* added file locking around cache

[invirt/packages/invirt-base.git] / files / usr / share / python-support / sipb-xen-base / invirt / config.py

diff --git a/files/usr/share/python-support/sipb-xen-base/invirt/config.py b/files/usr/share/python-support/sipb-xen-base/invirt/config.py
index dab9f20..02409a4 100644 (file)
--- a/files/usr/share/python-support/sipb-xen-base/invirt/config.py
+++ b/files/usr/share/python-support/sipb-xen-base/invirt/config.py
@@ -1,18 +1,13 @@
 import json, yaml
-from os import error, makedirs
-from os.path import dirname, getmtime
+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):
@@ -30,12 +25,24 @@ def load(src_path = default_src_path,
         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():
+            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