presto-main/src/main/java/io/prestosql/execution/buffer/ClientBuffer.java/ClientBuffer/processRead
class ClientBuffer:    private void processRead(PendingRead pendingRead)
    {
        checkState(!Thread.holdsLock(this), "Can not process pending read while holding a lock on this");

        if (pendingRead.getResultFuture().isDone()) {
            return;
        }

        BufferResult bufferResult = processRead(pendingRead.getSequenceId(), pendingRead.getMaxSize());
        pendingRead.getResultFuture().set(bufferResult);
    }