c# - Parallel.Foreach SQL querying sometimes results in Connection -

i need speed performing 12 queries in application. switched regular foreach parallel.foreach. error saying "executereader requires open , available connection connection's current state connecting." understanding since many of 12 queries using same initialcatalog, there not new connection of 12 , may problem? how can fix this? "sql" list of type "sql"- class string name, string connectiona , list of queries. here code:

 /// <summary>     /// connects sql, performs queries , stores results in list of datatables     /// </summary>     /// <returns>list of data tables each query in config file</returns>     public list<datatable> getalldata()     {         stopwatch sw = new stopwatch();         sw.start();         list<datatable> data = new list<datatable>();           list<sql> sql=new list<sql>();          sql 1 = new sql();          one.connection = "data source=xxx-sql1;initial catalog=xxxdb;integrated security=true";          one.name = "col1";          one.queries.add("select name [reports]");          one.queries.add("select other [reports2]");          sql.add(one);          sql 2 = new sql();          two.connection = "data source=xxx-sql1;initial catalog=xxxdb;integrated security=true";          two.name = "col2";          two.queries.add("select alternatename [reports1]");          sql.add(two);           sql 3 = new sql();          three.connection = "data source=yyy-sql2;initial catalog=yyydb;integrated security=true";          three.name = "col3";          three.queries.add("select frequency times");          sql.add(three);           try         {             // paralleloptions options = new paralleloptions();             //options.maxdegreeofparallelism = 3;             // parallel.foreach(sql, options, s =>             parallel.foreach(sql, s =>             //foreach (sql s in sql)             {                 foreach (string q in s.queries)                 {                     using (connection = new sqlconnection(s.connection))                     {                         connection.open();                         datatable dt = new datatable();                         dt.tablename = s.name;                         command = new sqlcommand(q, connection);                         sqldataadapter adapter = new sqldataadapter();                         adapter.selectcommand = command;                         adapter.fill(dt);                         //adapter.dispose();                          lock (data)                         {                             data.add(dt);                         }                     }                 }             }             );         }         catch (exception ex)         {             messagebox.show(ex.tostring(), "getalldata error");         }          sw.stop();         messagebox.show(sw.elapsed.tostring());          return data;     } 

here's sql class made you'd need:

/// <summary> /// class defines sql connection , respective queries /// </summary> public class sql {     /// <summary>     /// name of connection/query     /// </summary>     public string name { get; set; }     /// <summary>     /// sql connection string     /// </summary>     public string connection { get; set; }     /// <summary>     /// list of sql queries connection     /// </summary>     public list<string> queries = new list<string>(); } 

i refactor out business logic (connecting database).

public class sqloperation {     public sqloperation()     {         queries = new list<string>();     }      public string tablename { get; set; }     public string connectionstring { get; set; }     public list<string> queries { get; set; } }  public static list<datatable> getalldata(ienumerable<sqloperation> sql) {     var taskarray =         sql.selectmany(s =>             s.queries              .select(query =>                 task.run(() => //task.factory.startnew .net 4.0                     executequery(s.connectionstring, s.tablename, query))))             .toarray();      try     {         task.waitall(taskarray);     }     catch(aggregateexception e)     {         messagebox.show(e.tostring(), "getalldata error");     }      return taskarray.where(t => !t.isfaulted).select(t => t.result).tolist(); }  public static datatable executequery(string connectionstring, string tablename, string query) {     datatable datatable = null;      using (var connection = new sqlconnection(connectionstring))     {         datatable = new datatable();         datatable.tablename = tablename;         using(var command = new sqlcommand(query, connection))         {             connection.open();              using(var adapter = new sqldataadapter())             {                 adapter.selectcommand = command;                 adapter.fill(datatable);             }         }     }       return datatable; }