org.mmtk.plan

Class TraceLocal

java.lang.Object

org.mmtk.plan.TransitiveClosure

org.mmtk.plan.TraceLocal

Direct Known Subclasses:

BTTraceLocal, CMSTraceLocal, CopyMSTraceLocal, GenMatureTraceLocal, GenNurseryTraceLocal, GenRCFindRootSetTraceLocal, ImmixDefragTraceLocal, ImmixTraceLocal, MCForwardTraceLocal, MCMarkTraceLocal, MSTraceLocal, NoGCTraceLocal, RCFindRootSetTraceLocal, SanityRootTraceLocal, SanityTraceLocal, SSTraceLocal, StickyImmixNurseryTraceLocal, StickyMSNurseryTraceLocal

public abstract class TraceLocal
extends TransitiveClosure

This abstract class and its global counterpart implement the core functionality for a transitive closure over the heap graph. This class specifically implements the unsynchronized thread-local component (ie the 'fast path') of the trace mechanism.

See Also:

Plan, Trace

Field Summary

Fields

Modifier and Type	Field and Description
protected AddressDeque	rootLocations delayed root slots
protected ObjectReferenceDeque	values gray objects

Fields inherited from class org.mmtk.plan.TransitiveClosure

specializedScan

Constructor Summary

Constructors

Constructor and Description
TraceLocal(int specializedScan, Trace trace) Constructor
TraceLocal(Trace trace) Constructor

Method Summary

Modifier and Type	Method and Description
private void	assertMutatorRemsetsFlushed() Assert that the remsets have been flushed.
void	completeTrace() Finishing processing all GC work.
void	flush() Flush the local buffers of all deques.
ObjectReference	getForwardedFinalizable(ObjectReference object) If a Finalizable object has moved, return the new location.
ObjectReference	getForwardedReference(ObjectReference object) If the referenced object has moved, return the new location.
ObjectReference	getForwardedReferenceType(ObjectReference object) If the Reference Type object has moved, return the new location.
ObjectReference	getForwardedReferent(ObjectReference object) If the reference object (from a Reference Type) has object has moved, return the new location.
boolean	incrementalTrace(int workLimit) Process GC work until either complete or workLimit units of work are completed.
boolean	isLive(ObjectReference object) Is the specified object live?
boolean	isReachable(ObjectReference object) Is the specified object reachable?
boolean	isReferentLive(ObjectReference object) Is the specified referent of a reference type object live?
protected void	logMessage(int minVerbose, String message) This method logs a message with prepended thread id, if the verbosity level is greater or equal to the passed level.
protected boolean	overwriteReferenceDuringTrace()
void	prepare() TODO write JavaDoc comment
void	processEdge(ObjectReference source, Address slot) Trace a reference during GC.
void	processInteriorEdge(ObjectReference target, Address slot, boolean root) Trace a reference during GC.
void	processNode(ObjectReference object) Add a gray object
protected void	processRememberedSets() Flush any remembered sets pertaining to the current collection.
void	processRootEdge(Address slot, boolean untraced) Trace a reference during GC.
void	processRoots() Process any roots for which processing was delayed.
boolean	readyToFinalize(ObjectReference object) Return true if an object is ready to move to the finalizable queue, i.e. it has no regular references to it.
void	release()
void	reportDelayedRootEdge(Address slot) Report a root edge to be processed during GC.
ObjectReference	retainForFinalize(ObjectReference object) An object is unreachable and is about to be added to the finalizable queue.
ObjectReference	retainReferent(ObjectReference object) Make alive a referent object that is known not to be live (isLive is false).
protected void	scanObject(ObjectReference object) Collectors that move objects must override this method.
ObjectReference	traceObject(ObjectReference object) This method is the core method during the trace of the object graph.
ObjectReference	traceObject(ObjectReference object, boolean root) This method traces an object with knowledge of the fact that object is a root or not.
boolean	willNotMoveInCurrentCollection(ObjectReference object) Ensure that the referenced object will not move from this point through to the end of the collection.

