Deprecate utility for eventlet

Change-Id: I22f1b04e10ceb8cbca00d654573838c694dcdbcf

releasenotes/notes/deprecate-eventlet-df4a34a7d56acc47.yaml

@@ -0,0 +1,10 @@
+---
+deprecations:
+  - |
+    Eventlet usages are deprecated and the removal of Eventlet from
+    OpenStack `is planned <https://governance.openstack.org/tc//goals/proposed/remove-eventlet.html>`_,
+    for this reason the eventlet_utils module is now deprecated.
+    The support of Eventlet will be soon removed from taskflow.
+
+    Please start considering removing your internal Eventlet usages and
+    start migrating your stack.

requirements.txt

@@ -7,6 +7,9 @@ pbr>=2.0.0 # Apache-2.0
 
 # Packages needed for using this library.
 
+# For deprecation warning
+debtcollector>=1.2.0 # Apache-2.0
+
 # For async and/or periodic work
 futurist>=1.2.0 # Apache-2.0
 

taskflow/utils/eventlet_utils.py

@@ -14,6 +14,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import debtcollector.removals
 from oslo_utils import importutils
 
 _eventlet = importutils.try_import('eventlet')
@@ -21,6 +22,7 @@ _eventlet = importutils.try_import('eventlet')
 EVENTLET_AVAILABLE = bool(_eventlet)
 
 
+@debtcollector.removals.remove(message='Eventlet support is deprecated.')
 def check_for_eventlet(exc=None):
     """Check if eventlet is available and if not raise a runtime error.