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         CtfTraceManager mgr = map.remove(trace);
  55         if (mgr != null) {
  56             mgr.clear();
  57         }
  58     }
  59
  60     /**
  61      * Get an iterator for a given trace and context.
  62      *
  63      * @param trace
  64      *            the trace
  65      * @param ctx
  66      *            the context
  67      * @return the iterator
  68      * @since 2.0
  69      */
  70     public static synchronized CtfIterator getIterator(final CtfTmfTrace trace,
  71             final CtfTmfContext ctx) {
  72         return map.get(trace).getIterator(ctx);
  73     }
  74 }
  75
  76 /**
  77  * A trace manager
  78  *
  79  * @author Matthew Khouzam
  80  */
  81 class CtfTraceManager {
  82     /*
  83      * Cache size. Under 1023 on linux32 systems. Number of file handles
  84      * created.
  85      */
  86     private final static int MAX_SIZE = 100;
  87     /*
  88      * The map of the cache.
  89      */
  90     private final HashMap<CtfTmfContext, CtfIterator> fMap;
  91     /*
  92      * An array pointing to the same cache. this allows fast "random" accesses.
  93      */
  94     private final ArrayList<CtfTmfContext> fRandomAccess;
  95     /*
  96      * The parent trace
  97      */
  98     private final CtfTmfTrace fTrace;
  99     /*
 100      * Random number generator
 101      */
 102     private final Random fRnd;
 103
 104     public CtfTraceManager(CtfTmfTrace trace) {
 105         fMap = new HashMap<CtfTmfContext, CtfIterator>();
 106         fRandomAccess = new ArrayList<CtfTmfContext>();
 107         fRnd = new Random(System.nanoTime());
 108         fTrace = trace;
 109     }
 110
 111     /**
 112      * This needs explaining: the iterator table is effectively a cache.
 113      * Originally the contexts had a 1 to 1 structure with the file handles of a
 114      * trace. This failed since there is a limit to how many file handles we can
 115      * have opened simultaneously. Then a round-robin scheme was implemented,
 116      * this lead up to a two competing contexts syncing up and using the same
 117      * file handler, causing horrible slowdowns. Now a random replacement
 118      * algorithm is selected. This is the same as used by arm processors, and it
 119      * works quite well when many cores so this looks promising for very
 120      * multi-threaded systems.
 121      *
 122      * @param context
 123      *            the context to look up
 124      * @return the iterator refering to the context
 125      */
 126     public CtfIterator getIterator(final CtfTmfContext context) {
 127         /*
 128          * if the element is in the map, we don't need to do anything else.
 129          */
 130         CtfIterator retVal = fMap.get(context);
 131         if (retVal == null) {
 132             /*
 133              * Assign an iterator to a context, this means we will need to seek
 134              * at the end.
 135              */
 136             if (fRandomAccess.size() < MAX_SIZE) {
 137                 /*
 138                  * if we're not full yet, just add an element.
 139                  */
 140                 retVal = fTrace.createIterator();
 141                 addElement(context, retVal);
 142
 143             } else {
 144                 /*
 145                  * if we're full, randomly replace an element
 146                  */
 147                 retVal = replaceRandomElement(context);
 148             }
 149             if (context.getLocation() != null) {
 150                 final CtfLocationData location = (CtfLocationData) context.getLocation().getLocationInfo();
 151                 retVal.seek(location);
 152             }
 153         }
 154         return retVal;
 155     }
 156
 157     /**
 158      * Add a pair of context and element to the hashmap and the arraylist.
 159      *
 160      * @param context
 161      *            the context
 162      * @param elem
 163      *            the iterator
 164      */
 165     private void addElement(final CtfTmfContext context,
 166             final CtfIterator elem) {
 167         fMap.put(context, elem);
 168         fRandomAccess.add(context);
 169     }
 170
 171     /**
 172      * Replace a random element
 173      *
 174      * @param context
 175      *            the context to swap in
 176      * @return the iterator of the removed elements.
 177      */
 178     private CtfIterator replaceRandomElement(
 179             final CtfTmfContext context) {
 180         /*
 181          * This needs some explanation too: We need to select a random victim
 182          * and remove it. The order of the elements is not important, so instead
 183          * of just calling arraylist.remove(element) which has an O(n)
 184          * complexity, we pick an random number. The element is swapped out of
 185          * the array and removed and replaced in the hashmap.
 186          */
 187         final int size = fRandomAccess.size();
 188         final int pos = fRnd.nextInt(size);
 189         final CtfTmfContext victim = fRandomAccess.get(pos);
 190         fRandomAccess.set(pos, context);
 191         final CtfIterator elem = fMap.remove(victim);
 192         fMap.put(context, elem);
 193         return elem;
 194     }
 195
 196     void clear() {
 197         for (CtfIterator iterator : fMap.values()) {
 198             iterator.dispose();
 199         }
 200         fMap.clear();
 201         fRandomAccess.clear();
 202     }
 203 }