org.mmtk.vm

Class Scanning

java.lang.Object

org.mmtk.vm.Scanning

Direct Known Subclasses:

Scanning

public abstract class Scanning
extends Object

Constructor Summary

Constructors

Constructor and Description
Scanning()

Method Summary

Modifier and Type	Method and Description
abstract void	computeBootImageRoots(TraceLocal trace) Compute all roots out of the VM's boot image (if any).
abstract void	computeGlobalRoots(TraceLocal trace) Computes global roots.
abstract void	computeNewThreadRoots(TraceLocal trace) Computes new roots pointed to by threads, their associated registers and stacks.
abstract void	computeStaticRoots(TraceLocal trace) Computes static roots.
abstract void	computeThreadRoots(TraceLocal trace) Computes roots pointed to by threads, their associated registers and stacks.
abstract void	notifyInitialThreadScanComplete(boolean partialScan) Called the first time during a collection that thread's stacks have been scanned.
abstract void	resetThreadCounter() Prepares for using the computeAllRoots method.
abstract void	scanObject(TransitiveClosure trace, ObjectReference object) Delegated scanning of a object, processing each pointer field encountered.
abstract void	specializedScanObject(int id, TransitiveClosure trace, ObjectReference object) Invoke a specialized scan method.
abstract boolean	supportsReturnBarrier()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Scanning

public Scanning()

Method Detail

scanObject

public abstract void scanObject(TransitiveClosure trace,
                                ObjectReference object)

Delegated scanning of a object, processing each pointer field encountered.

Parameters:

trace - the trace to use for scanning

object - The object to be scanned.

specializedScanObject

public abstract void specializedScanObject(int id,
                                           TransitiveClosure trace,
                                           ObjectReference object)

Invoke a specialized scan method. Note that these methods must have been allocated explicitly through Plan and PlanConstraints.

Parameters:

id - The specialized method id

trace - The trace the method has been specialized for

object - The object to be scanned

resetThreadCounter

public abstract void resetThreadCounter()

Prepares for using the computeAllRoots method. The thread counter allows multiple GC threads to co-operatively iterate through the thread data structure (if load balancing parallel GC threads were not important, the thread counter could simply be replaced by a for loop).

notifyInitialThreadScanComplete

public abstract void notifyInitialThreadScanComplete(boolean partialScan)

Called the first time during a collection that thread's stacks have been scanned. This can be used (for example) to clean up obsolete compiled methods that are no longer being executed.

Parameters:

partialScan - whether the scan was partial or full-heap

computeStaticRoots

public abstract void computeStaticRoots(TraceLocal trace)

Computes static roots. This method establishes all such roots for collection and places them in the root locations queue. This method should not have side effects (such as copying or forwarding of objects). There are a number of important preconditions:

• All objects used in the course of GC (such as the GC thread objects) need to be "pre-copied" prior to calling this method.
• The threadCounter must be reset so that load balancing parallel GC can share the work of scanning threads.

Parameters:

trace - The trace to use for computing roots.

computeGlobalRoots

public abstract void computeGlobalRoots(TraceLocal trace)

Computes global roots. This method establishes all such roots for collection and places them in the root locations queue. This method should not have side effects (such as copying or forwarding of objects). There are a number of important preconditions:

• All objects used in the course of GC (such as the GC thread objects) need to be "pre-copied" prior to calling this method.
• The threadCounter must be reset so that load balancing parallel GC can share the work of scanning threads.

Parameters:

trace - The trace to use for computing roots.

computeThreadRoots

public abstract void computeThreadRoots(TraceLocal trace)

Computes roots pointed to by threads, their associated registers and stacks.

This method places these roots in the root values, root locations and interior root locations queues. This method should not have side effects (such as copying or forwarding of objects). There are a number of important preconditions:

• All objects used in the course of GC (such as the GC thread objects) need to be "pre-copied" prior to calling this method.
• The threadCounter must be reset so that load balancing parallel GC can share the work of scanning threads.

Parameters:

trace - The trace to use for computing roots.

computeNewThreadRoots

public abstract void computeNewThreadRoots(TraceLocal trace)

Computes new roots pointed to by threads, their associated registers and stacks. This method is only required to return roots that are new since the last stack scan (if possible, the implementation will optimize the scanning to only scan new portions of the stacks).

This method places these roots in the root values, root locations and interior root locations queues. This method should not have side effects (such as copying or forwarding of objects). There are a number of important preconditions:

• All objects used in the course of GC (such as the GC thread objects) need to be "pre-copied" prior to calling this method.
• The threadCounter must be reset so that load balancing parallel GC can share the work of scanning threads.

Parameters:

trace - The trace to use for computing roots.

computeBootImageRoots

public abstract void computeBootImageRoots(TraceLocal trace)

Compute all roots out of the VM's boot image (if any). This method is a no-op in the case where the VM does not maintain an MMTk-visible Java space. However, when the VM does maintain a space (such as a boot image) which is visible to MMTk, that space could either be scanned by MMTk as part of its transitive closure over the whole heap, or as a (considerable) performance optimization, MMTk could avoid scanning the space if it is aware of all pointers out of that space. This method is used to establish the root set out of the scannable space in the case where such a space exists.

Parameters:

trace - The trace object to use to report root locations.

supportsReturnBarrier

public abstract boolean supportsReturnBarrier()

Returns:

true if the runtime supports a return barrier