Fix SessionDataSet: row count, async dispose, and null measurement issues (#53, #54, #55)

修复 SessionDataSet 行数统计、异步释放及空值测点问题

- Fix CurrentBatchRowCount() always returning 0 by eagerly constructing
  the first TsBlock in RpcDataSet constructor when initial data is available
  修复 CurrentBatchRowCount() 始终返回 0 的问题，在构造函数中预先反序列化首个 TsBlock

- Add IAsyncDisposable to SessionDataSet and RpcDataSet, providing
  DisposeAsync() that properly awaits Close() to avoid sync-over-async deadlocks
  为 SessionDataSet 和 RpcDataSet 添加 IAsyncDisposable 接口，支持 await using 语法

- Fix GetRow() including null-valued columns in RowRecord by using
  IsNull() check before calling type-specific getters, instead of relying
  on value type null checks which always pass for int/bool/float/etc.
  修复 GetRow() 中值类型默认值绕过 null 检查导致空值列被错误包含的问题

Author: CritasWang

src/Apache.IoTDB/DataStructure/RpcDataSet.cs

@@ -26,7 +26,7 @@
 
 namespace Apache.IoTDB.DataStructure
 {
-    public class RpcDataSet : System.IDisposable
+    public class RpcDataSet : System.IDisposable, System.IAsyncDisposable
     {
         private const string TimestampColumnName = "Time";
         private const string DefaultTimeFormat = "yyyy-MM-dd HH:mm:ss.fff";
@@ -140,6 +140,11 @@ public RpcDataSet(string sql, List<string> columnNameList, List<string> columnTy
             _tsBlockSize = 0;
             _tsBlockIndex = -1;
 
+            if (HasCachedByteBuffer())
+            {
+                ConstructOneTsBlock();
+            }
+
             _zoneId = FindTimeZoneSafe(zoneId);
 
             if (columnIndex2TsBlockColumnIndexList.Count != _columnNameList.Count)
@@ -172,6 +177,22 @@ public void Dispose()
             GC.SuppressFinalize(this);
         }
 
+        public async ValueTask DisposeAsync()
+        {
+            if (!disposedValue)
+            {
+                try
+                {
+                    await Close().ConfigureAwait(false);
+                }
+                catch
+                {
+                }
+                disposedValue = true;
+            }
+            GC.SuppressFinalize(this);
+        }
+
         public async Task Close()
         {
             if (_isClosed) return;
@@ -634,11 +655,9 @@ public RowRecord GetRow()
             long timestamp = 0;
             foreach (string columnName in columns)
             {
-                object localfield;
                 string typeStr = _columnTypeList[i];
                 TSDataType dataType = Client.GetDataTypeByStr(typeStr);
 
-                // Identify the real time column by tsBlock index, not by data type
                 int tsBlockColumnIndex = GetTsBlockColumnIndexForColumnName(columnName);
                 if (tsBlockColumnIndex == -1)
                 {
@@ -647,6 +666,13 @@ public RowRecord GetRow()
                     continue;
                 }
 
+                if (IsNull(tsBlockColumnIndex, _tsBlockIndex))
+                {
+                    i += 1;
+                    continue;
+                }
+
+                object localfield;
                 switch (dataType)
                 {
                     case TSDataType.BOOLEAN:
@@ -682,12 +708,9 @@ public RowRecord GetRow()
                         string err_msg = "value format not supported";
                         throw new TException(err_msg, null);
                 }
-                if (localfield != null)
-                {
-                    fieldList.Add(localfield);
-                    measurementList.Add(columnName);
-                    dataTypeList.Add(dataType);
-                }
+                fieldList.Add(localfield);
+                measurementList.Add(columnName);
+                dataTypeList.Add(dataType);
                 i += 1;
             }
             return new RowRecord(timestamp, fieldList, measurementList, dataTypeList);

src/Apache.IoTDB/DataStructure/SessionDataSet.cs

@@ -25,7 +25,7 @@
 
 namespace Apache.IoTDB.DataStructure
 {
-    public class SessionDataSet : System.IDisposable
+    public class SessionDataSet : System.IDisposable, System.IAsyncDisposable
     {
         private readonly long _queryId;
         private readonly long _statementId;
@@ -184,5 +184,21 @@ public void Dispose()
             Dispose(disposing: true);
             GC.SuppressFinalize(this);
         }
+
+        public async ValueTask DisposeAsync()
+        {
+            if (!disposedValue)
+            {
+                try
+                {
+                    await this.Close().ConfigureAwait(false);
+                }
+                catch
+                {
+                }
+                disposedValue = true;
+            }
+            GC.SuppressFinalize(this);
+        }
     }
 }