deprecate using memcache_pool backend into an eventlet env.

Change-Id: I947a548a20dafb3b5f10f10f8d3a05a2ebfe1c22

oslo_cache/_bmemcache_pool.py

@@ -14,6 +14,7 @@
 # under the License.
 
 """Thread-safe connection pool for python-binary-memcached."""
+import debtcollector
 try:
     import eventlet
 except ImportError:
@@ -25,6 +26,16 @@ from oslo_log import log
 LOG = log.getLogger(__name__)
 
 
+if eventlet and eventlet.patcher.is_monkey_patched('thread'):
+    debtcollector.deprecate(
+        "Eventlet support is deprecated "
+        "and will be soon no longer supported. "
+        "This backend was originally designed to be compatible with Eventlet "
+        "and with monkey patching, so using this backend in an environment "
+        "with eventlet is now deprecated. "
+        "Please migrate your code and stop monkey patching your environment.")
+
+
 class _BMemcacheClient(bmemcached.Client):
     """Thread global memcache client
 

oslo_cache/_memcache_pool.py

@@ -22,6 +22,7 @@ import queue
 import threading
 import time
 
+import debtcollector
 try:
     import eventlet
 except ImportError:
@@ -36,6 +37,16 @@ from oslo_cache import exception
 LOG = log.getLogger(__name__)
 
 
+if eventlet and eventlet.patcher.is_monkey_patched('thread'):
+    debtcollector.deprecate(
+        "Eventlet support is deprecated "
+        "and will be soon no longer supported. "
+        "This backend was originally designed to be compatible with Eventlet "
+        "and with monkey patching, so using this backend in an environment "
+        "with eventlet is now deprecated. "
+        "Please migrate your code and stop monkey patching your environment.")
+
+
 class _MemcacheClient(memcache.Client):
     """Thread global memcache client
 

releasenotes/notes/deprecate-memcache_pool-backend-98f1267e4e912004.yaml

@@ -0,0 +1,11 @@
+---
+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, using the ``memcache_pool`` backend of oslo.cache
+    in an environment using eventlet is now deprecated.
+    The support of Eventlet will be soon removed from oslo.cache.
+
+    Please start considering removing your internal Eventlet usages and
+    start migrating your stack.

requirements.txt

@@ -7,3 +7,4 @@ oslo.config>=8.1.0 # Apache-2.0
 oslo.i18n>=5.0.0 # Apache-2.0
 oslo.log>=4.2.1 # Apache-2.0
 oslo.utils>=4.2.0 # Apache-2.0
+debtcollector>=3.0.0 # Apache-2.0