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MCForwardTraceLocal.java
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/
MCForwardTraceLocal.java
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/*
* This file is part of the Jikes RVM project (http://jikesrvm.org).
*
* This file is licensed to You under the Common Public License (CPL);
* You may not use this file except in compliance with the License. You
* may obtain a copy of the License at
*
* http://www.opensource.org/licenses/cpl1.0.php
*
* See the COPYRIGHT.txt file distributed with this work for information
* regarding copyright ownership.
*/
package org.mmtk.plan.markcompact;
import org.mmtk.plan.TraceLocal;
import org.mmtk.plan.Trace;
import org.mmtk.policy.Space;
import org.mmtk.vm.VM;
import org.vmmagic.pragma.*;
import org.vmmagic.unboxed.*;
/**
* This class implments the thread-local functionality for a transitive
* closure over a mark-compact space during the forwarding phase.
*/
@Uninterruptible
public final class MCForwardTraceLocal extends TraceLocal {
/**
* Constructor
*/
public MCForwardTraceLocal(Trace trace) {
super(MC.SCAN_FORWARD, trace);
}
/****************************************************************************
*
* Externally visible Object processing and tracing
*/
/**
* Is the specified object live?
*
* @param object The object.
* @return True if the object is live.
*/
public boolean isLive(ObjectReference object) {
if (object.isNull()) return false;
if (Space.isInSpace(MC.MARK_COMPACT, object)) {
return MC.mcSpace.isLive(object);
}
return super.isLive(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.
*
* In this instance, we refer objects in the mark-sweep space to the
* msSpace for tracing, and defer to the superclass for all others.
*
* @param object The object to be traced.
* @return The new reference to the same object instance.
*/
@Inline
public ObjectReference traceObject(ObjectReference object) {
if (object.isNull()) return object;
if (Space.isInSpace(MC.MARK_COMPACT, object))
return MC.mcSpace.traceForwardObject(this, object);
return super.traceObject(object);
}
/**
* Will this object move from this point on, during the current trace ?
*
* @param object The object to query.
* @return True if the object will not move.
*/
public boolean willNotMoveInCurrentCollection(ObjectReference object) {
return !Space.isInSpace(MC.MARK_COMPACT, object);
}
/**
* Ensure that this object will not move for the rest of the GC.
*
* @param object The object that must not move
* @return The new object, guaranteed stable for the rest of the GC.
*/
@Inline
public ObjectReference precopyObject(ObjectReference object) {
if (VM.VERIFY_ASSERTIONS) {
// All precopying must occur during the initial trace.
VM.assertions._assert(!Space.isInSpace(MC.MARK_COMPACT, object));
}
return super.precopyObject(object);
}
}