2 from invirt.common import *
3 from os.path import getmtime
5 default_src_path = '/etc/invirt/master.yaml'
6 default_cache_path = '/var/lib/invirt/cache.json'
7 lock_file = '/var/lib/invirt/cache.lock'
9 def load(src_path = default_src_path,
10 cache_path = default_cache_path,
11 force_refresh = False):
13 Try loading the configuration from the faster-to-load JSON cache at
14 cache_path. If it doesn't exist or is outdated, load the configuration
15 instead from the original YAML file at src_path and regenerate the cache.
16 I assume I have the permissions to write to the cache directory.
18 # Namespace container for various state variables, so that they can be
19 # updated by closures.
25 src_mtime = getmtime(src_path)
26 try: cache_mtime = getmtime(cache_path)
27 except OSError: ns.do_refresh = True
28 else: ns.do_refresh = src_mtime > cache_mtime
31 # Try reading from the cache first. This must be transactionally
32 # isolated from concurrent writes to prevent reading an incomplete
33 # (changing) version of the data (but the transaction can share the
34 # lock with other concurrent reads).
35 @with_lock_file(lock_file, False)
37 try: ns.cfg = with_closing(file(cache_path))(lambda f: json.read(f.read()))
38 except: ns.do_refresh = True
41 # Atomically reload the source and regenerate the cache. The read and
42 # write must be a single transaction, or a stale version may be
44 @with_lock_file(lock_file)
47 try: default_loader = yaml.CSafeLoader
48 except: default_loader = yaml.SafeLoader
49 ns.cfg = with_closing(file(src_path))(lambda f: yaml.load(f, default_loader))
50 try: with_closing(file(cache_path, 'w'))(lambda f: f.write(json.write(ns.cfg)))
51 except: pass # silent failure
55 structs = dicts2struct(dicts)