Extended garbage collection

• US 20090030958A1
• Filed: 07/25/2007
• Published: 01/29/2009
• Est. Priority Date: 07/25/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Garst, Gerald Blaine JR.
• Granted Patent: US 8,504,596 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 12/0269 Incremental or concurrent garbage collection, e.g. in real-time systems G06F12/0261 takes precedence

Abstract

Extended garbage collection is disclosed. It is determined, based at least in part on data stored in a data structure accessible to the respective garbage collecting entity of each of a plurality of runtime systems, that a local object is associated with one or more external objects. The local object is retained, even if the local object has been determine to be unreachable locally in a local runtime system with which the local object is associated, if at least one of said one or more external objects has been determined to be reachable within an external runtime environment with which the at least one external object is associated.

Claims

1. A method of managing memory, comprising:

determining, based at least in part on data stored in a data structure accessible to the respective garbage collecting entity of each of a plurality of runtime systems, that a local object is associated with one or more external objects; and

retaining the local object, even if the local object has been determine to be unreachable locally in a local runtime system with which the local object is associated, if at least one of said one or more external objects has been determined to be reachable within an external runtime environment with which the at least one external object is associated.

2. A method as recited in claim 1, wherein the determination that the local object is associated with one or more external objects is made by a local garbage collecting entity associated with the local runtime system.

3. A method as recited in claim 1, wherein determining that the local object is associated with one or more external objects includes scanning the data structure for an entry associated with the local object.

4. A method as recited in claim 1, wherein the data structure accessible to the respective garbage collecting entity of each of a plurality of runtime systems comprises a table.

5. A method as recited in claim 1, wherein the determination that the at least one of said one or more external objects is reachable within the external runtime environment with which the at least one external object is associated is made by an external garbage collecting entity associated with the external runtime environment with which the at least one external object is associated.

6. A method as recited in claim 1, wherein the local object and the one or more external objects comprises a distributed object.

7. A method as recited in claim 6, wherein the distribute object comprises a single component object in each of a plurality of runtime systems.

8. A method as recited in claim 1, further comprising receiving an indication that the local object is associated with the one or more external objects and storing in the data structure an entry indicating that the local object and the one or more external objects are associated with one another.

9. A method as recited in claim 8, wherein receiving an indication comprises receiving from an application code a call to a method or function configured to make, in response to the call, said entry indicating that the local object and the one or more external objects are associated with one another.

10. A method as recited in claim 1, further comprising determining that the local object is reachable within the local runtime system and entering in the data structure a data value that marks the local object as having been determined to be reachable within the local runtime system.

11. A method as recited in claim 1, further comprising receiving an indication that the local object has sent and inter-runtime system message to the at least one of said one or more external objects and entering in the data structure a data value that marks the at least one of said one or more external objects as having been determined to be in use.

12. A method as recited in claim 11, wherein the data value comprises a bit that is also used to mark an object as having been determined to be reachable within its runtime system.

13. A method as recited in claim 1, further comprising retaining one or more other local objects, if any, that are determined to be reachable from the local object within the local runtime system.

14. A method as recited in claim 13, wherein said one or more other objects, if any, are retained even if one or more of them have been determined to be otherwise not reachable within the local runtime system.

17. A method as recited in claim 1, further comprising garbage collecting the local object if it is determined that none of the one or more external objects has been determined to be reachable within an external runtime environment with which the external object is associated.

15. A method of managing memory, comprising:

determining that a local object is not reachable within a local runtime system with which the local object is associated; and

retaining the local object if it is determined that the local object is associated with one or more external objects at least one of which has been determined to be reachable within an external runtime system with which it is associated or otherwise still in use.

16. A method as recited in claim 15, wherein the determination that the local object is associated with one or more external objects at least one of which has been determined to be reachable within an external runtime system with which it is associated or otherwise still in use is based at least in part on data stored in a data structure accessible to the respective garbage collecting entity of each of a plurality of runtime systems.

18. A computer system, comprising:

a memory comprising an address space a respective portion of which has been allocated for use as a memory heap by each of a plurality of runtime systems; and

a processor configured to provide each of said plurality of runtime systems, each runtime system including a corresponding garbage collection entity configured to;

determine that a local object is not reachable within a local runtime system with which the local object is associated; and

retain the local object if it is determined that the local object is associated with one or more external objects at least one of which has been determined to be (1) reachable within an external runtime system with which it is associated or (2) otherwise still in use.

19. A computer system as recited in claim 18, wherein each garbage collection entity is configured to make, upon determining that the local object is reachable within the local runtime system, an entry in a data structure accessible to at least a subset of the garbage collection entities indicating that the local object was determined to be reachable.

20. A computer system as recited in claim 18, wherein each garbage collection entity is configured to make, upon determining that the local object is associated with one or more external objects, an entry in a data structure accessible to at least a subset of the garbage collection entities indicating that the local object is associated with the one or more external objects.

21. A computer system as recited in claim 18, wherein the garbage collection entity determines that the local object is associated with an external object if the garbage collection entity receives an indication that the local object has sent an inter-runtime system message to the external object.

22. A computer program product for managing memory, the computer program product being embodied in a computer readable medium and comprising computer instructions for:

determining, based at least in part on data stored in a data structure accessible to the respective garbage collecting entity of each of a plurality of runtime systems, that a local object is associated with one or more external objects; and

retaining the local object, even if the local object has been determine to be unreachable locally in a local runtime system with which the local object is associated, if at least one of said one or more external objects has been determined to be reachable within an external runtime environment with which the at least one external object is associated.