-import json, yaml
-from os import error, makedirs
-from os.path import dirname, getmtime
+import json
+from invirt.common import *
+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
-def wrap(rsrc, func):
- "Utility to that emulates with Python 2.5's `with closing(rsrc)`."
- try: return func(rsrc)
- finally: rsrc.close()
-
def load(src_path = default_src_path,
cache_path = default_cache_path,
force_refresh = False):
except OSError: do_refresh = True
else: do_refresh = src_mtime > cache_mtime
+ if not do_refresh:
+ # try reading from the cache first
+ 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))
- wrap(file(cache_path, 'w'), lambda f: f.write(json.write(cfg)))
- else:
- cfg = wrap(file(cache_path), lambda f: json.read(f.read()))
+ # 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():
+ import yaml
+ 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()
+structs = dicts2struct(dicts)
+
# vim:et:sw=4:ts=4