[improve] Introduce the sync() API to ensure consistency on reads dur…

…ing critical metadata operation paths (#18518)

(cherry picked from commit 492a9c3)

pulsar-broker-common/src/main/java/org/apache/pulsar/broker/resources/BaseResources.java

@@ -92,6 +92,13 @@ protected CompletableFuture<Optional<T>> getAsync(String path) {
         return cache.get(path);
     }
 
+    protected CompletableFuture<Optional<T>> refreshAndGetAsync(String path) {
+        return store.sync(path).thenCompose(___ -> {
+            cache.invalidate(path);
+            return cache.get(path);
+        });
+    }
+
     protected void set(String path, Function<T, T> modifyFunction) throws MetadataStoreException {
         try {
             setAsync(path, modifyFunction).get(operationTimeoutSec, TimeUnit.SECONDS);

pulsar-broker-common/src/main/java/org/apache/pulsar/broker/resources/NamespaceResources.java

@@ -237,8 +237,18 @@ public CompletableFuture<List<String>> listPartitionedTopicsAsync(NamespaceName
         }
 
         public CompletableFuture<Optional<PartitionedTopicMetadata>> getPartitionedTopicMetadataAsync(TopicName tn) {
-            return getAsync(joinPath(PARTITIONED_TOPIC_PATH, tn.getNamespace(), tn.getDomain().value(),
-                    tn.getEncodedLocalName()));
+            return getPartitionedTopicMetadataAsync(tn, false);
+        }
+
+        public CompletableFuture<Optional<PartitionedTopicMetadata>> getPartitionedTopicMetadataAsync(TopicName tn,
+                                                                                                      boolean refresh) {
+            if (refresh) {
+                return refreshAndGetAsync(joinPath(PARTITIONED_TOPIC_PATH, tn.getNamespace(), tn.getDomain().value(),
+                        tn.getEncodedLocalName()));
+            } else {
+                return getAsync(joinPath(PARTITIONED_TOPIC_PATH, tn.getNamespace(), tn.getDomain().value(),
+                        tn.getEncodedLocalName()));
+            }
         }
 
         public boolean partitionedTopicExists(TopicName tn) throws MetadataStoreException {

pulsar-metadata/src/main/java/org/apache/pulsar/metadata/api/MetadataStore.java

@@ -50,6 +50,17 @@ public interface MetadataStore extends AutoCloseable {
      */
     CompletableFuture<Optional<GetResult>> get(String path);
 
+
+    /**
+     * Ensure that the next value read from  the local client will be up-to-date with the latest version of the value
+     * as it can be seen by all the other clients.
+     * @param path
+     * @return a handle to the operation
+     */
+    default CompletableFuture<Void> sync(String path) {
+        return CompletableFuture.completedFuture(null);
+    }
+
     /**
      * Return all the nodes (lexicographically sorted) that are children to the specific path.
      *

pulsar-metadata/src/main/java/org/apache/pulsar/metadata/impl/ZKMetadataStore.java

@@ -153,6 +153,24 @@ protected void receivedSessionEvent(SessionEvent event) {
         }
     }
 
+    @Override
+    public CompletableFuture<Void> sync(String path) {
+        CompletableFuture<Void> result = new CompletableFuture<>();
+        zkc.sync(path, new AsyncCallback.VoidCallback() {
+            @Override
+            public void processResult(int rc, String s, Object o) {
+                Code code = Code.get(rc);
+                if (code == Code.OK) {
+                    result.complete(null);
+                } else {
+                    MetadataStoreException e = getException(code, path);
+                    result.completeExceptionally(e);
+                }
+            }
+        }, null);
+        return result;
+    }
+
     @Override
     protected void batchOperation(List<MetadataOp> ops) {
         try {