SimpleLinkedList for dart, success on single-thread but Failed when used with Future, requestAnimationFrame, httpRequest.onLoadEnd,...

AsyncSimpleLinkedList.dart

import 'dart:async';

class SimpleLinkedEntry {
  SimpleLinkedEntry _next = null;
  var _obj;
}

class AsyncSimpleLinkedList<E> {
  Future<SimpleLinkedEntry> _head = new Future.immediate(null);

  get length {
    return _head.then((h){
      int i = 0;
      for(var a = h; a != null; a = a._next, i++);
      return i;
    });
  }

  void add(E obj) {
    _head = _head.then((h){
      SimpleLinkedEntry e = new SimpleLinkedEntry();
      e._next = h;
      e._obj = obj;
      return e;
    });
  }

  num iterateAndRemove(bool f(E)) {
    _head = _head.then((h){
      var current = h;
      var prev = null;
      var head = null;
      int i = 0;
      bool c = false;
      while(current != null) {
        var cont = f(current._obj);
        if (!cont) {
          i++;
          if (prev != null) {
            prev._next = null;
          }
        } else {
          if (head == null) {
            head = current;
          }
          if (prev != null) {
            prev._next = current;
          }
          prev = current;
        }
        current = current._next;
      }
      return head;
    });
    return 0;
  }
}

LinkedBag.dart

class LinkedBag<E> {
  LinkedEntry _head = new LinkedEntry();

  get length {
    int i = 0;
    for(var a = _head; a != null; a = a._next) {
      if (a._obj != null) i++;
    }
    return i;
  }

  void add(E obj) {
    var a = _head;
    while(a != null) {
      if (a._obj == null) {
        a._obj = obj;
        return;
      }
      if (a._next == null) {
        var e = new LinkedEntry();
        e._obj = obj;
        a._next = e;
        return;
      }
      a = a._next;
    }
  }

  num iterateAndRemove(bool f(E)) {
    int i = 0;
    for(var current = _head; current != null; current = current._next) {
      if (current._obj != null) {
        var cont = f(current._obj);
        if (!cont) {
          i++;
          current._obj = null;
        }
      }
    }
    return i;
  }
}

class LinkedEntry {
  LinkedEntry _next = null;
  var _obj;
}

SimpleLinkedList.dart

class SimpleLinkedEntry {
  SimpleLinkedEntry _next = null;
  var _obj;
}

class SimpleLinkedList<E> {
  SimpleLinkedEntry _head = null;
  bool iterating = false;
  get length {
    int i = 0;
    for(var a = _head; a != null; a = a._next, i++);
    return i;
  }

  void add(E obj) {
    if (iterating) {
      print("try to add when iterating");
      throw new StateError("iterating");
    }
    SimpleLinkedEntry e = new SimpleLinkedEntry();
    e._next = _head;
    e._obj = obj;
    _head = e;
  }

  num iterateAndRemove(bool f(E)) {
    iterating = true;
    int i = 0;
    try {
      var current = _head;
      var prev = null;
      var head = null;
      bool c = false;
      while(current != null) {
        var cont = f(current._obj);
        if (!cont) {
          i++;
          if (prev != null) {
            prev._next = null;
          }
        } else {
          if (head == null) {
            head = current;
          }
          if (prev != null) {
            prev._next = current;
          }
          prev = current;
        }
        current = current._next;
      }
      _head = head;
    } finally {
      iterating = false;
    }
    return i;
  }
}

SimpleLinkedList.test.dart

import 'package:unittest/unittest.dart';

main() {
  test("SimpleLinkedList", () {
    var d = new SimpleLinkedList();
    d.add(1);
    d.add(2);
    d.add(3);
    d.add(1);
    expect(d.length, equals(4));

    var ndeleted = 0;
    var lbefore = 0;
    var lafter = 0;

    lbefore =  d.length;
    ndeleted = d.iterateAndRemove((v) => v != 2);
    lafter = d.length;
    expect(lafter, equals(lbefore - ndeleted), reason : "${lbefore} - ${ndeleted} != ${lafter}");

    lbefore =  d.length;
    ndeleted = d.iterateAndRemove((v) => v != 1);
    lafter = d.length;
    expect(lafter, equals(lbefore - ndeleted), reason : "${lbefore} - ${ndeleted} != ${lafter}");
    expect(d.length, equals(1));

    lbefore =  d.length;
    ndeleted = d.iterateAndRemove((v) => v != 1);
    lafter = d.length;
    expect(lafter, equals(lbefore - ndeleted), reason : "${lbefore} - ${ndeleted} != ${lafter}");
    expect(d.length, equals(1));

    d.add(3);
    d.add(1);
    d.add(1);
    expect(d.length, equals(4));

    lbefore =  d.length;
    ndeleted = d.iterateAndRemove((v) => v != 3);
    lafter = d.length;
    expect(lafter, equals(lbefore - ndeleted), reason : "${lbefore} - ${ndeleted} != ${lafter}");
    expect(d.length, equals(2));

    lbefore =  d.length;
    ndeleted = d.iterateAndRemove((v) => v != 1);
    lafter = d.length;
    expect(lafter, equals(lbefore - ndeleted), reason : "${lbefore} - ${ndeleted} != ${lafter}");
    expect(d.length, equals(0));
  });
}