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.utility.deque;
014    
015    import org.mmtk.utility.Constants;
016    
017    import org.mmtk.vm.VM;
018    
019    import org.vmmagic.unboxed.*;
020    import org.vmmagic.pragma.*;
021    
022    /**
023     * This supports <i>unsynchronized</i> pushing and popping of object
024     * references.  In addition, this can sort the entries currently on
025     * the shared stack.
026     */
027    @Uninterruptible public class SortTODObjectReferenceStack extends LocalDeque
028      implements Constants {
029    
030      /****************************************************************************
031       *
032       * Public instance methods
033       */
034    
035      /**
036       * Constructor
037       *
038       * @param queue The shared stack to which this stack will append
039       * its buffers (when full or flushed) and from which it will acquire new
040       * buffers when it has exhausted its own.
041       */
042      public SortTODObjectReferenceStack(SortTODSharedDeque queue) {
043        super(queue);
044      }
045    
046      /**
047       * Sort the address on the shared stack.
048       */
049      public final void sort() {
050        flushLocal();
051        ((SortTODSharedDeque) queue).sort();
052      }
053    
054      /**
055       * Push an address onto the address stack.
056       *
057       * @param object the object to be pushed onto the object queue
058       */
059      @Inline
060      public final void push(ObjectReference object) {
061        Address addr = object.toAddress();
062        if (VM.VERIFY_ASSERTIONS) VM.assertions._assert(!addr.isZero());
063        checkHeadInsert(1);
064        uncheckedHeadInsert(addr);
065      }
066    
067      /**
068       * Pop an address from the address stack, return zero if the stack
069       * is empty.
070       *
071       * @return The next address in the address stack, or zero if the
072       * stack is empty
073       */
074      @Inline
075      public final ObjectReference pop() {
076        if (checkDequeue(1)) {
077          return uncheckedDequeue().toObjectReference();
078        } else {
079          return ObjectReference.nullReference();
080        }
081      }
082    
083      /**
084       * Check if the (local and shared) stacks are empty.
085       *
086       * @return True if there are no more entries on the local & shared stack,
087       *         false otherwise.
088       */
089      @Inline
090      public final boolean isEmpty() {
091        return !checkDequeue(1);
092      }
093    }