我们有一个C#应用程序,可以在Excel文档中的工作表上填充表格.
必须按照从数据库返回行的顺序填充表.
对象DataFileColData定义为List并包含结果集行.出于测试目的,我只使用List的[0].
下面的代码段#1不起作用.不保留行顺序,因为尽管数字本身按顺序列出,但最终结果的数据是按顺序显示的:
if (DataFileColData[0].Count() > 0)
{
ConcurrentDictionary<int, DataRow> theRows = new ConcurrentDictionary<int, DataRow>(9, DataFileColData[0].Count());
Parallel.For(0, DataFileColData[0].Count(), i =>
{
// go through each column
int c = 0;
try
{
foreach (var Col in DataFileColData)
{
var cell = Col[i];
if (cell != null)
{
if (cell.GetType().Name == "JArray") //If Jarray then table compression was used not column compression
{
if (theRows.TryAdd(i, Dt.NewRow()))
theRows[i].ItemArray = JsonConvert.DeserializeObject<object[]>(Col[i].ToString());
}
else
{
if (theRows.TryAdd(i, Dt.NewRow()))
theRows[i][c] = cell;
}
}
c++;
}
} //try
catch (Exception e)
{
throw new Exception("Exception thrown in \"PublicMethods.cs | RenderExcelFile\" while in foreach loop over DataFileColData: " + e.ToString());
}
} //for
); //parallel
//Add the rows to the datatable in their original order
//(might have gotten skewed from the parallel.for loop)
for (int x = 0; x < theRows.Count; x++)
Dt.Rows.Add(theRows[x]);
//Set the name so it appears nicely in the Excel Name Box dropdown instead of "table1", "table2", etc etc.
Dt.TableName = ExcelTableSpec.TableTitle + " " + r.TableID;
}
下面的代码段#2可以处理与保留的每一行相关的行顺序和数据:
if (DataFileColData[0].Count() > 0)
{
DataRow[] theRows = new DataRow[DataFileColData[0].Count()];
Parallel.For(0, DataFileColData[0].Count(), i =>
{
DataRow Rw = Dt.NewRow();
// go through each column
int c = 0;
try
{
foreach (var Col in DataFileColData)
{
var cell = Col[i];
if (cell != null)
{
if (cell.GetType().Name == "JArray") //If Jarray then table compression was used not column compression
{
lock (theRows)
{
theRows[i] = Dt.NewRow();
theRows[i].ItemArray = JsonConvert.DeserializeObject<object[]>(Col[i].ToString());
}
}
else
{
lock (theRows)
{
theRows[i] = Dt.NewRow();
theRows[i][c] = cell;
}
}
}
c++;
}
} //try
catch (Exception e)
{
throw new Exception("Exception thrown in \"PublicMethods.cs | RenderExcelFile\" while in foreach loop over DataFileColData: " + e.ToString());
}
} //for
); //parallel
//Add the rows to the datatable in their original order
//(might have gotten skewed from the parallel.for loop)
Dt = theRows.CopyToDataTable();
//Set the name so it appears nicely in the Excel Name Box dropdown instead of "table1", "table2", etc etc.
Dt.TableName = ExcelTableSpec.TableTitle + " " + r.TableID;
}
我不明白为什么.我不认为需要锁定机制,因为每个线程都有自己的“i”实例,而ConcurrentDictionary应该是线程安全的.
有人能够向我解释为什么代码不按照我认为应该的方式工作?
谢谢!
根据@Enigmativity的评论更新代码如下.
MSDN文档不太清楚(对我来说无论如何),但似乎更新了DataTable,即使MSDN文档没有指出它在执行NewRow()方法时也是如此.
下面的新工作代码:
if (DataFileColData[0].Count() > 0)
{
DataRow[] theRows = new DataRow[DataFileColData[0].Count()];
Parallel.For(0, DataFileColData[0].Count(), i =>
//for (int i = 0; i < DataFileColData[0].Count(); i++)
{
lock (Dt)
{
theRows[i] = Dt.NewRow();
}
// go through each column
int c = 0;
try
{
foreach (var Col in DataFileColData)
{
var cell = Col[i];
if (cell != null)
{
if (cell.GetType().Name == "JArray") //If Jarray then table compression was used not column compression
{
theRows[i].ItemArray = JsonConvert.DeserializeObject<object[]>(Col[i].ToString());
}
else
{
theRows[i][c] = cell;
}
}
c += 1;
} //foreach
} //try
catch (Exception e)
{
throw new Exception("Exception thrown in \"PublicMethods.cs | RenderExcelFile\" while in foreach loop over DataFileColData: " + e.ToString());
}
} //for
); //parallel
//Add the rows to the datatable in their original order
//(might have gotten skewed from the parallel.for loop)
Dt = theRows.CopyToDataTable();
//Set the name so it appears nicely in the Excel Name Box dropdown instead of "table1", "table2", etc etc.
Dt.TableName = ExcelTableSpec.TableTitle + " " + r.TableID;
//cleanup
if (theRows != null)
Array.Clear(theRows, 0, theRows.Length);
theRows = null;
} //if (DataFileColData[0].Count() > 0)
最佳答案 请参阅(
MSDN Data Tables)的文档.
关键点是:
Thread Safety
This type is safe for multithreaded read operations. You must
synchronize any write operations.
所以不是我引起你问题的ConcurrentDictionary.
我已经反编译了NewRow方法,并且调用了NewRow(int record).此代码清楚地显示了写操作.
internal DataRow NewRow(int record)
{
if (-1 == record)
record = this.NewRecord(-1);
this.rowBuilder._record = record;
DataRow row = this.NewRowFromBuilder(this.rowBuilder);
this.recordManager[record] = row;
if (this.dataSet != null)
this.DataSet.OnDataRowCreated(row);
return row;
}