Fix | Fix Bulk Copy Async deadlock with custom IDataReader using SqlDataReader internally. (#779)

Author: cheenamalhotra

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlBulkCopy.cs

@@ -1159,6 +1159,11 @@ private Task ReadFromRowSourceAsync(CancellationToken cts)
             }
             else
             { // This will call Read for DataRows, DataTable and IDataReader (this includes all IDataReader except DbDataReader)
+              // Release lock to prevent possible deadlocks
+                SqlInternalConnectionTds internalConnection = _connection.GetOpenTdsConnection();
+                bool semaphoreLock = internalConnection._parserLock.CanBeReleasedFromAnyThread;
+                internalConnection._parserLock.Release();
+
                 _hasMoreRowToCopy = false;
                 try
                 {
@@ -1175,6 +1180,10 @@ private Task ReadFromRowSourceAsync(CancellationToken cts)
                         throw;
                     }
                 }
+                finally
+                {
+                    internalConnection._parserLock.Wait(canReleaseFromAnyThread: semaphoreLock);
+                }
                 return null;
             }
         }