[FLINK-38061][mysql] Make defensive copies of collections in SnapshotPendingSplitsState to prevent concurrent modification issues

Author: Hisoka-X

flink-cdc-connect/flink-cdc-source-connectors/flink-cdc-base/src/main/java/org/apache/flink/cdc/connectors/base/source/assigner/state/SnapshotPendingSplitsState.java

@@ -26,6 +26,9 @@
 import io.debezium.relational.TableId;
 import io.debezium.relational.history.TableChanges;
 
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -89,17 +92,19 @@ public SnapshotPendingSplitsState(
             boolean isRemainingTablesCheckpointed,
             Map<String, Long> splitFinishedCheckpointIds,
             ChunkSplitterState chunkSplitterState) {
-        this.alreadyProcessedTables = alreadyProcessedTables;
-        this.remainingSplits = remainingSplits;
-        this.assignedSplits = assignedSplits;
-        this.splitFinishedOffsets = splitFinishedOffsets;
+        // FLINK-38061: make defensive copy to avoid potential concurrent modification of the
+        // collections.
+        this.alreadyProcessedTables = new ArrayList<>(alreadyProcessedTables);
+        this.remainingSplits = new ArrayList<>(remainingSplits);
+        this.assignedSplits = new LinkedHashMap<>(assignedSplits);
+        this.splitFinishedOffsets = new HashMap<>(splitFinishedOffsets);
         this.assignerStatus = assignerStatus;
-        this.remainingTables = remainingTables;
+        this.remainingTables = new ArrayList<>(remainingTables);
         this.isTableIdCaseSensitive = isTableIdCaseSensitive;
         this.isRemainingTablesCheckpointed = isRemainingTablesCheckpointed;
-        this.tableSchemas = tableSchemas;
+        this.tableSchemas = new HashMap<>(tableSchemas);
         this.chunkSplitterState = chunkSplitterState;
-        this.splitFinishedCheckpointIds = splitFinishedCheckpointIds;
+        this.splitFinishedCheckpointIds = new HashMap<>(splitFinishedCheckpointIds);
     }
 
     public Map<String, Long> getSplitFinishedCheckpointIds() {