import json, yaml
from invirt.common import *
-from os import error, makedirs
-from os.path import dirname, getmtime
+from os.path import getmtime
default_src_path = '/etc/invirt/master.yaml'
-default_cache_path = '/var/lib/invirt/invirt.json'
+default_cache_path = '/var/lib/invirt/cache.json'
try: default_loader = yaml.CSafeLoader
except: default_loader = yaml.SafeLoader
if not do_refresh:
# try reading from the cache first
- try: cfg = wrap(file(cache_path), lambda f: json.read(f.read()))
+ try: cfg = with_closing(file(cache_path))(lambda f: json.read(f.read()))
except: do_refresh = True
if do_refresh:
- # reload the source and regenerate the cache
- cfg = wrap(file(src_path), lambda f: yaml.load(f, default_loader))
- try: wrap(file(cache_path, 'w'), lambda f: f.write(json.write(cfg)))
- except: pass # silent failure
+ # Atomically reload the source and regenerate the cache. The read and
+ # write must be a single transaction, or a stale version may be
+ # written.
+ @with_lock_file('/var/lib/invirt/cache.lock')
+ def cfg():
+ cfg = with_closing(file(src_path))(lambda f: yaml.load(f, default_loader))
+ try: with_closing(file(cache_path, 'w'))(lambda f: f.write(json.write(cfg)))
+ except: pass # silent failure
+ return cfg
return cfg
dicts = load()