PLINQ .AsParallel().ForAll throwing error - Index was out of range

Question

first i compose the LINQ query this way which worked properly without any error. here is my code

(from bk in Brokers.AsParallel()
 from prd in Periods.AsParallel()
 from _dsDb in dsDb.Tables[0].AsEnumerable().AsParallel()
 join _dtMain in dtMain.AsEnumerable().AsParallel()

 on new
 {
     val1 = _dsDb.Field<int>("ParentID"),
     val2 = _dsDb.Field<int>("ID"),
     val3 = _dsDb.Field<string>("Section"),
     val4 = _dsDb.Field<string>("LineItem"),
     val5 = _dsDb.Field<string>("DisplayInCSM")
 }
 equals new
 {
     val1 = _dtMain.Field<int>("ParentID"),
     val2 = _dtMain.Field<int>("ID"),
     val3 = _dtMain.Field<string>("Section"),
     val4 = _dtMain.Field<string>("LineItem"),
     val5 = _dtMain.Field<string>("DisplayInCSM")
 }

 where _dsDb.Field<string>("RowType") == "LineItem"
 && _dsDb.Field<int>("ParentID") == ParentID
 && _dsDb.Field<int>("ID") == ID
 && _dsDb.Field<string>("Broker") == bk.BrokerCode &&

 _dtMain.Field<string>("Type") == "Consensus"
 && _dtMain.Field<int>("ParentID") == ParentID
 && _dtMain.Field<int>("ID") == ID
 && _dtMain.Field<string>("Section") == Section
 && _dtMain.Field<string>("LineItem") == LineItem
 && _dtMain.Field<string>("DisplayInCSM") == DisplayInCSM

 select new { _dsDb, _dtMain, bk, prd }).ToList()
    .ForEach(x =>
    {
        x._dtMain.SetField("B_" + x.bk.BrokerCode + "_" + x.prd, (x._dsDb.Field<decimal?>(x.prd ?? "").ToString()));
        x._dtMain.SetField("file_date", (x._dsDb.Field<string>("Revise Date")));
    });

The moment i i use .AsParallel().ForAll() then program throwing error
Index was out of range. Must be non-negative and less than the size of the collection.

This way i use .AsParallel().ForAll() please review my code and tell me what is my mistake in code for which i am getting error.
how to fix the problem

(from bk in Brokers.AsParallel()
 from prd in Periods.AsParallel()
 from _dsDb in dsDb.Tables[0].AsEnumerable().AsParallel()
 join _dtMain in dtMain.AsEnumerable().AsParallel()

 on new
 {
     val1 = _dsDb.Field<int>("ParentID"),
     val2 = _dsDb.Field<int>("ID"),
     val3 = _dsDb.Field<string>("Section"),
     val4 = _dsDb.Field<string>("LineItem"),
     val5 = _dsDb.Field<string>("DisplayInCSM")
 }
 equals new
 {
     val1 = _dtMain.Field<int>("ParentID"),
     val2 = _dtMain.Field<int>("ID"),
     val3 = _dtMain.Field<string>("Section"),
     val4 = _dtMain.Field<string>("LineItem"),
     val5 = _dtMain.Field<string>("DisplayInCSM")
 }

 where _dsDb.Field<string>("RowType") == "LineItem"
 && _dsDb.Field<int>("ParentID") == ParentID
 && _dsDb.Field<int>("ID") == ID
 && _dsDb.Field<string>("Broker") == bk.BrokerCode &&

 _dtMain.Field<string>("Type") == "Consensus"
 && _dtMain.Field<int>("ParentID") == ParentID
 && _dtMain.Field<int>("ID") == ID
 && _dtMain.Field<string>("Section") == Section
 && _dtMain.Field<string>("LineItem") == LineItem
 && _dtMain.Field<string>("DisplayInCSM") == DisplayInCSM

 select new { _dsDb, _dtMain, bk, prd }).AsParallel()
    .ForAll(x =>
    {
        x._dtMain.SetField("B_" + x.bk.BrokerCode + "_" + x.prd, (x._dsDb.Field<decimal?>(x.prd ?? "").ToString()));
        x._dtMain.SetField("file_date", (x._dsDb.Field<string>("Revise Date")));
    });

Getting error when i add AsParallel with ForAll

.AsParallel()
        .ForAll(x =>
        {
            x._dtMain.SetField("B_" + x.bk.BrokerCode + "_" + x.prd, (x._dsDb.Field<decimal?>(x.prd ?? "").ToString()));
            x._dtMain.SetField("file_date", (x._dsDb.Field<string>("Revise Date")));
        });

Please help me to fix the problem. thanks

Answer 1

It is mentioned in the documentation of DataTable Class:

This type is safe for multithreaded read operations. You must synchronize any write operations.

For Datatable, parallel writing will cause many problems, so I suggest not to do this.

The explanation in this link is more detailed and easier to understand.

Is Parallel.forEach(DataTable.AsEnumerable() thread safe

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