presto-main/src/main/java/io/prestosql/operator/HttpPageBufferClient.java/HttpPageBufferClient/close
class HttpPageBufferClient:    @Override
    public void close()
    {
        boolean shouldSendDelete;
        Future<?> future;
        synchronized (this) {
            shouldSendDelete = !closed;

            closed = true;

            future = this.future;

            this.future = null;

            lastUpdate = DateTime.now();
        }

        if (future != null && !future.isDone()) {
            future.cancel(true);
        }

        // abort the output buffer on the remote node; response of delete is ignored
        if (shouldSendDelete) {
            sendDelete();
        }
    }