PER THREAD GARBAGE COLLECTION

• US 20110238713A1
• Filed: 06/10/2011
• Published: 09/29/2011
• Est. Priority Date: 05/21/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Garst Jr., Gerald Blaine, Beard, Patrick C., Behnke, Douglas Joshua, Parker, Gregory Robert
• Granted Patent: US 8,255,436 B2
• Time in Patent Office: Days
• US Class Current: 707/820
• CPC Class Codes: G06F 12/0253 Garbage collection, i.e. reclamation of unreferenced memory
• CPC Class Codes: G06F 12/0276 Generational garbage collection

Abstract

Per thread garbage collection is disclosed. Objects associated only with a thread that created them are tracked. At a garbage collection time for a particular thread, it is determined which objects associated only with that thread remain reachable from a restricted root set associated with the thread. Any thread-only objects that are not determined to be reachable are garbage collected.

Claims

1. A method for managing memory, comprising:

determining which, if any, objects included in a set of objects associated with a first thread included in a plurality of threads associated with a heap are no longer reachable;

garbage collecting any objects of the set that are not determined to be reachable;

keeping track of which objects stored in the heap are included in the set of objects associated with the first thread; and

removing an object from the set of objects associated with the first thread if the object becomes associated with a thread other than the first thread.

2. The method of claim 1, wherein the set includes only objects not associated with any thread other than first thread.

3. The method of claim 1, wherein the set includes only objects that were created by the first thread and are not referenced, directly or indirectly, by any object not associated with a thread other than the first thread.

4. The method of claim 1, wherein determining includes starting from a reduced root set, traversing objects included in the set of objects associated with the first thread, and marking all objects determined to be reachable directly or indirectly from the reduced root set.

5. The method of claim 4, wherein the reduced root set includes objects comprising a stack associated with the first thread.

6. The method of claim 4, wherein the reduced root set does not include one or more of the following:

global variables and local variables associated with threads other than the first thread.

7. The method of claim 4, wherein garbage collecting includes performing garbage collection processing with respect to any object(s) included in the set of objects associated with the first thread that have not been marked as having been determined to be reachable, directly or indirectly, from the reduced root set.

8. The method of claim 1, wherein keeping track includes allocating and configuring data structure configured to be used to store for each object included in the set data identifying the object.

9. The method of claim 1, wherein keeping track includes storing data indicating an object has been added to the set upon receiving an indication that the object is being or has been created by the first thread.

10. The method of claim 1, wherein the object becomes associated with a thread other than the first thread includes receiving an indication that a reference to the object has been or is being written into an object not included in the set.

11. The method of claim 1, wherein the object becomes associated with a thread other than the first thread includes receiving an indication that a reference to the object has been or is being written to global storage.

12. The method of claim 1, further comprising removing from the set the object and recursively all objects referenced directly or indirectly by the object.

13. The method of claim 1, wherein garbage collecting includes performing finalization processing with respect to an object with respect to which finalization is required.

14. The method of claim 1, wherein garbage collecting includes performing finalization is processing with respect to an object that is referenced by a referencing object with respect to which finalization is required.

15. The method of claim 1, wherein finalization processing is performed, if required, by the first thread.

16. The method of claim 1, further comprising reusing directly one or more memory locations associated with a garbage collected object.

17. The method of claim 16, wherein reusing directly includes considering the one or more memory locations to be available for reuse by the first thread without first returning said one or more memory locations to a shared or other pool.

18. The method of claim 1, further comprising determining that a criteria/on for performing garbage collection with respect to the first thread has/have been met.

19. The method of claim 1, further comprising prompting the first thread to perform said steps of determining and garbage collecting.

20. A computer system, comprising:

a memory comprising a heap with which a plurality of processing threads are associated; and

a processor coupled to the memory and configured to;

determine which, if any, objects included in a set of objects associated with a first thread included in a plurality of threads associated with the heap are no longer reachable;

garbage collect any objects of the set that are not determined to be reachable;

keep track of which objects stored in the heap are included in the set of objects associated with the first thread; and

remove an object from the set of objects associated with the first thread if the object becomes associated with a thread other than the first thread.

21. The computer system of claim 20, wherein the plurality of threads run on the processor.

22. The computer system of claim 20, wherein the first thread is configured to determine which, if any, objects included in the set of objects associated with the first thread are no longer reachable;

and garbage collect any objects of the set that are not determined to be reachable.

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

determining which, if any, objects included in a set of objects associated with a first thread included in a plurality of threads associated with a heap are no longer reachable;

garbage collecting any objects of the set that are not determined to be reachable;

keeping track of which objects stored in the heap are included in the set of objects associated with the first thread; and

removing an object from the set of objects associated with the first thread if the object becomes associated with a thread other than the first thread.