ros_plugin_provider_cache.py

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import os
import shelve
import time

from .ros_plugin_provider import RosPluginProvider


class RosPluginProviderCache():

    """Cache persisting the plugin list to speed up start-up time."""

    def __init__(self):
        self._cache_file = os.path.expanduser('~/.config/ros.org/rqt-plugin-cache')
        self._loaded = None
        self._max_age = 60 * 60 * 24  # one day

    def load(self):
        if os.path.exists(self._cache_file):
            data = shelve.open(self._cache_file)
            ts = data['timestamp']
            if ts + self._max_age >= time.time():
                self._loaded = ts
                RosPluginProvider._cached_plugins = data['plugins']
                print('RosPluginProviderCache.load() using cached list of plugins')
            data.close()

    def save(self):
        data = shelve.open(self._cache_file)
        # only save data when not loaded before or not modified in between but has changes
        if self._loaded is None or (self._loaded == data['timestamp'] and RosPluginProvider._cached_plugins != data['plugins']):
            data['plugins'] = RosPluginProvider._cached_plugins
            data['timestamp'] = time.time()
            print('RosPluginProviderCache.save() written list of plugins to cache')
        data.close()