Created
December 23, 2011 13:09
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Concurrent list sorter
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import static java.util.concurrent.TimeUnit.SECONDS; | |
import java.util.ArrayList; | |
import java.util.Arrays; | |
import java.util.Collections; | |
import java.util.List; | |
import java.util.concurrent.ArrayBlockingQueue; | |
import java.util.concurrent.Callable; | |
import java.util.concurrent.ExecutionException; | |
import java.util.concurrent.Future; | |
import java.util.concurrent.ThreadPoolExecutor; | |
public final class ConcurrentListSorter { | |
private final ThreadPoolExecutor executor; | |
private final List<Long> list; | |
public ConcurrentListSorter(final List<Long> list) { | |
this.list = list; | |
executor = new ThreadPoolExecutor(2, 2, 0, SECONDS, | |
new ArrayBlockingQueue<Runnable>(Integer.MAX_VALUE)); | |
} | |
public List<Long> sort() throws InterruptedException, ExecutionException { | |
Future<List<Long>> future1 = executor.submit(new Sorter(firstHalf(list))); | |
Future<List<Long>> future2 = executor.submit(new Sorter(secondHalf(list))); | |
return intercalate(future1.get(), future2.get()); | |
} | |
private List<Long> firstHalf(final List<Long> list) { | |
int half = list.size() / 2; | |
return new ArrayList<Long>(list.subList(0, half)); | |
} | |
private List<Long> secondHalf(final List<Long> list) { | |
int half = list.size() / 2; | |
return new ArrayList<Long>(list.subList(half, list.size())); | |
} | |
private List<Long> intercalate(final List<Long> firstHalf, | |
final List<Long> secondHalf) { | |
ArrayList<Long> intercalatedList = new ArrayList<Long>(); | |
while (hasAnyElementIn(firstHalf, secondHalf)) { | |
if (firstHalf.isEmpty()) { | |
intercalatedList.add(secondHalf.remove(0)); | |
} else if (secondHalf.isEmpty()) { | |
intercalatedList.add(firstHalf.remove(0)); | |
} else { | |
intercalatedList.add(removeLesserElement(firstHalf, secondHalf)); | |
} | |
} | |
return intercalatedList; | |
} | |
private boolean hasAnyElementIn(final List<Long> firstHalf, | |
final List<Long> secondHalf) { | |
return !(firstHalf.isEmpty() && secondHalf.isEmpty()); | |
} | |
private Long removeLesserElement(final List<Long> firstHalf, | |
final List<Long> secondHalf) { | |
if (firstHalf.get(0) < secondHalf.get(0)) { | |
return firstHalf.remove(0); | |
} else { | |
return secondHalf.remove(0); | |
} | |
} | |
private class Sorter implements Callable<List<Long>> { | |
private final List<Long> list; | |
private Sorter(final List<Long> list) { | |
this.list = list; | |
} | |
public List<Long> call() throws Exception { | |
Collections.sort(list); | |
return list; | |
} | |
} | |
} |
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