Test pylsl flush vs pull_chunks gets correct timestamps with postproc enabled

pylsl_flush_v_pull.py

import pylsl
import numpy as np
import time
import sys, os


T_TOTAL = 70
T_SWITCH = 11.1


def main():

    srate = None
    inlet = None
    proc_on = True
    streams = pylsl.resolve_streams(2.0)
    for stream in streams:
        if stream.nominal_srate() != 0.0:
            inlet = pylsl.StreamInlet(stream, processing_flags=pylsl.proc_ALL if proc_on else pylsl.proc_none)
            srate = stream.nominal_srate()
            break

    do_flush = False

    timestamps = np.array([])
    t_start = pylsl.local_clock()
    t_switch = t_start
    splits = [t_switch]
    inlet.pull_chunk()  # First chunk often empty
    while inlet is not None:
        if do_flush:
            n_skipped = inlet.flush()
            timestamps = np.append(timestamps, np.nan * np.ones(n_skipped))
        else:
            samples, ts = inlet.pull_chunk()
            if len(ts) > 0:
                timestamps = np.append(timestamps, ts)
        t_now = pylsl.local_clock()
        if (t_now - t_switch) > T_SWITCH:
            splits.append(t_now)
            do_flush = not do_flush
            t_switch = t_now
            print("Switching modes")

        time.sleep(0.05)

        if (t_now - t_start) > T_TOTAL:
            inlet = None

    print(srate, len(timestamps) / (t_now - t_start))
    import matplotlib.pyplot as plt
    expected_ts = np.arange(len(timestamps)) / srate + timestamps[0]
    plt.plot(expected_ts, 1000 * (timestamps - expected_ts))
    plt.xlabel('Expected Timestamps (s)')
    plt.ylabel('Deviation From Expected (ms)')
    plt.title('LSL `flush` ts dev. with postproc ' + ('on' if proc_on else 'off'))
    plt.show()
    print("Break here")


if __name__ == '__main__':
    try:
        main()
    except KeyboardInterrupt:
        print('Interrupted')
        try:
            sys.exit(0)
        except SystemExit:
            os._exit(0)