host-events: finalize Host event refactor

Finalize HOST_ADDED delivery after host setup, route topology replacements through HOST_CHANGED, and keep pools keyed by host_id. Add regression coverage for listener timing, immutable Host snapshots, and pool rebinding.

Author: dkropachev

cassandra/cluster.py

@@ -0,0 +1,150 @@
+# Copyright DataStax, Inc.
+#
+# 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.
+
+"""
+Internal driver event primitives.
+
+This module intentionally does not expose a public subscription API.  It is a
+small synchronous bus used to decouple driver subsystems that need to react to
+shared internal state changes.
+"""
+
+from collections import defaultdict
+import logging
+from threading import RLock
+
+
+log = logging.getLogger(__name__)
+
+
+HOST = "HOST"
+
+HOST_ADDED = "HOST_ADDED"
+HOST_REMOVED = "HOST_REMOVED"
+HOST_UP = "HOST_UP"
+HOST_DOWN = "HOST_DOWN"
+HOST_CHANGED = "HOST_CHANGED"
+
+
+class DriverEvent(object):
+    """
+    Internal event envelope.
+    """
+
+    __slots__ = ("type", "category", "payload", "source")
+
+    def __init__(self, event_type, category, payload=None, source=None):
+        self.type = event_type
+        self.category = category
+        self.payload = payload
+        self.source = source
+
+    def __repr__(self):
+        return "%s(type=%r, category=%r, payload=%r, source=%r)" % (
+            self.__class__.__name__, self.type, self.category, self.payload, self.source)
+
+
+class HostEventPayload(object):
+    """
+    Payload for host topology and runtime-state events.
+    """
+
+    __slots__ = (
+        "host_id", "host", "old_host", "new_host", "changed_fields",
+        "old_values", "new_values", "refresh_nodes")
+
+    def __init__(self, host=None, host_id=None, old_host=None, new_host=None,
+                 changed_fields=(), old_values=None, new_values=None,
+                 refresh_nodes=True):
+        if host is None:
+            host = new_host if new_host is not None else old_host
+
+        if host_id is None and host is not None:
+            host_id = host.host_id
+
+        self.host_id = host_id
+        self.host = host
+        self.old_host = old_host
+        self.new_host = new_host
+        self.changed_fields = tuple(changed_fields or ())
+        self.old_values = old_values or {}
+        self.new_values = new_values or {}
+        self.refresh_nodes = refresh_nodes
+
+    def __repr__(self):
+        return ("%s(host_id=%r, host=%r, old_host=%r, new_host=%r, "
+                "changed_fields=%r, old_values=%r, new_values=%r)") % (
+                    self.__class__.__name__, self.host_id, self.host,
+                    self.old_host, self.new_host, self.changed_fields,
+                    self.old_values, self.new_values)
+
+
+class _EventBus(object):
+    """
+    Synchronous internal event bus.
+    """
+
+    def __init__(self):
+        self._type_subscribers = defaultdict(list)
+        self._category_subscribers = defaultdict(list)
+        self._lock = RLock()
+
+    def subscribe(self, event_type, handler):
+        with self._lock:
+            handlers = self._type_subscribers[event_type]
+            if handler not in handlers:
+                handlers.append(handler)
+
+    def unsubscribe(self, event_type, handler):
+        with self._lock:
+            self._remove_handler(self._type_subscribers.get(event_type), handler)
+
+    def subscribe_category(self, category, handler):
+        with self._lock:
+            handlers = self._category_subscribers[category]
+            if handler not in handlers:
+                handlers.append(handler)
+
+    def unsubscribe_category(self, category, handler):
+        with self._lock:
+            self._remove_handler(self._category_subscribers.get(category), handler)
+
+    def publish(self, event):
+        handlers = self._handlers_for_event(event)
+        for handler in handlers:
+            try:
+                handler(event)
+            except Exception:
+                log.exception("Error dispatching driver event %s to %r", event.type, handler)
+        return event
+
+    @staticmethod
+    def _remove_handler(handlers, handler):
+        if not handlers:
+            return
+        try:
+            handlers.remove(handler)
+        except ValueError:
+            pass
+
+    def _handlers_for_event(self, event):
+        with self._lock:
+            raw_handlers = list(self._type_subscribers.get(event.type, ()))
+            raw_handlers.extend(self._category_subscribers.get(event.category, ()))
+
+        handlers = []
+        for handler in raw_handlers:
+            if handler not in handlers:
+                handlers.append(handler)
+        return handlers

cassandra/events.py

@@ -37,6 +37,7 @@
 from cassandra import SignatureDescriptor, ConsistencyLevel, InvalidRequest, Unauthorized
 import cassandra.cqltypes as types
 from cassandra.encoder import Encoder
+from cassandra.events import DriverEvent, HOST, HOST_CHANGED, HostEventPayload
 from cassandra.marshal import varint_unpack
 from cassandra.protocol import QueryMessage
 from cassandra.query import dict_factory, bind_params
@@ -121,14 +122,22 @@ class Metadata(object):
     dbaas = False
     """ A boolean indicating if connected to a DBaaS cluster """
 