Methods inherited from class org.mmtk.plan.TransitiveClosure

getSpecializedScanClass, registerSpecializedScan

Methods inherited from class java.lang.Object

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

Field Detail

values

protected final ObjectReferenceDeque values

gray objects

rootLocations

protected final AddressDeque rootLocations

delayed root slots

Constructor Detail

TraceLocal

public TraceLocal(Trace trace)

Constructor

Parameters:

trace - The global trace class to use.

TraceLocal

public TraceLocal(int specializedScan,
                  Trace trace)

Constructor

Parameters:

specializedScan - The specialized scan id.

trace - The global trace class to use.

Method Detail

overwriteReferenceDuringTrace

protected boolean overwriteReferenceDuringTrace()

Returns:

whether reference values should be overwritten as the heap is traced

processEdge

public final void processEdge(ObjectReference source,
                              Address slot)

Trace a reference during GC. This involves determining which collection policy applies and calling the appropriate trace method.

Overrides:

processEdge in class TransitiveClosure

Parameters:

source - The source of the reference.

slot - The location containing the object reference to be traced. The object reference is NOT an interior pointer.

reportDelayedRootEdge

public final void reportDelayedRootEdge(Address slot)

Report a root edge to be processed during GC. As the given reference may theoretically point to an object required during root scanning, the caller has requested processing be delayed. NOTE: delayed roots are assumed to be raw.

Parameters:

slot - The location containing the object reference to be traced. The object reference is NOT an interior pointer.

processRootEdge

public final void processRootEdge(Address slot,
                                  boolean untraced)

Trace a reference during GC. This involves determining which collection policy applies and calling the appropriate trace method.

Parameters:

slot - The location containing the object reference to be traced. The object reference is NOT an interior pointer.

untraced - true if objLoc is an untraced root.

processInteriorEdge

public final void processInteriorEdge(ObjectReference target,
                                      Address slot,
                                      boolean root)

Trace a reference during GC. This involves determining which collection policy applies and calling the appropriate trace method.

Parameters:

target - The object the interior edge points within.

slot - The location of the interior edge.

root - true if this is a root edge.

scanObject

protected void scanObject(ObjectReference object)

Collectors that move objects must override this method. It performs the deferred scanning of objects which are forwarded during bootstrap of each copying collection. Because of the complexities of the collection bootstrap (such objects are generally themselves gc-critical), the forwarding and scanning of the objects must be dislocated. It is an error for a non-moving collector to call this method.

Parameters:

object - The forwarded object to be scanned

processNode

public final void processNode(ObjectReference object)

Add a gray object

Overrides:

processNode in class TransitiveClosure

Parameters:

object - The object to be enqueued

flush

public final void flush()

Flush the local buffers of all deques.

isLive

public boolean isLive(ObjectReference object)

Is the specified object live?

Parameters:

object - The object.

Returns:

true if the object is live.

isReachable

public boolean isReachable(ObjectReference object)

Is the specified object reachable? Used for GC Trace

Parameters:

object - The object.

Returns:

true if the object is live.

isReferentLive

public boolean isReferentLive(ObjectReference object)

Is the specified referent of a reference type object live?

Parameters:

object - The object.

Returns:

true if the reference object is live.

traceObject

public ObjectReference traceObject(ObjectReference object)

This method is the core method during the trace of the object graph. The role of this method is to:

1. Ensure the traced object is not collected.
2. If this is the first visit to the object enqueue it to be scanned.
3. Return the forwarded reference to the object.

Parameters:

object - The object to be traced.

Returns:

The new reference to the same object instance.

traceObject

public ObjectReference traceObject(ObjectReference object,
                                   boolean root)

This method traces an object with knowledge of the fact that object is a root or not. In simple collectors the fact it is a root is not important so this is the default implementation given here.

