001 /*
002 * This file is part of the Jikes RVM project (http://jikesrvm.org).
003 *
004 * This file is licensed to You under the Eclipse Public License (EPL);
005 * You may not use this file except in compliance with the License. You
006 * may obtain a copy of the License at
007 *
008 * http://www.opensource.org/licenses/eclipse-1.0.php
009 *
010 * See the COPYRIGHT.txt file distributed with this work for information
011 * regarding copyright ownership.
012 */
013 package org.mmtk.plan.immix;
014
015 import static org.mmtk.policy.immix.ImmixConstants.MARK_LINE_AT_SCAN_TIME;
016
017 import org.mmtk.plan.TraceLocal;
018 import org.mmtk.plan.Trace;
019 import org.mmtk.policy.Space;
020 import org.mmtk.utility.HeaderByte;
021 import org.mmtk.utility.deque.ObjectReferenceDeque;
022 import org.mmtk.vm.VM;
023
024 import org.vmmagic.pragma.*;
025 import org.vmmagic.unboxed.*;
026
027 /**
028 * This class implements the thread-local functionality for a transitive
029 * closure over an immix space.
030 */
031 @Uninterruptible
032 public final class ImmixTraceLocal extends TraceLocal {
033
034 /****************************************************************************
035 *
036 * Instance fields
037 */
038 private final ObjectReferenceDeque modBuffer;
039
040 /**
041 * Constructor
042 *
043 * @param trace The trace associated with this trace local.
044 * @param modBuffer The modified objects buffer associated with this trace local. Possibly null.
045 */
046 public ImmixTraceLocal(Trace trace, ObjectReferenceDeque modBuffer) {
047 super(Immix.SCAN_IMMIX, trace);
048 this.modBuffer = modBuffer;
049 }
050
051 /****************************************************************************
052 *
053 * Externally visible Object processing and tracing
054 */
055
056 /**
057 * Is the specified object live?
058 *
059 * @param object The object.
060 * @return True if the object is live.
061 */
062 public boolean isLive(ObjectReference object) {
063 if (object.isNull()) return false;
064 if (Space.isInSpace(Immix.IMMIX, object)) {
065 return Immix.immixSpace.fastIsLive(object);
066 }
067 return super.isLive(object);
068 }
069
070 /**
071 * This method is the core method during the trace of the object graph.
072 * The role of this method is to:
073 *
074 * 1. Ensure the traced object is not collected.
075 * 2. If this is the first visit to the object enqueue it to be scanned.
076 * 3. Return the forwarded reference to the object.
077 *
078 * In this instance, we refer objects in the mark-sweep space to the
079 * immixSpace for tracing, and defer to the superclass for all others.
080 *
081 * @param object The object to be traced.
082 * @return The new reference to the same object instance.
083 */
084 @Inline
085 public ObjectReference traceObject(ObjectReference object) {
086 if (object.isNull()) return object;
087 if (Space.isInSpace(Immix.IMMIX, object))
088 return Immix.immixSpace.fastTraceObject(this, object);
089 return super.traceObject(object);
090 }
091
092 /**
093 * Ensure that the referenced object will not move from this point through
094 * to the end of the collection. This can involve forwarding the object
095 * if necessary.
096 *
097 * @param object The object that must not move during the collection.
098 * @return True If the object will not move during collection
099 */
100 @Inline
101 @Override
102 public boolean willNotMoveInCurrentCollection(ObjectReference object) {
103 if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(!Immix.immixSpace.inImmixDefragCollection());
104 return true;
105 }
106
107 /**
108 * Collectors that move objects <b>must</b> override this method.
109 * It performs the deferred scanning of objects which are forwarded
110 * during bootstrap of each copying collection. Because of the
111 * complexities of the collection bootstrap (such objects are
112 * generally themselves gc-critical), the forwarding and scanning of
113 * the objects must be dislocated. It is an error for a non-moving
114 * collector to call this method.
115 *
116 * @param object The forwarded object to be scanned
117 */
118 @Inline
119 @Override
120 protected void scanObject(ObjectReference object) {
121 super.scanObject(object);
122 if (MARK_LINE_AT_SCAN_TIME && Space.isInSpace(Immix.IMMIX, object))
123 Immix.immixSpace.markLines(object);
124 }
125
126 /**
127 * Process any remembered set entries. This means enumerating the
128 * mod buffer and for each entry, marking the object as unlogged
129 * (we don't enqueue for scanning since we're doing a full heap GC).
130 */
131 protected void processRememberedSets() {
132 if (modBuffer != null) {
133 logMessage(5, "clearing modBuffer");
134 while (!modBuffer.isEmpty()) {
135 ObjectReference src = modBuffer.pop();
136 HeaderByte.markAsUnlogged(src);
137 }
138 }
139 }
140 }