org.jikesrvm.mm.mmtk

Class Scanning

java.lang.Object

org.mmtk.vm.Scanning

org.jikesrvm.mm.mmtk.Scanning

public final class Scanning
extends Scanning

Field Summary

Fields

Modifier and Type	Field and Description
private static SynchronizedCounter	threadCounter Counter to track index into thread table for root tracing.

Constructor Summary

Constructors

Constructor and Description
Scanning()

Method Summary

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

Methods inherited from class java.lang.Object

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

Field Detail

threadCounter

private static final SynchronizedCounter threadCounter

Counter to track index into thread table for root tracing.

Constructor Detail

Scanning

public Scanning()

Method Detail

scanObject

public void scanObject(TransitiveClosure trace,
                       ObjectReference object)

Scanning of a object, processing each pointer field encountered.

Specified by:

scanObject in class Scanning

Parameters:

trace - The closure being used.

object - The object to be scanned.

specializedScanObject

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

Description copied from class: Scanning

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

Specified by:

specializedScanObject in class Scanning

Parameters:

id - The specialized method id

trace - The trace the method has been specialized for

object - The object to be scanned

resetThreadCounter

public void resetThreadCounter()

Description copied from class: Scanning

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).

Specified by:

resetThreadCounter in class Scanning

notifyInitialThreadScanComplete

public void notifyInitialThreadScanComplete(boolean partialScan)

Description copied from class: Scanning

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.

Specified by:

notifyInitialThreadScanComplete in class Scanning

Parameters:

partialScan - whether the scan was partial or full-heap

computeStaticRoots

public 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:

• The threadCounter must be reset so that load balancing parallel GC can share the work of scanning threads.

Specified by:

computeStaticRoots in class Scanning

Parameters:

trace - The trace to use for computing roots.

computeGlobalRoots

public 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:

• The threadCounter must be reset so that load balancing parallel GC can share the work of scanning threads.

Specified by:

computeGlobalRoots in class Scanning

Parameters:

trace - The trace to use for computing roots.

computeThreadRoots

public 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.

Specified by:

computeThreadRoots in class Scanning

Parameters:

trace - The trace to use for computing roots.

computeNewThreadRoots

public 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.

Specified by:

computeNewThreadRoots in class Scanning

Parameters:

trace - The trace to use for computing roots.

computeThreadRoots

private void computeThreadRoots(TraceLocal trace,
                                boolean newRootsSufficient)

Compute roots pointed to by threads.

Parameters:

trace - The trace to use for computing roots.

newRootsSufficient - True if it sufficient for this method to only compute those roots that are new since the previous stack scan. If false then all roots must be computed (both new and preexisting).

computeBootImageRoots

public void computeBootImageRoots(TraceLocal trace)

Description copied from class: Scanning

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.

Specified by:

computeBootImageRoots in class Scanning

Parameters:

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

supportsReturnBarrier

public boolean supportsReturnBarrier()

Specified by:

supportsReturnBarrier in class Scanning

Returns:

true if the runtime supports a return barrier