!7

static int n = 1000000;

// iterate safely (& quickly) in the face of concurrent modifications
static <A, B> IterableIterator<A> iterateKeysQuickly(final NavigableMap<A, B> map) {
  ret iteratorFromFunction(new F0<A>() {
    Iterator<A> it = keys(map).iterator();
    A key;
    
    A get() {
      synchronized(map) {
        try {
          if (!it.hasNext()) null;
          ret key = it.next();
        } catch (ConcurrentModificationException e) {
          print("Re-iterating");
          it = map.tailMap(key, false).keySet().iterator();
          if (!it.hasNext()) null;
          ret key = it.next(); // Can't throw another exception
        }
      }
    }
  });
}

p {
  final NavigableMap<S, Bool> map = synchroNavigableMap(litcimap());
  final new L<S> ids;
  repeat n {
    map.put(addAndReturn(ids, randomID()), Bool.TRUE);
  }
  
  repeat 5 {
    int i = 0;
    long sum = 0;
    time "Iterating" {
      for (S key : keys(map)) {
        if (!key.startsWith("_")) {
          ++i;
          sum += key.hashCode();
        }
      }
    }
    assertEquals(i, n);

    i = 0;
    long sum2 = 0;
    time "Iterating quickly" {
      for (S key : iterateKeysQuickly(map)) {
        if (!key.startsWith("_")) {
          ++i;
          sum2 += key.hashCode();
        }
      }
    }
    assertEquals(i, n);
    assertEquals(sum, sum2);
  }
}

Began life as a copy of #1012166