Wrapper for mean visibility subtraction in time.
    Doesn't work when called from pipeline using multiprocessing pool.

def meantsubpool(d, data_read):
    """ Wrapper for mean visibility subtraction in time.
    Doesn't work when called from pipeline using multiprocessing pool.
    """

    logger.info('Subtracting mean visibility in time...')
    data_read = numpyview(data_read_mem, 'complex64', datashape(d))
    tsubpart = partial(rtlib.meantsub, data_read)

    blranges = [(d['nbl'] * t/d['nthread'], d['nbl']*(t+1)/d['nthread']) for t in range(d['nthread'])]
    with closing(mp.Pool(1, initializer=initreadonly, initargs=(data_read_mem,))) as tsubpool:
        tsubpool.map(tsubpart, blr)