import unittest
+from fcntl import flock, LOCK_EX, LOCK_UN
+from os import remove
class struct(object):
'A simple namespace object.'
- def __init__(self, d = {}):
+ def __init__(self, d = {}, **kwargs):
'd is the dictionary to update my __dict__ with.'
self.__dict__.update(d)
+ self.__dict__.update(kwargs)
def dicts2struct(x):
"""
else:
return x
-def wrap(rsrc, func):
- "Utility to that emulates with Python 2.5's `with closing(rsrc)`."
- try: return func(rsrc)
- finally: rsrc.close()
+#
+# Hacks to work around lack of Python 2.5's `with` statement.
+#
+
+def with_closing(rsrc):
+ "Utility to emulate Python 2.5's `with closing(rsrc)` context manager."
+ def wrapper(func):
+ try: return func(rsrc)
+ finally: rsrc.close()
+ return wrapper
+
+def with_lock_file(path):
+ """
+ Context manager for lock files. Example:
+
+ @with_lock_file('/tmp/mylock')
+ def input():
+ print 'locked'
+ return raw_input()
+ # decorator is executed immediately
+ print input # prints the input text
+ """
+ def wrapper(func):
+ @with_closing(file(path, 'w'))
+ def g(f):
+ flock(f, LOCK_EX)
+ try: return func()
+ finally: flock(f, LOCK_UN)
+ remove(path)
+ return g
+ return wrapper
+
+#
+# Tests.
+#
class common_tests(unittest.TestCase):
def test_dicts2structs(self):
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()