1 © 1999 Citrix Systems Inc

CITRIX

Using type information ingarbage collection

Tim Harris

2 © 1999 Citrix Systems Inc

CITRIXTraditional heap organization

Reg

iste

rsSt

ack

Heap

3 © 1999 Citrix Systems Inc

CITRIXBaker’s treadmill collector

4 © 1999 Citrix Systems Inc

CITRIXProblem : reclamation is very bursty

Time

Hea

p si

ze

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

5 © 1999 Citrix Systems Inc

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?

6 © 1999 Citrix Systems Inc

CITRIXAlternative : use type information

Reg

iste

rsSt

ack

7 © 1999 Citrix Systems Inc

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

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CITRIXSegregating the heap - example 1

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CITRIXSegregating the heap - example 2

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CITRIXSegregating the heap - example 3

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CITRIXImplementation

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CITRIXResults - Delta Blue

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CITRIXResults - Jar

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CITRIXResults - Javac

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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?

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CITRIXNative-code compiler - original

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CITRIXNative-code compiler - revised

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CITRIXFuture work: parametric polymorphism

How are ‘generic’ references handled?

public class List

{

Object data;

List next;

}

public class List<T>

{

T data;

List next;

}