utils.py

import time
import syslog
import subprocess
import traceback
from os import path


def log_init():
    syslog.openlog('hydroctrl')


def log(priority, message):
    priority_str = {
        syslog.LOG_INFO: 'INFO',
        syslog.LOG_WARNING: 'WARN',
        syslog.LOG_ERR: 'ERROR'
    }
    prefix = priority_str.get(priority, 'ERROR') + ': '
    print(prefix + message)
    syslog.syslog(priority, message)


def log_info(message):
    log(syslog.LOG_INFO, message)


def log_warn(message):
    log(syslog.LOG_WARNING, message)


def log_err(message):
    log(syslog.LOG_ERR, message)


def log_exception_trace():
    fmt = traceback.format_exc()
    for l in fmt.splitlines():
        log(syslog.LOG_INFO, '  ' + l)


def wait_for_ntp():
    """
    Wait until NTP selects a peer.
    """

    log_info('Waiting for NTP, press Ctrl+C to skip')

    try:
        while True:
            output = subprocess.check_output(['ntpq', '-pn'])
            lines = output.splitlines()[2:]  # skip header lines
            sync_peers = sum(l[0] == ord('*') for l in lines)  # sync peer is labelled with a star
            if sync_peers > 0:
                break
            log_info('Waiting for NTP')
            time.sleep(5)
    except KeyboardInterrupt:
        log_info('NTP status check skipped')
        return

    log_info('NTP status OK')


def retry(job, error_msg, attempts=3, delay=5, rethrow=True):
    while True:
        try:
            return job()
        except Exception:
            attempts -= 1

            log_info('%s, %d attempts left' % (error_msg, attempts))
            log_exception_trace()

            if attempts == 0:
                break
            else:
                time.sleep(delay)

    if rethrow:
        raise Exception(error_msg)


def config_file_path(file_name):
    script_dir = path.dirname(path.abspath(__file__))
    return path.join(script_dir, file_name)


def in_range(value, range):
    return min(range) <= value <= max(range)


def delay(secs):
    """
    This is more precise than time.sleep at the expense of
    keeping CPU busy.
    """

    start = time.monotonic()
    while secs > 0:
        end = time.monotonic()
        secs -= end - start
        start = end


def drop_uncertainty(*iterables):
    out = list(map(lambda x: x.value if hasattr(x, 'value') else x, iterables))
    return out if len(out) > 1 else out[0]