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.jikesrvm.mm.mmtk;
014    
015    import org.jikesrvm.VM;
016    import org.jikesrvm.scheduler.Synchronization;
017    import org.jikesrvm.runtime.Entrypoints;
018    
019    import org.vmmagic.pragma.*;
020    import org.vmmagic.unboxed.Offset;
021    
022    /**
023     * A counter that supports atomic increment and reset.
024     */
025    @Uninterruptible
026    public final class SynchronizedCounter extends org.mmtk.vm.SynchronizedCounter {
027    
028      private static Offset offset = Offset.max();
029    
030      public static void boot() {
031        offset = Entrypoints.synchronizedCounterField.getOffset();
032      }
033    
034      @Entrypoint
035      private int count = 0;
036    
037      @Override
038      public int reset() {
039        //    int offset = Interface.synchronizedCounterOffset;
040        int oldValue = count;
041        int actualOldValue = Synchronization.fetchAndAdd(this, offset, -oldValue);
042        if (actualOldValue != oldValue) {
043          VM.sysWriteln("oldValue = ", oldValue);
044          VM.sysWriteln("actualOldValue = ", actualOldValue);
045          VM.sysFail("Concurrent use of SynchronizedCounter.reset");
046        }
047        return oldValue;
048      }
049    
050      @Override
051      public int increment() {
052        if (VM.VerifyAssertions) VM._assert(!offset.isMax());
053        return Synchronization.fetchAndAdd(this, offset, 1);
054      }
055    
056      @Override
057      public int peek() {
058        return count;
059      }
060    
061    }