Non-zero null reference to speed up write barrier checking for garbage collection
A method and system of increasing the speed of a write barrier check. Instead of using zero null references, in one embodiment of the invention a special object is created at a valid and globally accessible location in memory. The special object is colored black, and the valid location of the special object is used in objects linked lists, and other elements whenever a null value is required. Preferably, the special object is colored black by coloring a bit pattern in a header of the special object to represent black.
1. A method of increasing the speed of a write barrier check in a computing environment having memory and a plurality of programming objects, the method comprising:
creating a globally accessible special object at a valid location in the memory;
fixing the color of the special object to a predetermined colour; and
using the valid location of the special object whenever a null value is required.
2. A method as claimed in claim 1 , wherein fixing the color of the special object to a predetermined colour includes fixing the color of the special object to black.
3. A method as claimed in claim 2 , wherein fixing the color of the special object to black includes setting a bit pattern in a header of the special object to represent black.
4. A method as claimed in claim 2 , wherein fixing the color of the special object to black includes creating a method that returns black.
5. A method as claimed in claim 2 , further comprising
checking the color of the plurality of programming objects using a write tool; and
assigning references to the objects that are not black.
6. A method as claimed in claim 1 , wherein using the valid location of the special object whenever a null value is required includes using the valid location in a field of an object.
7. A method as claimed in claim 1 , further comprising creating a dispatch table for the special object where every method raises an exception.
8. A method as claimed in claim 2 , further comprising
checking the colour of the plurality of programming objects using a write tool; and
assigning references to the objects that are not black.
9. A method as claimed in claim 1 , further comprising
calling a first subprogram using a programming object;
providing a dispatch table for the special object, the dispatch table having a plurality of entries, each entry referencing a subprogram implementation that raises a run time error unconditionally; and
removing all null object checks from a subprogram call associated with the first subprogram.
10. A write barrier checking apparatus for a computing environment having memory and a plurality of programming objects, the apparatus comprising:
a globally accessible special object having a fixed predetermined color and a valid location in the memory; and
a write tool to check the color of the plurality of objects;
wherein the valid location of the special object is used whenever a null value is required, and the write tool assigns references to the programming objects that are not the predetermined color.
11. An apparatus as claimed in 10 , further comprising a linked list with a plurality of fields, wherein at least one of the fields of the linked list includes the valid location of the special object.
12. An apparatus as claimed in claim 10 , further comprising a dispatch table for the special object.
13. An apparatus as claimed in claim 10 , wherein the predetermined color is black.
14. An apparatus as claimed in claim 13 , wherein the special object includes a header having a bit pattern that represents black.
15. An apparatus as claimed in claim 13 , wherein the special object includes a method that returns black.