Thread safe improvements on OIDCDiscoveryConfigListener (#4159)

* usage of CopyOnWriteArrayList/AtomicRef

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

* using concurrent hash map and atomic integer for ids

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

---------

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

data-plane/receiver/src/main/java/dev/knative/eventing/kafka/broker/receiver/impl/auth/OIDCDiscoveryConfigListener.java

@@ -20,12 +20,12 @@
 import io.vertx.core.Vertx;
 import java.io.File;
 import java.io.IOException;
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Objects;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -36,24 +36,27 @@ public class OIDCDiscoveryConfigListener implements AutoCloseable {
     private final Vertx vertx;
     private final FileWatcher configFeaturesWatcher;
     private final int timeoutSeconds;
-    private List<Consumer<OIDCDiscoveryConfig>> callbacks;
-    private OIDCDiscoveryConfig oidcDiscoveryConfig;
+    private final ConcurrentHashMap<Integer, Consumer<OIDCDiscoveryConfig>> callbacks;
+    private final AtomicReference<OIDCDiscoveryConfig> oidcDiscoveryConfig;
+    private final AtomicInteger callbackIdGenerator;
 
     public OIDCDiscoveryConfigListener(String featuresConfigPath, Vertx vertx, int timeoutSeconds) throws IOException {
         this.featuresConfigPath = featuresConfigPath;
         this.vertx = vertx;
         this.timeoutSeconds = timeoutSeconds;
+        this.oidcDiscoveryConfig = new AtomicReference<>();
+        this.callbacks = new ConcurrentHashMap<>();
+        this.callbackIdGenerator = new AtomicInteger(0);
 
         this.buildFeaturesAndOIDCDiscoveryConfig();
 
         this.configFeaturesWatcher =
                 new FileWatcher(new File(featuresConfigPath + "/" + FeaturesConfig.KEY_AUTHENTICATION_OIDC), () -> {
-                    if (this.oidcDiscoveryConfig == null) {
+                    if (this.oidcDiscoveryConfig.get() == null) {
                         this.buildFeaturesAndOIDCDiscoveryConfig();
-                        if (this.oidcDiscoveryConfig != null && this.callbacks != null) {
-                            this.callbacks.stream()
-                                    .filter(Objects::nonNull)
-                                    .forEach(c -> c.accept(this.oidcDiscoveryConfig));
+                        OIDCDiscoveryConfig config = this.oidcDiscoveryConfig.get();
+                        if (config != null) {
+                            this.callbacks.values().forEach(callback -> callback.accept(config));
                         }
                     }
                 });
@@ -62,27 +65,25 @@ public OIDCDiscoveryConfigListener(String featuresConfigPath, Vertx vertx, int t
     }
 
     public OIDCDiscoveryConfig getOidcDiscoveryConfig() {
-        return oidcDiscoveryConfig;
+        return oidcDiscoveryConfig.get();
     }
 
     public int registerCallback(Consumer<OIDCDiscoveryConfig> callback) {
-        if (this.callbacks == null) {
-            this.callbacks = new ArrayList<>();
-        }
-
-        this.callbacks.add(callback);
-        return this.callbacks.size() - 1;
+        int id = callbackIdGenerator.incrementAndGet();
+        this.callbacks.put(id, callback);
+        return id;
     }
 
     public void deregisterCallback(int callbackId) {
-        this.callbacks.set(callbackId, null);
+        this.callbacks.remove(callbackId);
     }
 
     private void buildOIDCDiscoveryConfig() throws ExecutionException, InterruptedException, TimeoutException {
-        this.oidcDiscoveryConfig = OIDCDiscoveryConfig.build(this.vertx)
+        OIDCDiscoveryConfig config = OIDCDiscoveryConfig.build(this.vertx)
                 .toCompletionStage()
                 .toCompletableFuture()
                 .get(this.timeoutSeconds, TimeUnit.SECONDS);
+        this.oidcDiscoveryConfig.set(config);
     }
 
     private void buildFeaturesAndOIDCDiscoveryConfig() {