Start new mbus servers before stopping old ones

3 files changed, 20 insertions, 1 deletions

diff --git a/container-disc/src/main/java/com/yahoo/container/jdisc/ConfiguredApplication.java b/container-disc/src/main/java/com/yahoo/container/jdisc/ConfiguredApplication.java
index 7ea91726673..625bd87c2db 100644
--- a/container-disc/src/main/java/com/yahoo/container/jdisc/ConfiguredApplication.java
+++ b/container-disc/src/main/java/com/yahoo/container/jdisc/ConfiguredApplication.java
@@ -366,6 +366,12 @@ public final class ConfiguredApplication implements Application {
         synchronized (monitor) {
             Set<ServerProvider> serversToClose = createIdentityHashSet(startedServers);
             serversToClose.removeAll(currentServers);
+            for (ServerProvider server : currentServers) {
+                if ( ! startedServers.contains(server) && server.isMultiplexed()) {
+                    server.start();
+                    startedServers.add(server);
+                }
+            }
             if (serversToClose.size() > 0) {
                 log.info(String.format("Closing %d server instances", serversToClose.size()));
                 for (ServerProvider server : serversToClose) {
@@ -374,7 +380,7 @@ public final class ConfiguredApplication implements Application {
                 }
             }
             for (ServerProvider server : currentServers) {
-                if (!startedServers.contains(server)) {
+                if ( ! startedServers.contains(server)) {
                     server.start();
                     startedServers.add(server);
                 }
diff --git a/container-messagebus/src/main/java/com/yahoo/messagebus/jdisc/MbusServer.java b/container-messagebus/src/main/java/com/yahoo/messagebus/jdisc/MbusServer.java
index 8f21cb227d8..3cf3b4bf8b0 100644
--- a/container-messagebus/src/main/java/com/yahoo/messagebus/jdisc/MbusServer.java
+++ b/container-messagebus/src/main/java/com/yahoo/messagebus/jdisc/MbusServer.java
@@ -60,6 +60,11 @@ public final class MbusServer extends AbstractResource implements ServerProvider
     }
 
     @Override
+    public boolean isMultiplexed() {
+        return true;
+    }
+
+    @Override
     protected void destroy() {
         log.log(Level.FINE, "Destroying message bus server.");
         runState.set(State.STOPPED);
diff --git a/jdisc_core/src/main/java/com/yahoo/jdisc/service/ServerProvider.java b/jdisc_core/src/main/java/com/yahoo/jdisc/service/ServerProvider.java
index ef72e643dae..ecdc30400f1 100644
--- a/jdisc_core/src/main/java/com/yahoo/jdisc/service/ServerProvider.java
+++ b/jdisc_core/src/main/java/com/yahoo/jdisc/service/ServerProvider.java
@@ -49,4 +49,12 @@ public interface ServerProvider extends SharedResource {
      * Application} shutdown code.</p>
      */
     void close();
+
+    /**
+     * Whether multiple instances of this can coexist, by means of a multiplexer on top of any exclusive resource.
+     * If this is true, new instances to replace old ones, during a graph generation switch, will be started before
+     * the obsolete ones are stopped; otherwise, the old will be stopped, and then the new ones started.
+     */
+    default boolean isMultiplexed() { return false; }
+
 }