/**
 * A step in a pipeline of an asynchronous computation. When the last step in the computation is
 * complete, some objects captured during the computation are closed.
 *
 * <p>A pipeline of {@code ClosingFuture}s is a tree of steps. Each step represents either an
 * asynchronously-computed intermediate value, or else an exception that indicates the failure or
 * cancellation of the operation so far. The only way to extract the value or exception from a step

        if( isOpen() ) {
            return;
        }
        fid = open0( flags, access, attrs, options );
        opened = true;
        tree_num = tree.tree_num;
    }
    boolean isOpen() {
        boolean ans = opened && isConnected() && tree_num == tree.tree_num;
        return ans;
    }
    void close( int f, long lastWriteTime ) throws SmbException {

        if( log.level >= 3 )