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;
014    
015    import org.mmtk.vm.VM;
016    import org.vmmagic.pragma.*;
017    import org.vmmagic.unboxed.*;
018    
019    /**
020     * This abstract class is the fundamental mechanism for performing a
021     * transitive closure over an object graph.<p>
022     *
023     * Some mechanisms only operate on nodes or edges, but due to limitations
024     * of inheritance we have combined these two here.
025     *
026     * @see org.mmtk.plan.TraceLocal
027     */
028    @Uninterruptible
029    public abstract class TransitiveClosure {
030    
031      /** Database of specialized scan classes. */
032      private static final Class<?>[] specializedScans = new Class[VM.activePlan.constraints().numSpecializedScans()];
033    
034      /**
035       * A transitive closure has been created that is designed to work with a specialized scan method. We must
036       * register it here so the specializer can return the class when queried.
037       *
038       * @param id The method id to register.
039       * @param specializedScanClass The class to register.
040       */
041      @Interruptible
042      public static synchronized void registerSpecializedScan(int id, Class<?> specializedScanClass) {
043        specializedScans[id] = specializedScanClass;
044      }
045    
046      /**
047       * Get the specialized scan with the given id.
048       */
049      public static Class<?> getSpecializedScanClass(int id) {
050        if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(specializedScans[id] != null);
051        return specializedScans[id];
052      }
053    
054      /** The specialized scan identifier */
055      protected final int specializedScan;
056    
057      /**
058       * Constructor
059       */
060      protected TransitiveClosure() {
061        this(-1);
062      }
063    
064      /**
065       * Constructor
066       *
067       * @param specializedScan The specialized scan for this trace.
068       */
069      protected TransitiveClosure(int specializedScan) {
070        this.specializedScan = specializedScan;
071        if (specializedScan >= 0) {
072          if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(getClass() == getSpecializedScanClass(specializedScan));
073        }
074      }
075    
076      /**
077       * Trace an edge during GC.
078       *
079       * @param source The source of the reference.
080       * @param slot The location containing the object reference.
081       */
082      public void processEdge(ObjectReference source, Address slot) {
083        VM.assertions.fail("processEdge not implemented.");
084      }
085    
086      /**
087       * Trace a node during GC.
088       *
089       * @param object The object to be processed.
090       */
091      public void processNode(ObjectReference object) {
092        VM.assertions.fail("processNode not implemented.");
093      }
094    }