"An item with the same key has already been added." when Parallel code

[doylecnn]

Read and complete the full issue template

Do not randomly delete sections. They are here for a reason.

Do you want to request a feature or report a bug?

• Bug
• Feature
• Question

Did you test against the latest CI build?

• Yes
• No

If you answered No, please test with the latest development build first.

Version of ClosedXML

0.95.4 and latest CI build (0.95.999.2311)

What is the current behavior?

get exception: An item with the same key has already been added. Key: 1, An item with the same key has already been added. Key: 20

What is the expected behavior or new feature?

no exception

Is this a regression from the previous version?

No

Reproducibility

Code to reproduce problem:

public void Main()
{
    var x = new ClosedXML.Excel.XLWorkbook();
    var s = x.AddWorksheet();
    var r = s.Row(1);
	System.Threading.Tasks.Parallel.For(1, 1000000, i => {
		var c1 = r.Cell(20);
		c1.SetValue(i);
	});
	Console.ReadLine();
}

the stack trace from inner exception:

   at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
   at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)
   at ClosedXML.Excel.XLCellsCollection.IncrementUsage(Dictionary`2 dictionary, Int32 key) in C:\projects\closedxml\ClosedXML\Excel\Cells\XLCellsCollection.cs:line 54
   at ClosedXML.Excel.XLCellsCollection.Add(Int32 row, Int32 column, XLCell cell) in C:\projects\closedxml\ClosedXML\Excel\Cells\XLCellsCollection.cs:line 33
   at ClosedXML.Excel.XLRangeBase.Cell(XLAddress& cellAddressInRange) in C:\projects\closedxml\ClosedXML\Excel\Ranges\XLRangeBase.cs:line 920
   at ClosedXML.Excel.XLRangeBase.Cell(Int32 row, Int32 column) in C:\projects\closedxml\ClosedXML\Excel\Ranges\XLRangeBase.cs:line 848
   at ClosedXML.Excel.XLRow.Cell(Int32 columnNumber) in C:\projects\closedxml\ClosedXML\Excel\Rows\XLRow.cs:line 144

lead me to:

ClosedXML/ClosedXML/Excel/Cells/XLCellsCollection.cs

Line 54 in 78150ef

dictionary.Add(key, 1);

• I attached a sample spreadsheet. (You can drag files on to this issue)

[igitur]

ClosedXML isn't thread-safe.

[kenleese]

Suggestion: Add “ClosedXML is not thread-safe” to a “Limitations” section of the project readme.

@igitur @Pankraty thank you for your ongoing efforts on this awesome project

[igitur]

Suggestion: Add “ClosedXML is not thread-safe” to a “Limitations” section of the project readme.

Frequent answers section added to the README.