Added convenience APIs for lockutils

The lock_file_prefix for each project doesn't need to be configurable or
frequently changed. This patch provides a convenience API which returns
a partial object of the synchronized decorator to avoid passing the prefix
each time locks are used.

The set_defaults method is also provided to change the default value of
lock_path when needed.

Fixes bug #1065524

Change-Id: I7b67f0a482da4be6d53a70db5bbd22dc91bdc10c

openstack/common/lockutils.py

@@ -49,6 +49,10 @@ CONF = cfg.CONF
 CONF.register_opts(util_opts)
 
 
+def set_defaults(lock_path):
+    cfg.set_defaults(util_opts, lock_path=lock_path)
+
+
 class _InterProcessLock(object):
     """Lock implementation which allows multiple locks, working around
     issues like bugs.debian.org/cgi-bin/bugreport.cgi?bug=632857 and does
@@ -247,3 +251,28 @@ def synchronized(name, lock_file_prefix, external=False, lock_path=None):
             return retval
         return inner
     return wrap
+
+
+def synchronized_with_prefix(lock_file_prefix):
+    """Partial object generator for the synchronization decorator.
+
+    Redefine @synchronized in each project like so::
+
+        (in nova/utils.py)
+        from nova.openstack.common import lockutils
+
+        synchronized = lockutils.synchronized_with_prefix('nova-')
+
+
+        (in nova/foo.py)
+        from nova import utils
+
+        @utils.synchronized('mylock')
+        def bar(self, *args):
+           ...
+
+    The lock_file_prefix argument is used to provide lock files on disk with a
+    meaningful prefix. The prefix should end with a hyphen ('-') if specified.
+    """
+
+    return functools.partial(synchronized, lock_file_prefix=lock_file_prefix)

tests/unit/test_lockutils.py

@@ -195,3 +195,19 @@ class LockTestCase(utils.BaseTestCase):
         finally:
             if os.path.exists(lock_dir):
                 shutil.rmtree(lock_dir, ignore_errors=True)
+
+    def test_synchronized_with_prefix(self):
+        lock_name = 'mylock'
+        lock_pfix = 'mypfix-'
+
+        foo = lockutils.synchronized_with_prefix(lock_pfix)
+
+        @foo(lock_name, external=True)
+        def bar(dirpath, pfix, name):
+            filepath = os.path.join(dirpath, '%s%s' % (pfix, name))
+            return os.path.isfile(filepath)
+
+        lock_dir = tempfile.mkdtemp()
+        self.config(lock_path=lock_dir)
+
+        self.assertTrue(bar(lock_dir, lock_pfix, lock_name))