code: private CompletableFuture<Void> uniRunNow(Object r, Executor e, Runnable f) {
      Throwable x;
      CompletableFuture<Void> d = newIncompleteFuture();
      if (r instanceof AltResult && (x = ((AltResult) r).ex) != null)
        d.result = encodeThrowable(x, r);
      else
        try {
          if (e != null) {
            e.execute(new UniRun<T>(null, d, this, f));
          } else {
            f.run();
            d.result = NIL;
          }
        } catch (Throwable ex) {
          d.result = encodeThrowable(ex);
        }
      return d;
    }
docs: /* ------------- Two-input Completions --------------