing a read-only lock on at least one piece of shared data, the method comprising:

loading a lock word from a memory address into a register and placing a reserve on the memory address;

responsive to loading the lock word, evaluating the lock word to determine if the lock is free;

responsive to determining that the lock is free, accessing at least one piece of shared data protected by the lock; and

conditionally storing a value back to the memory address if the reserve is present,

wherein dependencies created between the steps cause the step of evaluating the lock word to determine if the lock is free to be performed prior to accessing the at least one piece of shared data.

8. The method of claim 7 wherein at least one dependency is created between steps by an additional instruction.

9. A multi-threaded data processing system for generating a read-only lock implementation from a read-only lock portion of a program code, comprising:

at least one processor;

a memory operatively coupled to the at least one processor; and

a program module stored in the memory operative for providing instructions to the at least one processor, the at least one processor responsive to the instructions from the program module to cause the data processing system to;

in response to determining that a lock portion of a program code is a read-only lock, generate a read-only lock implementation to protect at least one piece of shared data wherein the read-only lock implementation comprises a plurality of instructions with dependencies created between the instructions to ensure that a lock corresponding to the at least one piece of shared data is determined to be free before permitting access to the at least one piece of shared data.

10. The data processing system of claim 9 wherein the read-only lock implementation, when executed by the data processing system, causes the data processing system to execute the following steps:

loading a lock word from a memory address into a register and placing a reserve on the memory address;

responsive to loading the lock word, evaluating the lock word to determine if the lock is free;

responsive to determining that the lock is free, accessing one or more of the at least one piece of shared data; and

conditionally storing a value back to the memory address if the reserve is present,

wherein a dependency exists between the step of loading of the lock word and the step of accessing the one or more of the at least one piece of shared data, thereby causing the data processing system to perform the loading of the lock word before the data processing system performs the accessing of the one or more of the at least one piece of shared data.

11. The data processing system of claim 10 wherein the method uses at least one additional instruction to create the dependency between the step of loading of the lock word and the step of accessing the one or more of the at least one piece of shared data.

12. The data processing system of claim 11 wherein the at least one additional instruction performs an operation on values that leaves the values unaltered.

13. The data processing system of claim 9 wherein the steps are executed when the program code is compiled.

14. The data processing system of claim 9 wherein the program code is Java bytecode.

15. A computer program product comprising a computer useable medium including a computer-readable program for generating a read-only lock implementation from a read-only lock portion of a target program code, wherein the computer-readable program comprises.

computer-readable program code for generating, in response to determining that a lock portion of the target program code is a read-only lock, a read-only lock implementation to protect at least one piece of shared data wherein the read-only lock implementation comprises a plurality of instructions with dependencies created between the instructions to ensure that a lock corresponding to the at least one piece of shared data is free before permitting access to the at least one piece of shared data.

16. The computer program product of claim 15 wherein the read-only lock implementation generated by the computer program product, when executed by a data processing system, causes the data processing system to execute the following steps:

loading a lock word from a memory address into a register and placing a reserve on the memory address;

responsive to loading the lock word, evaluating the lock word to determine if the lock is free;

responsive to determining that the lock is free, accessing one or more of the at least one piece of shared data; and

conditionally storing a value back to the memory address if the reserve is present,

wherein a dependency exists between the step of loading of the lock word and the step of accessing the one or more of the at least one piece of shared data, thereby causing the data processing system to perform the loading of the lock word before the data processing system performs the accessing of the one or more of the at least one piece of shared data,

17. The computer program product of claim 16 wherein the method uses at least one additional instruction to create the dependency between the step of loading of the lock word and the step of accessing the one or more of the at least one piece of shared data.

18. The computer program product of claim 17 wherein the at least one additional instruction performs an operation on values that leaves the values unaltered.

19. The computer program product of claim 15 wherein the method is carried out when the program code is compiled.

20. The computer program product of claim 15 wherein the program code is Java bytecode.