From 2c05818e4e51df1dde27db1f25b0eb493bc8be6f Mon Sep 17 00:00:00 2001 From: Yang Zhang Date: Fri, 1 Aug 2008 02:34:31 -0400 Subject: [PATCH 1/1] (partially) fixed the mtime comparison logic + comments svn path=/trunk/packages/sipb-xen-base/; revision=807 --- .../python-support/sipb-xen-base/invirt/config.py | 28 ++++++++++++++++---- 1 file changed, 23 insertions(+), 5 deletions(-) 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 6d0ab36..cead926 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 @@ -16,17 +16,35 @@ def load(src_path = default_src_path, I assume I have the permissions to write to the cache directory. """ - # Namespace container for various state variables, so that they can be - # updated by closures. + # Namespace container for state variables, so that they can be updated by + # closures. ns = struct() 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 + try: cache_mtime = getmtime(cache_path) + except OSError: do_refresh = True + else: do_refresh = src_mtime + 1 >= cache_mtime + + # We chose not to simply say + # + # do_refresh = src_mtime >= cache_time + # + # because between the getmtime(src_path) and the time the cache is + # rewritten, the master configuration may have been updated, so future + # checks here would find a cache with a newer mtime than the master + # (and thus treat the cache as containing the latest version of the + # master). The +1 means that for at least a full second following the + # update to the master, this function will refresh the cache, giving us + # 1 second to write the cache. Note that if it takes longer than 1 + # second to write the cache, then this situation could still arise. + # + # The getmtime calls should logically be part of the same transaction + # as the rest of this function (cache read + conditional cache + # refresh), but to wrap everything in an flock would cause the + # following cache read to be less streamlined. if not do_refresh: # Try reading from the cache first. This must be transactionally -- 1.7.9.5