Comments

ambry-account/src/main/java/com/github/ambry/account/AccountMetadataStore.java

@@ -14,25 +14,97 @@
 package com.github.ambry.account;
 
 import java.util.Collection;
-
+import java.util.Map;
+import java.util.concurrent.locks.ReentrantLock;
+import org.I0Itec.zkclient.DataUpdater;
+import org.apache.helix.AccessOption;
+import org.apache.helix.ZNRecord;
+import org.apache.helix.store.HelixPropertyStore;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
- * An AccountMetadataStore is a storage to keep and retrieve {@link Account} metadata.
+ * An AccountMetadataStore is a storage to keep and retrieve {@link Account} metadata. This is the base
  */
-interface AccountMetadataStore {
+abstract class AccountMetadataStore {
+  private static final Logger logger = LoggerFactory.getLogger(LegacyMetadataStore.class);
+
+  protected final AccountServiceMetrics accountServiceMetrics;
+  protected final LocalBackup backup;
+  protected final String znRecordPath;
+  private final HelixPropertyStore<ZNRecord> helixStore;
+  private final ReentrantLock lock = new ReentrantLock();
+
+  AccountMetadataStore(AccountServiceMetrics accountServiceMetrics, LocalBackup backup,
+      HelixPropertyStore<ZNRecord> helixStore, String znRecordPath) {
+    this.accountServiceMetrics = accountServiceMetrics;
+    this.backup = backup;
+    this.helixStore = helixStore;
+    this.znRecordPath = znRecordPath;
+  }
 
   /**
-   * fetchAndUpdateCache would fetch the latest full set of {@link Account} metadata and update the cache
-   * in the {@link HelixAccountService}.
-   * @param isCalledFromListener is true when this function is invoked from the listener callback function.
+   * ZKUpdater extends the {@link DataUpdater} with another method to  permform some clean up logic after
+   * an update.
    */
-  void fetchAndUpdateCache(boolean isCalledFromListener);
+  interface ZKUpdater extends DataUpdater<ZNRecord> {
+
+    /**
+     *  Called after {@link HelixPropertyStore} update the {@code znRecordPath} with the {@link ZKUpdater}.
+     * @param isUpdateSucceeded The result of the {@link HelixPropertyStore#update}.
+     */
+    void afterUpdate(boolean isUpdateSucceeded);
+  }
 
   /**
-   * updateAccounts updates the latest full set of {@link Account} metadata and save it in the storage.
+   * Fetch the {@link Account} metadata from the given ZNRecord. It should return null when there is no {@link Account}
+   * ever created before. Subclass can assume the {@link ZNRecord} passed in this function is not null;
+   * @param record The {@link ZNRecord} fetched from {@code znRecordPath}.
+   * @return {@link Account} metadata in a map.
+   */
+  abstract Map<String, String> fetchAccountMetadataFromZNRecord(ZNRecord record);
+
+  /**
+   * Create new {@link ZKUpdater} that will be used to update the accounts.
    * @param accounts The {@link Account} collection to update.
+   * @return the Specific {@link ZKUpdater} to update accounts with {@link HelixPropertyStore}.
+   */
+  abstract ZKUpdater createNewZKUpdater(Collection<Account> accounts);
+
+
+  /**
+   * fetchAccountMetadata would fetch the latest full set of {@link Account} metadata from the store. It returns null
+   * when there is no {@link Account} created.
+   * @return {@link Account} metadata in a map.
+   */
+  Map<String, String> fetchAccountMetadata() {
+    // when fetching account metadata, we need to fetch the list of blob ids that point to different versions of
+    // account metadata as well the latest version of account metadata.
+    lock.lock();
+    try {
+      long startTimeMs = System.currentTimeMillis();
+      logger.trace("Start reading account metadata blob ids list from path={}", znRecordPath);
+      ZNRecord znRecord = helixStore.get(znRecordPath, null, AccessOption.PERSISTENT);
+      logger.trace("Fetched ZNRecord from path={}, took time={} ms", znRecordPath, startTimeMs);
+      if (znRecord == null) {
+        logger.debug("The ZNRecord to read does not exist on path={}", znRecordPath);
+        return null;
+      }
+      return fetchAccountMetadataFromZNRecord(znRecord);
+    } finally {
+      lock.unlock();
+    }
+  }
+
+  /**
+   * updateAccounts updates the latest full set of {@link Account} metadata and save it in the storage.
+   * @param accounts The {@link Account} collection to update. It will not be null or empty.
    * @return false when there is any error.
    */
-  boolean updateAccounts(Collection<Account> accounts);
+  boolean updateAccounts(Collection<Account> accounts) {
+    ZKUpdater zkUpdater = createNewZKUpdater(accounts);
+    boolean hasSucceeded = helixStore.update(znRecordPath, zkUpdater, AccessOption.PERSISTENT);
+    zkUpdater.afterUpdate(hasSucceeded);
+    return hasSucceeded;
+  }
 }
-