[CELEBORN-2219][CIP-14] Support PushMergedData in CppClient

common/src/main/java/org/apache/celeborn/common/write/DataBatches.java

@@ -59,6 +59,8 @@ public ArrayList<DataBatch> requireBatches(int requestSize) {
       totalSize = 0;
       return batches;
     }
+    // TODO: ArrayList.remove(0) in a loop is O(n^2) due to element shifting.
+    // Investigate subList(0, count).clear() or use LinkedList/ArrayDeque.
     ArrayList<DataBatch> retBatches = new ArrayList<>();
     int currentSize = 0;
     while (currentSize < requestSize) {

cpp/celeborn/client/CMakeLists.txt

@@ -20,6 +20,8 @@ add_library(
         writer/PushStrategy.cpp
         writer/ReviveManager.cpp
         writer/PushDataCallback.cpp
+        writer/PushMergedDataCallback.cpp
+        writer/DataBatches.cpp
         ShuffleClient.cpp
         compress/Decompressor.cpp
         compress/Lz4Decompressor.cpp