+++ /dev/null
-import json
-from invirt.common import *
-from os.path import getmtime
-
-default_src_path = '/etc/invirt/master.yaml'
-default_cache_path = '/var/lib/invirt/cache.json'
-lock_file = '/var/lib/invirt/cache.lock'
-
-def load(src_path = default_src_path,
- cache_path = default_cache_path,
- force_refresh = False):
- """
- Try loading the configuration from the faster-to-load JSON cache at
- cache_path. If it doesn't exist or is outdated, load the configuration
- instead from the original YAML file at src_path and regenerate the cache.
- I assume I have the permissions to write to the cache directory.
- """
-
- # Namespace container for state variables, so that they can be updated by
- # closures.
- ns = struct()
-
- if force_refresh:
- do_refresh = True
- else:
- src_mtime = getmtime(src_path)
- try: cache_mtime = getmtime(cache_path)
- except OSError: do_refresh = True
- else: do_refresh = src_mtime + 1 >= cache_mtime
-
- # We chose not to simply say
- #
- # do_refresh = src_mtime >= cache_time
- #
- # because between the getmtime(src_path) and the time the cache is
- # rewritten, the master configuration may have been updated, so future
- # checks here would find a cache with a newer mtime than the master
- # (and thus treat the cache as containing the latest version of the
- # master). The +1 means that for at least a full second following the
- # update to the master, this function will refresh the cache, giving us
- # 1 second to write the cache. Note that if it takes longer than 1
- # second to write the cache, then this situation could still arise.
- #
- # The getmtime calls should logically be part of the same transaction
- # as the rest of this function (cache read + conditional cache
- # refresh), but to wrap everything in an flock would cause the
- # following cache read to be less streamlined.
-
- if not do_refresh:
- # Try reading from the cache first. This must be transactionally
- # isolated from concurrent writes to prevent reading an incomplete
- # (changing) version of the data (but the transaction can share the
- # lock with other concurrent reads). This isolation is accomplished
- # using an atomic filesystem rename in the refreshing stage.
- try: ns.cfg = with_closing(file(cache_path)) (
- lambda f: json.read(f.read()))
- except: do_refresh = True
-
- if do_refresh:
- # Atomically reload the source and regenerate the cache. The read and
- # write must be a single transaction, or a stale version may be
- # written (if another read/write of a more recent configuration
- # is interleaved). The final atomic rename is to keep this
- # transactionally isolated from the above cache read. If we fail to
- # acquire the lock, just try to load the master configuration.
- import yaml
- try: loader = yaml.CSafeLoader
- except: loader = yaml.SafeLoader
- try:
- @with_lock_file(lock_file)
- def refresh_cache():
- ns.cfg = with_closing(file(src_path)) (
- lambda f: yaml.load(f, loader))
- try: with_closing(file(cache_path + '.tmp', 'w')) (
- lambda f: f.write(json.write(ns.cfg)))
- except: pass # silent failure
- else: os.rename(cache_path + '.tmp', cache_path)
- except IOError:
- ns.cfg = with_closing(file(src_path)) (
- lambda f: yaml.load(f, loader))
- return ns.cfg
-
-dicts = load()
-structs = dicts2struct(dicts)
-
-# vim:et:sw=4:ts=4