Ensure that updates of generation are atomic.

3 files changed, 19 insertions, 8 deletions

diff --git a/config/src/main/java/com/yahoo/config/subscription/impl/ConfigSetSubscription.java b/config/src/main/java/com/yahoo/config/subscription/impl/ConfigSetSubscription.java
index c09dc4d2dd7..204284e22d0 100644
--- a/config/src/main/java/com/yahoo/config/subscription/impl/ConfigSetSubscription.java
+++ b/config/src/main/java/com/yahoo/config/subscription/impl/ConfigSetSubscription.java
@@ -37,14 +37,13 @@ public class ConfigSetSubscription<T extends ConfigInstance> extends ConfigSubsc
         do {
             ConfigInstance myInstance = getNewInstance();
             ConfigState<T> configState = getConfigState();
-            Long nextGen = configState.getGeneration() + 1;
             // User forced reload
             if (checkReloaded()) {
-                updateInstance(nextGen, myInstance);
+                updateInstance(myInstance);
                 return true;
             }
             if (!myInstance.equals(configState.getConfig())) {
-                updateInstance(nextGen, myInstance);
+                updateInstance(myInstance);
                 return true;
             }
             sleep();
@@ -61,8 +60,8 @@ public class ConfigSetSubscription<T extends ConfigInstance> extends ConfigSubsc
     }
 
     @SuppressWarnings("unchecked")
-    private void updateInstance(Long generation, ConfigInstance myInstance) {
-        setConfigIfChanged(generation, (T)myInstance);
+    private void updateInstance(ConfigInstance myInstance) {
+        setConfigIfChangedIncGen((T)myInstance);
     }
 
     @Override
diff --git a/config/src/main/java/com/yahoo/config/subscription/impl/ConfigSubscription.java b/config/src/main/java/com/yahoo/config/subscription/impl/ConfigSubscription.java
index 4573f4bdbc2..1da0f640ec7 100644
--- a/config/src/main/java/com/yahoo/config/subscription/impl/ConfigSubscription.java
+++ b/config/src/main/java/com/yahoo/config/subscription/impl/ConfigSubscription.java
@@ -175,6 +175,19 @@ public abstract class ConfigSubscription<T extends ConfigInstance> {
         this.config.set(new ConfigState<>(true, generation, true, config));
     }
 
+    void setConfigIncGen(T config) {
+        ConfigState<T> prev = this.config.get();
+        while ( !this.config.compareAndSet(prev, new ConfigState<>(true, prev.getGeneration()+1, true, config))) {
+            prev = this.config.get();
+        }
+    }
+
+    void setConfigIfChangedIncGen(T config) {
+        ConfigState<T> prev = this.config.get();
+        while (!this.config.compareAndSet(prev, new ConfigState<>(true, prev.getGeneration() + 1, !config.equals(prev.getConfig()), config))) {
+            prev = this.config.get();
+        }
+    }
     void setConfigIfChanged(Long generation, T config) {
         this.config.set(new ConfigState<>(true, generation, !config.equals(this.config.get().getConfig()), config));
     }
diff --git a/config/src/main/java/com/yahoo/config/subscription/impl/FileConfigSubscription.java b/config/src/main/java/com/yahoo/config/subscription/impl/FileConfigSubscription.java
index e2e7bc1d2a0..43c5e9a87f8 100644
--- a/config/src/main/java/com/yahoo/config/subscription/impl/FileConfigSubscription.java
+++ b/config/src/main/java/com/yahoo/config/subscription/impl/FileConfigSubscription.java
@@ -37,19 +37,18 @@ public class FileConfigSubscription<T extends ConfigInstance> extends ConfigSubs
     @Override
     public boolean nextConfig(long timeout) {
         if (!file.exists() && !file.isFile()) throw new IllegalArgumentException("Not a file: "+file);
-        Long nextGen = getConfigState().getGeneration() + 1;
         if (checkReloaded()) {
             log.log(LogLevel.DEBUG, "User forced config reload at " + System.currentTimeMillis());
             // User forced reload
             T  newConfig = updateConfig();
-            setConfigIfChanged(nextGen, updateConfig());
+            setConfigIfChangedIncGen(updateConfig());
             ConfigState<T> configState = getConfigState();
             log.log(LogLevel.DEBUG, "Config updated at " + System.currentTimeMillis() + ", changed: " + configState.isConfigChanged());
             log.log(LogLevel.DEBUG, "Config: " + configState.getConfig().toString());
             return true;
         }
         if (file.lastModified()!=ts) {
-            setConfig(nextGen, updateConfig());
+            setConfigIncGen(updateConfig());
             return true;
         }
         try {