stefan-egli commented on code in PR #12:
URL:
https://github.com/apache/sling-org-apache-sling-discovery-base/pull/12#discussion_r2065892578
##########
src/main/java/org/apache/sling/discovery/base/commons/BaseDiscoveryService.java:
##########
@@ -93,6 +97,18 @@ public TopologyView getTopology() {
.listInstances(localClusterView);
topology.addInstances(attachedInstances);
+ // Check if topology changes should be delayed
+ if (topologyReadinessHandler != null &&
topologyReadinessHandler.shouldDelayTopologyChange()) {
+ if (topologyReadinessHandler.isShutdown()) {
+ // On shutdown, mark oldView as not current to trigger
TOPOLOGY_CHANGING
+ if (oldView != null) {
+ oldView.setNotCurrent();
+ }
+ }
+ logger.debug("getTopology: topology changes are delayed, returning
old view");
+ return oldView;
Review Comment:
yes, I think this should work. I was wondering if the wording
`shouldDelayTopologyChange` applies for the shutdown case too.. more of a
naming aspect.
btw: in both cases the `oldView.isCurrent()` should return `false` after
this section - for the startup case that should be implicitly already the case,
for the normal case. There might be a race condition, although not very likely,
where the `topologyReadinessHandler` is still `null` and thus this section is
skipped. In that case the local instance would send a `TOPOLOGY_INIT` still. So
perhaps it might actually make it more robust if for both startup and shutdown
cases the `setNotCurrent` is explicitly called...
##########
src/main/java/org/apache/sling/discovery/base/commons/TopologyReadinessHandler.java:
##########
@@ -0,0 +1,166 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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.
+ */
+package org.apache.sling.discovery.base.commons;
+
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.apache.felix.hc.api.condition.SystemReady;
+import org.osgi.service.component.annotations.Activate;
+import org.osgi.service.component.annotations.Component;
+import org.osgi.service.component.annotations.Deactivate;
+import org.osgi.service.component.annotations.Reference;
+import org.osgi.service.component.annotations.ReferenceCardinality;
+import org.osgi.service.component.annotations.ReferencePolicy;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.osgi.service.component.ComponentContext;
+
+/**
+ * Coordinates topology changes based on system readiness state.
+ * This component ensures that topology changes only occur when the system is
in a stable state,
+ * both during startup and shutdown sequences.
+ *
+ * The handler manages three main states:
+ * 1. STARTUP: Initial state when the system is starting up
+ * 2. READY: System is ready for normal operation and topology changes
+ * 3. SHUTDOWN: System is in the process of shutting down
+ *
+ * State Transitions:
+ * - System starts in STARTUP state
+ * - Transitions to READY state only when SystemReady service is bound
+ * - Transitions to SHUTDOWN state when:
+ * * SystemReady service is unbound
+ * * Component is deactivated
+ *
+ * Note: This component requires the Felix SystemReady service to function
properly.
+ * The system will remain in STARTUP state until SystemReady service is bound,
+ * and will transition to SHUTDOWN state when the service is unbound.
+ */
+@Component(service = TopologyReadinessHandler.class, immediate = true)
+public class TopologyReadinessHandler {
+
+ private final Logger logger = LoggerFactory.getLogger(this.getClass());
+
+ /**
+ * Represents the possible states of the system with explicit transitions.
+ */
+ private enum SystemState {
+ STARTUP {
+ @Override
+ protected SystemState[] getAllowedTransitions() {
+ return new SystemState[] { READY };
+ }
+ },
+ READY {
+ @Override
+ protected SystemState[] getAllowedTransitions() {
+ return new SystemState[] { SHUTDOWN };
+ }
+ },
+ SHUTDOWN {
+ @Override
+ protected SystemState[] getAllowedTransitions() {
+ return new SystemState[] { }; // No transitions allowed from
SHUTDOWN
+ }
+ };
+
+ protected abstract SystemState[] getAllowedTransitions();
+ }
+
+ private final StateMachine stateMachine = new StateMachine();
+
+ @Reference(cardinality = ReferenceCardinality.MANDATORY, policy =
ReferencePolicy.STATIC)
+ private volatile SystemReady systemReady;
Review Comment:
does it work like this? (
[docu](https://github.com/apache/felix-dev/blob/master/healthcheck/api/src/main/java/org/apache/felix/hc/api/condition/SystemReady.java)
mentions it needs the tag `systemready` )
##########
bnd.bnd:
##########
@@ -4,4 +4,12 @@
# whitelist the private reference usage
-fixupmessages:"Export
org.apache.sling.discovery.base.connectors.announcement, has 1, private
references [org.apache.sling.discovery.base.connectors.announcement.impl]"; \
restrict:=warning; \
- is:=warn
\ No newline at end of file
+ is:=warn
+
+Bundle-Version: 3.0.0
Review Comment:
One thing I was always wondering: does the version need to be increased?
Could the `TopologyReadinessHandler` not be an internal detail of
discovery.base, and the package/major version would not have to be changed?
(but there might be another reason that I'm missing)
##########
src/main/java/org/apache/sling/discovery/base/commons/BaseDiscoveryService.java:
##########
@@ -41,12 +42,15 @@ public abstract class BaseDiscoveryService implements
DiscoveryService {
/** the old view previously valid and sent to the TopologyEventListeners
**/
private DefaultTopologyView oldView;
+ @Reference
+ private TopologyReadinessHandler topologyReadinessHandler;
+
protected abstract ClusterViewService getClusterViewService();
protected abstract AnnouncementRegistry getAnnouncementRegistry();
protected abstract void handleIsolatedFromTopology();
-
+
Review Comment:
detail: I'd remove this (there are a couple other similar cases in other
files)
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