X-Git-Url: http://xvm.mit.edu/gitweb/invirt/packages/invirt-base.git/blobdiff_plain/ff3dc91d38ee542dbb79c94ac910b43c2985b58e..56cf287cf395f1cd8f135cabb8531ff37d52e122:/files/usr/share/python-support/sipb-xen-base/invirt/common.py

diff --git a/files/usr/share/python-support/sipb-xen-base/invirt/common.py b/files/usr/share/python-support/sipb-xen-base/invirt/common.py
index ca90714..d986196 100644
--- a/files/usr/share/python-support/sipb-xen-base/invirt/common.py
+++ b/files/usr/share/python-support/sipb-xen-base/invirt/common.py
@@ -1,6 +1,5 @@
 import unittest
-from fcntl import flock, LOCK_EX, LOCK_UN
-from os import remove
+from fcntl import flock, LOCK_EX, LOCK_SH, LOCK_UN
 
 class struct(object):
     'A simple namespace object.'
@@ -26,13 +25,21 @@ def dicts2struct(x):
 #
 
 def with_closing(rsrc):
-    "Utility to emulate Python 2.5's `with closing(rsrc)` context manager."
+    """
+    Utility to emulate Python 2.5's `with closing(rsrc)` context manager.
+
+    E.g.,
+    @with_closing(file('/tmp/foo'))
+    def contents(f):
+        return f.read()
+    # now 'contents' is the contents of /tmp/foo
+    """
     def wrapper(func):
         try: return func(rsrc)
         finally: rsrc.close()
     return wrapper
 
-def with_lock_file(path):
+def with_lock_file(path, exclusive = True):
     """
     Context manager for lock files.  Example:
 
@@ -40,16 +47,17 @@ def with_lock_file(path):
     def input():
         print 'locked'
         return raw_input()
-    # decorator is executed immediately
-    print input # prints the input text
+    # prints 'locked'
+    print input # prints what raw_input() returned
     """
     def wrapper(func):
         @with_closing(file(path, 'w'))
         def g(f):
-            flock(f, LOCK_EX)
+            if exclusive: locktype = LOCK_EX
+            else:         locktype = LOCK_SH
+            flock(f, locktype)
             try: return func()
             finally: flock(f, LOCK_UN)
-        remove(path)
         return g
     return wrapper