Parameters:

object - The object to be traced.

root - Is this object a root?

Returns:

The new reference to the same object instance.

willNotMoveInCurrentCollection

public boolean willNotMoveInCurrentCollection(ObjectReference object)

Ensure that the referenced object will not move from this point through to the end of the collection. This can involve forwarding the object if necessary. Non-copying collectors do nothing, copying collectors must override this method in each of their trace classes.

Parameters:

object - The object that must not move during the collection.

Returns:

true If the object will not move during collection

getForwardedFinalizable

public ObjectReference getForwardedFinalizable(ObjectReference object)

If a Finalizable object has moved, return the new location.

Parameters:

object - The object which may have been forwarded.

Returns:

The new location of object.

getForwardedReferent

public ObjectReference getForwardedReferent(ObjectReference object)

If the reference object (from a Reference Type) has object has moved, return the new location.

Parameters:

object - The object which may have been forwarded.

Returns:

The new location of object.

getForwardedReferenceType

public ObjectReference getForwardedReferenceType(ObjectReference object)

If the Reference Type object has moved, return the new location.

Parameters:

object - The object which may have been forwarded.

Returns:

The new location of object.

getForwardedReference

public ObjectReference getForwardedReference(ObjectReference object)

If the referenced object has moved, return the new location. Some copying collectors will need to override this method.

Parameters:

object - The object which may have been forwarded.

Returns:

The new location of object.

retainReferent

public ObjectReference retainReferent(ObjectReference object)

Make alive a referent object that is known not to be live (isLive is false). This is used by the ReferenceProcessor. For many collectors these semantics reflect those of traceObject, which is implemented here. Other collectors must override this method.

Parameters:

object - The object which is to be made alive.

Returns:

The possibly forwarded address of the object.

retainForFinalize

public ObjectReference retainForFinalize(ObjectReference object)

An object is unreachable and is about to be added to the finalizable queue. The collector must ensure the object is not collected (despite being otherwise unreachable), and should return its forwarded address if keeping the object alive involves forwarding. This is only ever called once for an object.

For many collectors these semantics reflect those of traceObject, which is implemented here. Other collectors must override this method.

TODO is the JavaDoc for this method still up to date?

Parameters:

object - The object which may have been forwarded.

Returns:

The forwarded value for object. In this case return object, copying collectors must override this method.

readyToFinalize

public boolean readyToFinalize(ObjectReference object)

Return true if an object is ready to move to the finalizable queue, i.e. it has no regular references to it. This method may (and in some cases is) be overridden by subclasses. If this method returns true then it can be assumed that retainForFinalize will be called during the current collection. For many collectors these semantics reflect those of isLive, which is implemented here. Other collectors must override this method.

Parameters:

object - The object being queried.

Returns:

true if the object has no regular references to it.

prepare

public void prepare()

TODO write JavaDoc comment

release

public void release()

processRoots

public void processRoots()

Process any roots for which processing was delayed.

completeTrace

public void completeTrace()

Finishing processing all GC work. This method iterates until all work queues are empty.

incrementalTrace

public boolean incrementalTrace(int workLimit)

Process GC work until either complete or workLimit units of work are completed.

Parameters:

workLimit - The maximum units of work to perform.

Returns:

true if all work was completed within workLimit.

processRememberedSets

protected void processRememberedSets()

Flush any remembered sets pertaining to the current collection. Non-generational collectors do nothing.

assertMutatorRemsetsFlushed

private void assertMutatorRemsetsFlushed()

Assert that the remsets have been flushed. This is critical to correctness. We need to maintain the invariant that remset entries do not accrue during GC. If the host JVM generates barrier entries it is its own responsibility to ensure that they are flushed before returning to MMTk.

logMessage

protected final void logMessage(int minVerbose,
                                String message)

This method logs a message with prepended thread id, if the verbosity level is greater or equal to the passed level.

Parameters:

minVerbose - The required verbosity level

message - The message to display