-    def __init__(self):
+    def __init__(self, event_bus=None):
         self.keyspaces = {}
         self.dbaas = False
         self._hosts = {}
         self._host_id_by_endpoint = {}
+        self._runtime_states = {}
+        self._event_bus = event_bus
         self._hosts_lock = RLock()
         self._tablets = Tablets({})
 
+    def set_event_bus(self, event_bus):
+        self._event_bus = event_bus
+        with self._hosts_lock:
+            for runtime_state in self._runtime_states.values():
+                runtime_state.set_event_bus(event_bus)
+
     def export_schema_as_string(self):
         """
         Returns a string that can be executed as a query in order to recreate
@@ -340,21 +349,30 @@ def add_or_return_host(self, host):
             try:
                 return self._hosts[host.host_id], False
             except KeyError:
+                host = self._bind_runtime_state(host)
                 self._host_id_by_endpoint[host.endpoint] = host.host_id
                 self._hosts[host.host_id] = host
                 return host, True
 
     def remove_host(self, host):
         self._tablets.drop_tablets_by_host_id(host.host_id)
         with self._hosts_lock:
+            current_host = self._hosts.get(host.host_id)
             self._host_id_by_endpoint.pop(host.endpoint, False)
+            if current_host is not None:
+                self._host_id_by_endpoint.pop(current_host.endpoint, False)
+            self._runtime_states.pop(host.host_id, None)
             return bool(self._hosts.pop(host.host_id, False))
 
     def remove_host_by_host_id(self, host_id, endpoint=None):
         self._tablets.drop_tablets_by_host_id(host_id)
         with self._hosts_lock:
-            if endpoint and self._host_id_by_endpoint[endpoint] == host_id:
+            current_host = self._hosts.get(host_id)
+            if endpoint and self._host_id_by_endpoint.get(endpoint) == host_id:
                 self._host_id_by_endpoint.pop(endpoint, False)
+            if current_host is not None:
+                self._host_id_by_endpoint.pop(current_host.endpoint, False)
+            self._runtime_states.pop(host_id, None)
             return bool(self._hosts.pop(host_id, False))
 
     def update_host(self, host, old_endpoint):
@@ -363,6 +381,65 @@ def update_host(self, host, old_endpoint):
             self._host_id_by_endpoint.pop(old_endpoint, False)
             self._host_id_by_endpoint[host.endpoint] = host.host_id
 
+    def replace_host(self, host_id, source=None, **fields):
+        """
+        Replace a Host topology snapshot for host_id and publish HOST_CHANGED.
+        """
+        with self._hosts_lock:
+            old_host = self._hosts.get(host_id)
+            if old_host is None:
+                return None, ()
+
+            changed_fields = []
+            old_values = {}
+            new_values = {}
+
+            for field, new_value in fields.items():
+                old_value = getattr(old_host, field)
+                if old_value != new_value:
+                    changed_fields.append(field)
+                    old_values[field] = old_value
+                    new_values[field] = new_value
+
+            if not changed_fields:
+                return old_host, ()
+
+            copy_kwargs = dict((field, fields[field]) for field in changed_fields)
+            new_host = old_host.copy_with(**copy_kwargs)
+            new_host.runtime_state.set_event_bus(self._event_bus)
+            new_host.runtime_state.bind_host(new_host)
+
+            self._hosts[host_id] = new_host
+            if "endpoint" in changed_fields:
+                if self._host_id_by_endpoint.get(old_host.endpoint) == host_id:
+                    self._host_id_by_endpoint.pop(old_host.endpoint, False)
+                self._host_id_by_endpoint[new_host.endpoint] = host_id
+            else:
+                self._host_id_by_endpoint[new_host.endpoint] = host_id
+
+        payload = HostEventPayload(
+            host_id=host_id,
+            old_host=old_host,
+            new_host=new_host,
+            changed_fields=tuple(changed_fields),
+            old_values=old_values,
+            new_values=new_values)
+        if self._event_bus:
+            self._event_bus.publish(DriverEvent(HOST_CHANGED, HOST, payload, source or self))
+        return new_host, tuple(changed_fields)
+
+    def _bind_runtime_state(self, host):
+        runtime_state = self._runtime_states.get(host.host_id)
+        if runtime_state is None:
+            runtime_state = host.runtime_state
+            self._runtime_states[host.host_id] = runtime_state
+        elif host.runtime_state is not runtime_state:
+            host = host.copy_with(runtime_state=runtime_state)
+
+        runtime_state.set_event_bus(self._event_bus)
+        runtime_state.bind_host(host)
+        return host
+
     def get_host(self, endpoint_or_address, port=None):
         """
         Find a host in the metadata for a specific endpoint. If a string inet address and port are passed,