presto-main/src/main/java/io/prestosql/operator/HttpPageBufferClient.java/HttpPageBufferClient/initiateRequest
class HttpPageBufferClient:    private synchronized void initiateRequest()
    {
        scheduled = false;
        if (closed || (future != null)) {
            return;
        }

        if (completed) {
            sendDelete();
        }
        else {
            sendGetResults();
        }

        lastUpdate = DateTime.now();
    }