Subordinate Multiobjects

1 . A method of managing memory in a data processing device comprising a reference creator, the method comprising:

identifying at least one object with a new reference, said object being within an existing multiobject but not the root of that multiobject; and

creating at least one attached subordinate multiobject whose root object is said object and whose containing multiobject is said existing multiobject.

2 . The method of claim 1 , further comprising:

representing said attached subordinate using a data structure, the data structure comprising at least information from which the address of said object can be determined.

3 . The method of claim 1 , further comprising:

when creating an attached subordinate multiobject:

determining the address range of the subtree rooted at said object; and

reparenting at least one subordinate multiobject within the address range.

4 . The method of claim 1 , further comprising:

when an attached subordinate multiobject is created, marking that its address range has not yet been computed;

when the address range of the subordinate multiobject is first needed:

determining the address range of the subtree rooted at said object; and

reparenting at least one subordinate multiobject within the address range;

thereby avoiding determining of the address range of the multiobject and reparenting the at least one subordinate multiobject if the newly created multiobject is freed before they are needed.

5 . The method of claim 1 , further comprising:

determining the address range of the subtree rooted at said object; and

moving exits in the address range to the created attached subordinate multiobject.

6 . The method of claim 1 , further comprising:

at the end of a transitive closure computation, freeing at least one attached subordinate multiobject that is no longer reachable.

7 . The method of claim 1 , further comprising:

freeing at least one attached subordinate multiobject when its list of exits referencing it becomes empty.

8 . The method of claim 1 , further comprising:

at the end of an evacuation pause, freeing at least one attached subordinate multiobject that is only referenced from transient exits in addition to the implied reference from its containing multiobject.

9 . The method of claim 1 , further comprising:

freeing a subordinate multiobject when its reference count becomes zero.

10 . The method of claim 1 , further comprising:

when the containing multiobject of a first subordinate multiobject is freed, if the containing multiobject is a top-level multiobject, promoting the first subordinate multiobject to a top-level multiobject.

11 . The method of claim 1 , further comprising:

when the containing multiobject of a first subordinate multiobject is freed, if the containing multiobject is a detached subordinate multiobject and the first subordinate multiobject is an attached subordinate multiobject, promoting the first subordinate multiobject to be a detached subordinate multiobject.

12 . The method of claim 1 , further comprising:

when a write occurs to a pointer cell that contains an internal pointer:

determining the address range of the object pointed to by the old value of that cell; and

promoting at least one attached subordinate multiobject within such address range to be a detached subordinate multiobject.

13 . The method of claim 1 , further comprising:

if a transitive closure computation is running when a multiobject is promoted, causing the multiobject computation to visit the promoted multiobject.

14 . The method of claim 1 , further comprising:

computing a transitive closure of the multiobject graph; and

when a multiobject is deemed reachable during the transitive closure computation, causing any attached subordinate multiobject directly contained in it to be deemed as reachable.

15 . The method of claim 1 , further comprising:

when moving a containing multiobject, moving at least one subordinate multiobject along with the containing multiobject.

16 . The method of claim 15 , further comprising:

updating pointers referring to said at least one subordinate multiobject to point to the new location of said at least one subordinate multiobject.

17 . The method of claim 1 , further comprising:

buffering writes during mutator execution using a write barrier buffer such that for each written address the old value of the written cell is saved;

when processing write barrier buffers, for at least one written cell:

creating an attached subordinate multiobject for the new value of the written cell;

determining the address range of the subtree rooted at the object pointed to by the old value of the written cell; and

promoting at least one attached subordinate multiobject within the address range.

18 . The method of claim 1 , further characterized by each subordinate multiobject being properly nested within its containing multiobject.

19 . A data processing device comprising:

at least one nursery memory area comprising objects that have not yet been grouped into multiobjects;

at least one multiobject space comprising one or more top-level multiobjects, at least one of which has been constructed from objects in the nursery memory area;

a reference creator; and

at least one attached subordinate multiobject whose data is stored within the address range of one of the top-level multiobjects, said multiobject having been created by the reference creator.

20 . The data processing device of claim 19 , further comprising at least one detached subordinate multiobject contained within the address range of one of the top-level multiobjects.

21 . The data processing device of claim 19 , further comprising a data barrier buffer for recording writes that occur to within multiobjects, the buffer capable of storing the address and the old value of at least one written cell.

22 . The data processing device of claim 19 , further comprising at least one subtree address range determinator.

23 . The data processing device of claim 19 , further comprising at least one reference creator.

24 . The data processing device of claim 19 , further comprising at least one promoter.

25 . A computer program product operable to cause a data processing device to:

comprise a reference creator;

identify at least one object with a new reference, said object being within an existing multiobject but not the root of that multiobject; and

create at least one attached subordinate multiobject whose root object is said object and whose containing multiobject is the multiobject that contains said object.