only call flush only when available
only call flush only when available

tkerola/chainer,hvy/chainer,okuta/chainer,okuta/chainer,wkentaro/chainer,pfnet/chainer,niboshi/chainer,hvy/chainer,anaruse/chainer,wkentaro/chainer,ktnyt/chainer,ktnyt/chainer,jnishi/chainer,wkentaro/chainer,ktnyt/chainer,rezoo/chainer,jnishi/chainer,chainer/chainer,jnishi/chainer,hvy/chainer,niboshi/chainer,jnishi/chainer,keisuke-umezawa/chainer,okuta/chainer,niboshi/chainer,niboshi/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,okuta/chainer,chainer/chainer,ronekko/chainer,ktnyt/chainer,wkentaro/chainer,chainer/chainer,chainer/chainer,keisuke-umezawa/chainer,hvy/chainer