X-Git-Url: http://xvm.mit.edu/gitweb/invirt/packages/invirt-base.git/blobdiff_plain/a397d9a4ae7892377e47497933aa0ed18667fea2..a11a45e1b18add76f2a440412ef6379a9874b082:/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 37fafb4..c27ba6b 100644
--- a/files/usr/share/python-support/sipb-xen-base/invirt/config.py
+++ b/files/usr/share/python-support/sipb-xen-base/invirt/config.py
@@ -1,13 +1,48 @@
-from __future__ import with_statement
-import yaml
+import json
+from invirt.common import *
+from os.path import getmtime
 
-default_path = '/etc/invirt/master.yaml'
+default_src_path   = '/etc/invirt/master.yaml'
+default_cache_path = '/var/lib/invirt/cache.json'
 
-try:    default_loader = yaml.CSafeLoader
-except: default_loader = yaml.SafeLoader
+def load(src_path = default_src_path,
+         cache_path = default_cache_path,
+         force_refresh = False):
+    """
+    Try loading the configuration from the faster-to-load JSON cache at
+    cache_path.  If it doesn't exist or is outdated, load the configuration
+    instead from the original YAML file at src_path and regenerate the cache.
+    I assume I have the permissions to write to the cache directory.
+    """
+    if force_refresh:
+        do_refresh = True
+    else:
+        src_mtime = getmtime(src_path)
+        try:            cache_mtime = getmtime(cache_path)
+        except OSError: do_refresh  = True
+        else:           do_refresh  = src_mtime > cache_mtime
 
-def load( path = default_path ):
-    with file( path ) as f:
-        return yaml.load( f, default_loader )
+    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:
+        # 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
+            try:    default_loader = yaml.CSafeLoader
+            except: default_loader = yaml.SafeLoader
+            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