1 © 1999 Citrix Systems Inc Using type information in garbage collection Tim Harris

1 © 1999 Citrix Systems Inc

CITRIX

Using type information ingarbage collection

Tim Harris


CITRIXTraditional heap organization

Reg

iste

rsSt

ack

Heap


CITRIXBaker’s treadmill collector


CITRIXProblem : reclamation is very bursty

Time

Hea

p si

ze

The whole heap has to be checked before any storage can be reclaimed.


CITRIXGenerational collection

Idea: separate newly created objects Evidence that they are likely to soon become garbage

Scan and reclaim space used by new objects without examining the entire heap How are references from old to new objects handled? When does an object become ‘old’?

How else could the heap be divided?


CITRIXAlternative : use type information

Reg

iste

rsSt

ack


CITRIXPotential benefits

Some storage can be reclaimed after each section of the heap has been scanned

Different sections can be scanned with different algorithms and maybe concurrently by different threads

Some sections can be scanned more frequently than others


CITRIXSegregating the heap - example 1






CITRIXImplementation


CITRIXResults - Delta Blue


CITRIXResults - Jar


CITRIXResults - Javac


CITRIXRemaining problems

Can new class definitions be handled efficiently at run-time?

Can the classes for non-trivial applications be effectively divided into these sections?

How is the success of the approach affected by different programming styles?


CITRIXNative-code compiler - original


CITRIXNative-code compiler - revised


CITRIXFuture work: parametric polymorphism

How are ‘generic’ references handled?

public class List

{

Object data;

List next;

}

public class List<T>

{

T data;

List next;

}

Documents

1 © 1999 Citrix Systems Inc Using type information in garbage collection Tim Harris