Merge Sort Isolate Example

MergeSortIsolateExample.dart

#import('dart:isolate', prefix:'isolate');

List split(List numbers) {
  int size = numbers.length;
  int middleIndex = (size/2).floor().toInt();
  var list1 = numbers.getRange(0, middleIndex);
  var list2 = numbers.getRange(middleIndex, size-middleIndex);
  return [list1, list2];
}

List merge(List a, List b) {
  int i = 0;
  int j = 0;
  List result = [];
  // These checks should not exist
  if (a == null && b != null) { return b; }
  if (b == null && a != null) { return a; }
  if (a == null && b == null) { return []; }

  while((i<a.length)  && (j<b.length)) {
    if (a[i] <= b[j]) {
      result.add(a[i++]);
    } else {
      result.add(b[j++]);
    }
  }

  if (i<a.length) {
    result.addAll(a.getRange(i, a.length-i));
  } else {
    result.addAll(b.getRange(j, b.length-j));
  }

  return result;
}

mergeSortIsolate() {
  isolate.port.receive((msg, reply) {
    mergeSort(msg).then((m) {
      reply.send(m);
      isolate.port.close();
    });
  });
}

Future<List> mergeSort(List arr) {
  if (arr.length == 0 || arr.length == 1) {
    return new Future.immediate(arr);
  }

  var s = split(arr);
  var w = Futures.wait([
      isolate.spawnFunction(mergeSortIsolate).call(s[0]),
      isolate.spawnFunction(mergeSortIsolate).call(s[1])]);
  return w.transform((values) => merge(values[0], values[1]));
}

void main() {
  var arr=[1,5,2,7,3,9,4,6,8];
  print(arr);
  isolate.spawnFunction(mergeSortIsolate).call(arr).then(print);
}

Example of how to do a merge sort using dart:isolate