Add a generic coordination lock mechanism

For various synchronized scenarios, this decorator
allows flexible lock name with parameters and names
of underlying functions.
For instance:
    @synchronized('{f_name}-{resource.id}-{snap[name]}')
    def foo(self, resource, snap):

Change-Id: I4bf75be2902cd598a5a5a2c5887d4b4262f3e042
Related-Bug: #1824911

neutron/common/coordination.py

@@ -0,0 +1,96 @@
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+"""Coordination and locking utilities."""
+
+import inspect
+
+import decorator
+from oslo_concurrency import lockutils
+from oslo_log import log
+from oslo_utils import timeutils
+import six
+
+LOG = log.getLogger(__name__)
+
+
+def synchronized(lock_name):
+    """Synchronization decorator.
+
+    :param str lock_name: Lock name.
+
+    Decorating a method like so::
+
+        @synchronized('mylock')
+        def foo(self, *args):
+           ...
+
+    ensures that only one process will execute the foo method at a time.
+
+    Different methods can share the same lock::
+
+        @synchronized('mylock')
+        def foo(self, *args):
+           ...
+
+        @synchronized('mylock')
+        def bar(self, *args):
+           ...
+
+    This way only one of either foo or bar can be executing at a time.
+
+    Lock name can be formatted using Python format string syntax::
+
+        @synchronized('{f_name}-{resource.id}-{snap[name]}')
+        def foo(self, resource, snap):
+           ...
+
+    Available field names are: decorated function parameters and
+    `f_name` as a decorated function name.
+    """
+
+    @decorator.decorator
+    def _synchronized(f, *a, **k):
+        if six.PY2:
+            # pylint: disable=deprecated-method
+            call_args = inspect.getcallargs(f, *a, **k)
+        else:
+            sig = inspect.signature(f).bind(*a, **k)
+            sig.apply_defaults()
+            call_args = sig.arguments
+        call_args['f_name'] = f.__name__
+        lock_format_name = lock_name.format(**call_args)
+        t1 = timeutils.now()
+        t2 = None
+        try:
+            with lockutils.lock(lock_format_name):
+                t2 = timeutils.now()
+                LOG.debug('Lock "%(name)s" acquired by "%(function)s" :: '
+                          'waited %(wait_secs)0.3fs',
+                          {'name': lock_format_name,
+                           'function': f.__name__,
+                           'wait_secs': (t2 - t1)})
+                return f(*a, **k)
+        finally:
+            t3 = timeutils.now()
+            if t2 is None:
+                held_secs = "N/A"
+            else:
+                held_secs = "%0.3fs" % (t3 - t2)
+            LOG.debug('Lock "%(name)s" released by "%(function)s" :: held '
+                      '%(held_secs)s',
+                      {'name': lock_format_name,
+                       'function': f.__name__,
+                       'held_secs': held_secs})
+
+    return _synchronized

neutron/tests/unit/common/test_coordination.py

@@ -0,0 +1,33 @@
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import mock
+from oslo_concurrency import lockutils
+
+from neutron.common import coordination
+from neutron.tests import base
+
+
+@mock.patch.object(lockutils, 'lock')
+class CoordinationTestCase(base.BaseTestCase):
+    def test_synchronized(self, get_lock):
+        @coordination.synchronized('lock-{f_name}-{foo.val}-{bar[val]}')
+        def func(foo, bar):
+            pass
+
+        foo = mock.Mock()
+        foo.val = 7
+        bar = mock.MagicMock()
+        bar.__getitem__.return_value = 8
+        func(foo, bar)
+        get_lock.assert_called_with('lock-func-7-8')

releasenotes/notes/coordination-df3c0bf55a0c4863.yaml

@@ -0,0 +1,10 @@
+---
+other:
+  - |
+    Add a generic coordination lock mechanism for various
+    scenarios. This decorator allows flexible lock name
+    with parameters and names of underlying functions. And
+    in order to achive backward compatibility with python2.7
+    several functions was copied from the old version of
+    python inspect. Once python2.7 is retired, we can drop
+    such duplication.

requirements.txt

@@ -7,6 +7,7 @@ Paste>=2.0.2 # MIT
 PasteDeploy>=1.5.0 # MIT
 Routes>=2.3.1 # MIT
 debtcollector>=1.2.0 # Apache-2.0
+decorator>=3.4.0 # BSD
 eventlet!=0.18.3,!=0.20.1,>=0.18.2 # MIT
 pecan>=1.3.2 # BSD
 httplib2>=0.9.1 # MIT