hg: lambda/lambda/jdk: - ensure null values are retained

[Remi Forax]

On 12/04/2012 11:44 AM, Paul Sandoz wrote:
> Hi Remi,
>
> Many thanks, that is just the kind of VM-perspective advice i was looking for. I was assuming that the VM would be able to somehow inline the hot path to the else block.

yes, but you don't need a supplementary field for that.

>
> So you are suggesting something like this:
>
>                      T _t = (T) maskNull(t);
>                      if (lastSeen == null || !lastSeen.equals(_t)) {
>                          lastSeen = _t;
>                          downstream.accept(t);
>                      }

I was thinking to something like this:

             return new Sink.ChainedReference<T>(sink) {
                 private Object lastSeen;

                 @Override
                 public void begin(long size) {
                     lastSeen = null;            // not needed if end() is called in a finally ?
                     downstream.begin(-1);
                 }

                 @Override
                 public void end() {
                     lastSeen = null;
                     downstream.end();
                 }

                 @Override
                 public void accept(T t) {
                     if (t == null) {
                         if (lastSeen != NULL_OBJECT) {
                             lastSeen = NULL_OBJECT
                             downstream.accept(null);
                         }
                     } else if (lastSeen == null || !t.equals(lastSeen)) {
                         lastSeen = t;
                         downstream.accept((T)t);
                     }
                 }
             };


>
> rather than:
>
>                      if (t == null) {
>                          if (!seenNull) {
>                              seenNull = true;
>                              downstream.accept(lastSeen = null);
>                          }
>                      } else if (lastSeen == null || !t.equals(lastSeen)) {
>                          downstream.accept(lastSeen = t);
>                      }
>
> Paul.

Rémi