pvary commented on code in PR #10484:
URL: https://github.com/apache/iceberg/pull/10484#discussion_r1700304518


##########
flink/v1.19/flink/src/main/java/org/apache/iceberg/flink/maintenance/operator/TagBasedLockFactory.java:
##########
@@ -0,0 +1,152 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.iceberg.flink.maintenance.operator;
+
+import java.io.IOException;
+import java.util.Map;
+import org.apache.flink.annotation.Internal;
+import org.apache.iceberg.ManageSnapshots;
+import org.apache.iceberg.SnapshotRef;
+import org.apache.iceberg.Table;
+import org.apache.iceberg.flink.TableLoader;
+import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
+import org.apache.iceberg.util.Tasks;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Iceberg table {@link ManageSnapshots#createTag(String, long)}/{@link
+ * ManageSnapshots#removeTag(String)} based lock implementation for {@link 
TriggerLockFactory}.
+ */
+@Internal
+public class TagBasedLockFactory implements TriggerLockFactory {
+  private static final Logger LOG = 
LoggerFactory.getLogger(TagBasedLockFactory.class);
+  private static final String RUNNING_TAG = "__flink_maintenance_running";
+  private static final String RECOVERING_TAG = 
"__flink_maintenance_recovering";
+  private static final int CHANGE_ATTEMPTS = 3;
+
+  private final TableLoader tableLoader;
+  private transient Table table;
+
+  public TagBasedLockFactory(TableLoader tableLoader) {
+    this.tableLoader = tableLoader;
+  }
+
+  @Override
+  public void open() {
+    tableLoader.open();
+    this.table = tableLoader.loadTable();
+  }
+
+  @Override
+  public TriggerLockFactory.Lock createLock() {
+    return new Lock(table, RUNNING_TAG);
+  }
+
+  @Override
+  public TriggerLockFactory.Lock createRecoveryLock() {
+    return new Lock(table, RECOVERING_TAG);
+  }
+
+  @Override
+  public void close() throws IOException {
+    tableLoader.close();
+  }
+
+  public static class Lock implements TriggerLockFactory.Lock {
+    private final Table table;
+    private final String lockKey;
+
+    public Lock(Table table, String lockKey) {
+      Preconditions.checkNotNull(table, "Table should not be null");
+      Preconditions.checkNotNull(lockKey, "Lock key should not be null");
+      this.table = table;
+      this.lockKey = lockKey;
+    }
+
+    /**
+     * The lock will be acquired by jobs with creating a new tag. A new empty 
commit is added for a
+     * table without snapshots.
+     *
+     * @return <code>true</code> if the lock is acquired by this operator
+     */
+    @Override
+    public boolean tryLock() {
+      if (isHeld()) {
+        LOG.info("Lock is already held");
+        return false;
+      }
+
+      if (table.currentSnapshot() == null) {
+        // Create an empty commit
+        table.newFastAppend().commit();
+        LOG.info("Empty table, new empty commit added for using tags");
+      }
+
+      try {
+        Tasks.foreach(1)
+            .retry(CHANGE_ATTEMPTS)

Review Comment:
   > > wondering if retry is safe here. Could the lock/unblock action initiated 
by multiple threads/operator subtasks?
   > 
   > This is a valid issue. We need to write a more complicated locking with 
lockIds, and checks like we have in `MetastoreLock` and `LockRequest`. The main 
idea is to have something like `__flink_maitenance_<RND>` for the lock.
   > 
   > * For checking the lock, we check if there is any tag starting with 
`__flink_maitenance_`
   > * For creating the lock, we create a tag with a `__flink_maitenance_<RND>`
   > * For retries for creation, we check if the lock with `RND` is created, 
and if not, try to create again
   > * For removal, we list the locks and remove the tag with 
`__flink_maitenance_<RND>`
   > * For retries for removal, we check if the lock with the `RND` is removed, 
and if not, try to remove again
   
   Fixed this.



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