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/*******************************************************************************
* Copyright (c) 2012 Ericsson
*
* All rights reserved. This program and the accompanying materials are made
* available under the terms of the Eclipse Public License v1.0 which
* accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors: Matthew Khouzam - Initial API and implementation
*******************************************************************************/
package org.eclipse.linuxtools.tmf.core.ctfadaptor;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Random;
/**
* Ctf Iterator Manager, allows mapping of iterators (a limited resource) to
* contexts (many many resources).
*
* @author Matthew Khouzam
* @version 1.0
* @since 1.1
*/
public abstract class CtfIteratorManager {
/*
* A side note synchronized works on the whole object, Therefore add and
* remove will be thread safe.
*/
/*
* The map of traces to trace managers.
*/
private static HashMap<CtfTmfTrace, CtfTraceManager> map = new HashMap<CtfTmfTrace, CtfTraceManager>();
/**
* Registers a trace to the iterator manager, the trace can now get
* iterators.
*
* @param trace
* the trace to register.
*/
public static synchronized void addTrace(final CtfTmfTrace trace) {
map.put(trace, new CtfTraceManager(trace));
}
/**
* Removes a trace to the iterator manager.
*
* @param trace
* the trace to register.
*/
public static synchronized void removeTrace(final CtfTmfTrace trace) {
map.remove(trace);
}
/**
* Get an iterator for a given trace and context.
*
* @param trace
* the trace
* @param ctx
* the context
* @return the iterator
*/
public static synchronized CtfIterator getIterator(final CtfTmfTrace trace,
final CtfTmfLightweightContext ctx) {
return map.get(trace).getIterator(ctx);
}
}
/**
* A trace manager
*
* @author Matthew Khouzam
*/
class CtfTraceManager {
/*
* Cache size. Under 1023 on linux32 systems. Number of file handles
* created.
*/
private final static int MAX_SIZE = 100;
/*
* The map of the cache.
*/
private final HashMap<CtfTmfLightweightContext, CtfIterator> fMap;
/*
* An array pointing to the same cache. this allows fast "random" accesses.
*/
private final ArrayList<CtfTmfLightweightContext> fRandomAccess;
/*
* The parent trace
*/
private final CtfTmfTrace fTrace;
/*
* Random number generator
*/
private final Random fRnd;
public CtfTraceManager(CtfTmfTrace trace) {
fMap = new HashMap<CtfTmfLightweightContext, CtfIterator>();
fRandomAccess = new ArrayList<CtfTmfLightweightContext>();
fRnd = new Random(System.nanoTime());
fTrace = trace;
}
/**
* This needs explaining: the iterator table is effectively a cache.
* Originally the contexts had a 1 to 1 structure with the file handles of a
* trace. This failed since there is a limit to how many file handles we can
* have opened simultaneously. Then a round-robin scheme was implemented,
* this lead up to a two competing contexts syncing up and using the same
* file handler, causing horrible slowdowns. Now a random replacement
* algorithm is selected. This is the same as used by arm processors, and it
* works quite well when many cores so this looks promising for very
* multi-threaded systems.
*
* @param context
* the context to look up
* @return the iterator refering to the context
*/
public CtfIterator getIterator(final CtfTmfLightweightContext context) {
/*
* if the element is in the map, we don't need to do anything else.
*/
CtfIterator retVal = fMap.get(context);
if (retVal == null) {
/*
* Assign an iterator to a context, this means we will need to seek
* at the end.
*/
if (fRandomAccess.size() < MAX_SIZE) {
/*
* if we're not full yet, just add an element.
*/
retVal = new CtfIterator(fTrace);
addElement(context, retVal);
} else {
/*
* if we're full, randomly replace an element
*/
retVal = replaceRandomElement(context);
}
retVal.seek((Long) context.getLocation().getLocation());
}
return retVal;
}
/**
* Add a pair of context and element to the hashmap and the arraylist.
*
* @param context
* the context
* @param elem
* the iterator
*/
private void addElement(final CtfTmfLightweightContext context,
final CtfIterator elem) {
fMap.put(context, elem);
fRandomAccess.add(context);
}
/**
* Replace a random element
*
* @param context
* the context to swap in
* @return the iterator of the removed elements.
*/
private CtfIterator replaceRandomElement(
final CtfTmfLightweightContext context) {
/*
* This needs some explanation too: We need to select a random victim
* and remove it. The order of the elements is not important, so instead
* of just calling arraylist.remove(element) which has an O(n)
* complexity, we pick an random number. The element is swapped out of
* the array and removed and replaced in the hashmap.
*/
final int size = fRandomAccess.size();
final int pos = fRnd.nextInt(size);
final CtfTmfLightweightContext victim = fRandomAccess.get(pos);
fRandomAccess.set(pos, context);
final CtfIterator elem = fMap.remove(victim);
fMap.put(context, elem);
return elem;
}
}
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