org.eclipse.linuxtools.tmf.core/src/org/eclipse/linuxtools/tmf/core/ctfadaptor/CtfIteratorManager.java

   1 /*******************************************************************************
   2  * Copyright (c) 2012 Ericsson
   3  *
   4  * All rights reserved. This program and the accompanying materials are made
   5  * available under the terms of the Eclipse Public License v1.0 which
   6  * accompanies this distribution, and is available at
   7  * http://www.eclipse.org/legal/epl-v10.html
   8  *
   9  * Contributors: Matthew Khouzam - Initial API and implementation
  10  *******************************************************************************/
  11 package org.eclipse.linuxtools.tmf.core.ctfadaptor;
  12
  13 import java.util.ArrayList;
  14 import java.util.HashMap;
  15 import java.util.Random;
  16
  17 /**
  18  * Ctf Iterator Manager, allows mapping of iterators (a limited resource) to
  19  * contexts (many many resources).
  20  *
  21  * @author Matthew Khouzam
  22  * @version 1.0
  23  * @since 1.1
  24  */
  25 public abstract class CtfIteratorManager {
  26     /*
  27      * A side note synchronized works on the whole object, Therefore add and
  28      * remove will be thread safe.
  29      */
  30
  31     /*
  32      * The map of traces to trace managers.
  33      */
  34     private static HashMap<CtfTmfTrace, CtfTraceManager> map = new HashMap<CtfTmfTrace, CtfTraceManager>();
  35
  36     /**
  37      * Registers a trace to the iterator manager, the trace can now get
  38      * iterators.
  39      *
  40      * @param trace
  41      *            the trace to register.
  42      */
  43     public static synchronized void addTrace(final CtfTmfTrace trace) {
  44         map.put(trace, new CtfTraceManager(trace));
  45     }
  46
  47     /**
  48      * Removes a trace to the iterator manager.
  49      *
  50      * @param trace
  51      *            the trace to register.
  52      */
  53     public static synchronized void removeTrace(final CtfTmfTrace trace) {
  54         map.remove(trace);
  55     }
  56
  57     /**
  58      * Get an iterator for a given trace and context.
  59      *
  60      * @param trace
  61      *            the trace
  62      * @param ctx
  63      *            the context
  64      * @return the iterator
  65      */
  66     public static synchronized CtfIterator getIterator(final CtfTmfTrace trace,
  67             final CtfTmfLightweightContext ctx) {
  68         return map.get(trace).getIterator(ctx);
  69     }
  70 }
  71
  72 /**
  73  * A trace manager
  74  *
  75  * @author Matthew Khouzam
  76  */
  77 class CtfTraceManager {
  78     /*
  79      * Cache size. Under 1023 on linux32 systems. Number of file handles
  80      * created.
  81      */
  82     private final static int MAX_SIZE = 100;
  83     /*
  84      * The map of the cache.
  85      */
  86     private final HashMap<CtfTmfLightweightContext, CtfIterator> fMap;
  87     /*
  88      * An array pointing to the same cache. this allows fast "random" accesses.
  89      */
  90     private final ArrayList<CtfTmfLightweightContext> fRandomAccess;
  91     /*
  92      * The parent trace
  93      */
  94     private final CtfTmfTrace fTrace;
  95     /*
  96      * Random number generator
  97      */
  98     private final Random fRnd;
  99
 100     public CtfTraceManager(CtfTmfTrace trace) {
 101         fMap = new HashMap<CtfTmfLightweightContext, CtfIterator>();
 102         fRandomAccess = new ArrayList<CtfTmfLightweightContext>();
 103         fRnd = new Random(System.nanoTime());
 104         fTrace = trace;
 105     }
 106
 107     /**
 108      * This needs explaining: the iterator table is effectively a cache.
 109      * Originally the contexts had a 1 to 1 structure with the file handles of a
 110      * trace. This failed since there is a limit to how many file handles we can
 111      * have opened simultaneously. Then a round-robin scheme was implemented,
 112      * this lead up to a two competing contexts syncing up and using the same
 113      * file handler, causing horrible slowdowns. Now a random replacement
 114      * algorithm is selected. This is the same as used by arm processors, and it
 115      * works quite well when many cores so this looks promising for very
 116      * multi-threaded systems.
 117      *
 118      * @param context
 119      *            the context to look up
 120      * @return the iterator refering to the context
 121      */
 122     public CtfIterator getIterator(final CtfTmfLightweightContext context) {
 123         /*
 124          * if the element is in the map, we don't need to do anything else.
 125          */
 126         CtfIterator retVal = fMap.get(context);
 127         if (retVal == null) {
 128             /*
 129              * Assign an iterator to a context, this means we will need to seek
 130              * at the end.
 131              */
 132             if (fRandomAccess.size() < MAX_SIZE) {
 133                 /*
 134                  * if we're not full yet, just add an element.
 135                  */
 136                 retVal = new CtfIterator(fTrace);
 137                 addElement(context, retVal);
 138
 139             } else {
 140                 /*
 141                  * if we're full, randomly replace an element
 142                  */
 143                 retVal = replaceRandomElement(context);
 144             }
 145             final CtfLocationData location = (CtfLocationData) context.getLocation().getLocation();
 146             retVal.seek( location);
 147         }
 148         return retVal;
 149     }
 150
 151     /**
 152      * Add a pair of context and element to the hashmap and the arraylist.
 153      *
 154      * @param context
 155      *            the context
 156      * @param elem
 157      *            the iterator
 158      */
 159     private void addElement(final CtfTmfLightweightContext context,
 160             final CtfIterator elem) {
 161         fMap.put(context, elem);
 162         fRandomAccess.add(context);
 163     }
 164
 165     /**
 166      * Replace a random element
 167      *
 168      * @param context
 169      *            the context to swap in
 170      * @return the iterator of the removed elements.
 171      */
 172     private CtfIterator replaceRandomElement(
 173             final CtfTmfLightweightContext context) {
 174         /*
 175          * This needs some explanation too: We need to select a random victim
 176          * and remove it. The order of the elements is not important, so instead
 177          * of just calling arraylist.remove(element) which has an O(n)
 178          * complexity, we pick an random number. The element is swapped out of
 179          * the array and removed and replaced in the hashmap.
 180          */
 181         final int size = fRandomAccess.size();
 182         final int pos = fRnd.nextInt(size);
 183         final CtfTmfLightweightContext victim = fRandomAccess.get(pos);
 184         fRandomAccess.set(pos, context);
 185         final CtfIterator elem = fMap.remove(victim);
 186         fMap.put(context, elem);
 187         return elem;
 188     }
 189
 190 }