Remove usage of contentmanager for executors

The context manager in the executor fit only for the blocking executor.
Even the dispatcher needs to run code before and after the application
callback, eventlet and future executors have to run the pre/post code
into the main thread and can run the callback into an other thread,
and that force them to run __enter__ and __exit__ manually and deal
the exception path.

This change adds a helper object instead of the context manager.
It is designed to be explicit on what must be executed
before and after the callback and what can be done in a thread or not.

All the executor code is now in the impl_pooledexecutor.py
and use the futures "PoolExecutor" API.

This use futurist to provide a eventlet and aioeventlet futures friendly
object.

Change-Id: I8cd7640f36beeda47560e3c82671bad3530e38d1

1 files changed, 55 insertions, 0 deletions

diff --git a/oslo_messaging/_utils.py b/oslo_messaging/_utils.py
index 532c98b..ddec6d7 100644
--- a/oslo_messaging/_utils.py
+++ b/oslo_messaging/_utils.py
@@ -13,6 +13,10 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import logging
+
+LOG = logging.getLogger(__name__)
+
 
 def version_is_compatible(imp_version, version):
     """Determine whether versions are compatible.
@@ -39,3 +43,54 @@ def version_is_compatible(imp_version, version):
             int(rev) > int(imp_rev)):  # Revision
         return False
     return True
+
+
+class DispatcherExecutorContext(object):
+    """Dispatcher executor context helper
+
+    A dispatcher can have work to do before and after the dispatch of the
+    request in the main server thread while the dispatcher itself can be
+    done in its own thread.
+
+    The executor can use the helper like this:
+
+        callback = dispatcher(incoming)
+        callback.prepare()
+        thread = MyWhateverThread()
+        thread.on_done(callback.done)
+        thread.run(callback.run)
+
+    """
+    def __init__(self, incoming, dispatch, executor_callback=None,
+                 post=None):
+        self._result = None
+        self._incoming = incoming
+        self._dispatch = dispatch
+        self._post = post
+        self._executor_callback = executor_callback
+
+    def run(self):
+        """The incoming message dispath itself
+
+        Can be run in an other thread/greenlet/corotine if the executor is
+        able to do it.
+        """
+        try:
+            self._result = self._dispatch(self._incoming,
+                                          self._executor_callback)
+        except Exception:
+            msg = 'The dispatcher method must catches all exceptions'
+            LOG.exception(msg)
+            raise RuntimeError(msg)
+
+    def done(self):
+        """Callback after the incoming message have been dispathed
+
+        Should be runned in the main executor thread/greenlet/corotine
+        """
+        # FIXME(sileht): this is not currently true, this works only because
+        # the driver connection used for polling write on the wire only to
+        # ack/requeue message, but what if one day, the driver do something
+        # else
+        if self._post is not None:
+            self._post(self._incoming, self._result)