Make GC of repositories fully async for whitelisted namespaces

This change adds a worker to conduct GC on repositories with garbage every 10s.

Fixes #144

workers/gcworker.py

@@ -0,0 +1,30 @@
+import logging
+
+from apscheduler.schedulers.blocking import BlockingScheduler
+
+from app import app
+from data.database import UseThenDisconnect
+from data.model.repository import find_repository_with_garbage, garbage_collect_repo
+
+logger = logging.getLogger(__name__)
+sched = BlockingScheduler()
+
+@sched.scheduled_job(trigger='interval', seconds=10)
+def garbage_collect_repositories():
+  """ Performs garbage collection on repositories. """
+
+  with UseThenDisconnect(app.config):
+    repository = find_repository_with_garbage(app.config.get('EXP_ASYNC_GARBAGE_COLLECTION', []))
+    if repository is None:
+      logger.debug('No repository with garbage found')
+      return False
+
+    logger.debug('Starting GC of repository #%s (%s)', repository.id, repository.name)
+    garbage_collect_repo(repository)
+    logger.debug('Finished GC of repository #%s (%s)', repository.id, repository.name)
+    return True
+
+
+if __name__ == "__main__":
+  logging.basicConfig(level=logging.DEBUG)
+  sched.start()