Sync the latest parse timestamps in main instead of __init__ in rss.

We should load the latest timestamps from the db when the thread starts
instead of doing it in the constructor.

The constructor may be invoked when the entities engine hasn't been
initialized yet, and result in deadlocks.

platypush/plugins/rss/__init__.py

@@ -4,17 +4,17 @@ import queue
 import re
 import threading
 import time
-
-from dateutil.tz import tzutc
 from typing import Iterable, Optional, Collection, Set
 from xml.etree import ElementTree
 
 import dateutil.parser
+from dateutil.tz import tzutc
 import requests
 
 from platypush.context import get_bus, get_plugin
 from platypush.message.event.rss import NewFeedEntryEvent
 from platypush.plugins import RunnablePlugin, action
+from platypush.plugins.variable import VariablePlugin
 from platypush.schemas.rss import RssFeedEntrySchema
 
 
@@ -61,8 +61,14 @@ class RssPlugin(RunnablePlugin):
         self._latest_entries = []
 
         self.subscriptions = list(self._parse_subscriptions(subscriptions or []))
+        self._latest_timestamps = {}
 
-        self._latest_timestamps = self._get_latest_timestamps()
+    @classmethod
+    @property
+    def _variable(cls) -> VariablePlugin:
+        var = get_plugin(VariablePlugin)
+        assert var, 'Could not load the variable plugin'
+        return var
 
     @staticmethod
     def _get_feed_latest_timestamp_varname(url: str) -> str:
@@ -70,21 +76,20 @@ class RssPlugin(RunnablePlugin):
 
     @classmethod
     def _get_feed_latest_timestamp(cls, url: str) -> Optional[datetime.datetime]:
-        t = (
-            get_plugin('variable')
-            .get(cls._get_feed_latest_timestamp_varname(url))
-            .output.get(cls._get_feed_latest_timestamp_varname(url))
-        )
+        varname = cls._get_feed_latest_timestamp_varname(url)
+        var: dict = cls._variable.get(varname).output or {}  # type: ignore
+        t = var.get(varname)
 
         if t:
             return dateutil.parser.isoparse(t)
 
+        return None
+
     def _get_latest_timestamps(self) -> dict:
         return {url: self._get_feed_latest_timestamp(url) for url in self.subscriptions}
 
     def _update_latest_timestamps(self) -> None:
-        variable = get_plugin('variable')
-        variable.set(
+        self._variable.set(
             **{
                 self._get_feed_latest_timestamp_varname(url): latest_timestamp
                 for url, latest_timestamp in self._latest_timestamps.items()
@@ -95,7 +100,7 @@ class RssPlugin(RunnablePlugin):
     def _parse_content(entry) -> Optional[str]:
         content = getattr(entry, 'content', None)
         if not content:
-            return
+            return None
 
         if isinstance(content, list):
             return content[0]['value']
@@ -139,7 +144,7 @@ class RssPlugin(RunnablePlugin):
                     for entry in feed.entries
                     if getattr(entry, 'published_parsed', None)
                 ],
-                key=lambda e: e['published'],
+                key=lambda e: e['published'],  # type: ignore
             ),
             many=True,
         )
@@ -316,6 +321,7 @@ class RssPlugin(RunnablePlugin):
         return ElementTree.tostring(root, encoding='utf-8', method='xml').decode()
 
     def main(self):
+        self._latest_timestamps = self._get_latest_timestamps()
         self._feed_workers = [
             threading.Thread(target=self._feed_worker, args=(q,))
             for q in self._feed_worker_queues