From: Yang Zhang <y_z@mit.edu>
Date: Mon, 28 Jul 2008 16:25:19 +0000 (-0400)
Subject: - added timestamp-based JSON caching of configuration for faster loading
X-Git-Tag: sipb-xen-base/8.8~1
X-Git-Url: http://xvm.mit.edu/gitweb/invirt/packages/invirt-base.git/commitdiff_plain/95eb488e71743cadb53e3d1af9e0d7ce5414ce9e

- added timestamp-based JSON caching of configuration for faster loading
- exposed (more) options to command-line frontend
- improved error messages/handling/help
- removed all python 2.5-isms
- reformatted to fit project style conventions

svn path=/trunk/packages/sipb-xen-base/; revision=771
---

diff --git a/files/usr/sbin/invirt-getconf b/files/usr/sbin/invirt-getconf
index c468499..d503dea 100755
--- a/files/usr/sbin/invirt-getconf
+++ b/files/usr/sbin/invirt-getconf
@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.5
+#!/usr/bin/env python
 
 """
 invirt-getconf [-f FILE] KEY prints the configuration the option named KEY from
@@ -19,39 +19,49 @@ from invirt.config import load
 from sys import argv, exit, stderr
 from optparse import OptionParser
 
-class invirt_exception( Exception ): pass
+class invirt_exception(Exception): pass
 
-def main( argv ):
+def main(argv):
     try:
-        parser = OptionParser()
-        parser.add_option('-f', '--file', default = '/etc/invirt/master.yaml',
-                help = 'the configuration file to read from')
-        options, args = parser.parse_args()
+        parser = OptionParser(usage = '%prog [options] key',
+                description = __doc__.strip().split('\n\n')[0])
+        parser.add_option('-s', '--src',
+                default = '/etc/invirt/master.yaml',
+                help = 'the source YAML configuration file to read from')
+        parser.add_option('-c', '--cache',
+                default = '/var/lib/invirt/invirt.json',
+                help = 'path to the JSON cache')
+        parser.add_option('-r', '--refresh',
+                action = 'store_true',
+                help = 'force the cache to be regenerated')
+        opts, args = parser.parse_args()
 
         try: [key] = args
-        except: raise invirt_exception( __doc__ )
+        except: raise invirt_exception(__doc__.strip())
 
-        conf = load()
+        conf = load(opts.src, opts.cache, opts.refresh)
         components = key.split('.')
-        for i, component in enumerate( components ):
-            progress = lambda: '.'.join( components[:i] )
-            if type( conf ) not in [ dict, list ]:
+        for i, component in enumerate(components):
+            progress = '.'.join(components[:i])
+            if type(conf) not in [dict, list]:
                 raise invirt_exception(
-                        'prematurely arrived at an atomic datum in the tree:\n'
-                        '%s has no children' % progress() )
-            if type( conf ) == list:
-                try: component = int( component )
+                        '%s: node has no children (atomic datum)' % progress)
+            if type(conf) == list:
+                try: component = int(component)
                 except: raise invirt_exception(
-                        '%s is a list, requires an integral path component '
-                        'but got "%s"' % ( progress(), component ) )
-            try: conf = conf[ component ]
+                        '%s: node a list; integer path component required, '
+                        'but got "%s"' % (progress, component))
+            try: conf = conf[component]
             except KeyError: raise invirt_exception(
-                    '"%s" not in "%s"' % ( component, progress() ) )
+                    '%s: key "%s" not found' % (progress, component))
+            except IndexError: raise invirt_exception(
+                    '%s: index %s out of range' % (progress, component))
         print conf
-    except invirt_exception, ex:
+    except (invirt_exception, OSError), ex:
         print >> stderr, ex
         return 1
 
-if __name__ == '__main__': exit( main( argv ) )
+if __name__ == '__main__':
+    exit(main(argv))
 
 # vim:et:sw=4:ts=4
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 ea4bf4e..dab9f20 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
@@ -1,11 +1,41 @@
-import yaml
+import json, yaml
+from os import error, makedirs
+from os.path import dirname, getmtime
 
-default_path = '/etc/invirt/master.yaml'
+default_src_path   = '/etc/invirt/master.yaml'
+default_cache_path = '/var/lib/invirt/invirt.json'
 
 try:    default_loader = yaml.CSafeLoader
 except: default_loader = yaml.SafeLoader
 
-def load( path = default_path ):
-    return yaml.load( file(path), default_loader )
+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):
+    """
+    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
+
+    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()))
+    return cfg
 
 # vim:et:sw=4:ts=4