Fix for 2nd Connection hangs in Mirroring Environment

src/System.Data.SqlClient/src/System/Data/SqlClient/SqlInternalConnectionTds.cs

@@ -1416,7 +1416,7 @@ TimeoutTimer timeout
             // Determine unit interval
             if (timeout.IsInfinite)
             {
-                timeoutUnitInterval = checked((long)ADP.FailoverTimeoutStep * ADP.TimerFromSeconds(ADP.DefaultConnectionTimeout));
+                timeoutUnitInterval = checked((long)(ADP.FailoverTimeoutStep * ADP.TimerFromSeconds(ADP.DefaultConnectionTimeout)));
             }
             else
             {

src/System.Data.SqlClient/tests/ManualTests/SQL/MirroringTest/ConnectionOnMirroringTest.cs

@@ -0,0 +1,97 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Threading;
+
+namespace System.Data.SqlClient.ManualTesting.Tests
+{
+    public static class ConnectionOnMirroringTest
+    {
+        private static ManualResetEvent workerCompletedEvent = new ManualResetEvent(false);
+
+        [CheckConnStrSetupFact]
+        public static void TestMultipleConnectionToMirroredServer()
+        {
+            string mirroringStateDesc;
+            string failoverPartnerName;
+            bool isMirroring = GetMirroringInfo(DataTestUtility.TcpConnStr, out mirroringStateDesc, out failoverPartnerName);
+            bool isSynchronized = "SYNCHRONIZED".Equals(mirroringStateDesc, StringComparison.InvariantCultureIgnoreCase);
+            if (isMirroring && isSynchronized && !string.IsNullOrEmpty(failoverPartnerName))
+            {
+                SqlConnectionStringBuilder builder = new SqlConnectionStringBuilder(DataTestUtility.TcpConnStr);
+                builder.ConnectTimeout = 0;
+
+                TestWorker worker = new TestWorker(builder.ConnectionString);
+                Thread childThread = new Thread(() => worker.TestMultipleConnection());
+                childThread.Start();
+
+                if (workerCompletedEvent.WaitOne(10000))
+                {
+                    childThread.Join();
+                }
+                else
+                {
+                    // currently Thread.Abort() throws PlatformNotSupportedException in CoreFx.
+                    childThread.Interrupt();
+                    throw new Exception("SqlConnection could not open and close successfully in timely manner. Possibly connection hangs.");
+                }
+            }
+        }
+
+        private static bool GetMirroringInfo(string connectionString, out string mirroringStateDesc, out string failoverPartnerName)
+        {
+            mirroringStateDesc = null;
+            failoverPartnerName = null;
+
+            SqlConnectionStringBuilder builder = new SqlConnectionStringBuilder(connectionString);
+            string dbname = builder.InitialCatalog;
+
+            builder.ConnectTimeout = 5;
+            connectionString = builder.ConnectionString;
+
+            DataTable dt = DataTestUtility.RunQuery(connectionString, $"select mirroring_state_desc from sys.database_mirroring where database_id = DB_ID('{dbname}')");
+            mirroringStateDesc = dt.Rows[0][0].ToString();
+
+            bool isMirroring = !string.IsNullOrEmpty(mirroringStateDesc);
+            if (isMirroring)
+            {
+                dt = DataTestUtility.RunQuery(connectionString, $"select mirroring_partner_name from sys.database_mirroring where database_id = DB_ID('{dbname}')");
+                failoverPartnerName = dt.Rows[0][0].ToString();
+            }
+
+            return isMirroring;
+        }
+
+        private class TestWorker
+        {
+            private string _connectionString;
+
+            public TestWorker(string connectionString)
+            {
+                _connectionString = connectionString;
+            }
+
+            public void TestMultipleConnection()
+            {
+                List<SqlConnection> list = new List<SqlConnection>();
+
+                for (int i = 0; i < 10; ++i)
+                {
+                    SqlConnection conn = new SqlConnection(_connectionString);
+                    list.Add(conn);
+                    conn.Open();
+                }
+
+                foreach (SqlConnection conn in list)
+                {
+                    conn.Dispose();
+                }
+
+                workerCompletedEvent.Set();
+            }
+        }
+    }
+}

src/System.Data.SqlClient/tests/ManualTests/System.Data.SqlClient.ManualTesting.Tests.csproj

@@ -56,6 +56,7 @@
     <Compile Include="SQL\LocalDBTest\LocalDBTest.cs" />
     <Compile Include="SQL\MARSSessionPoolingTest\MARSSessionPoolingTest.cs" />
     <Compile Include="SQL\MARSTest\MARSTest.cs" />
+    <Compile Include="SQL\MirroringTest\ConnectionOnMirroringTest.cs" />
     <Compile Include="SQL\ParallelTransactionsTest\ParallelTransactionsTest.cs" />
     <Compile Include="SQL\SqlSchemaInfoTest\SqlSchemaInfoTest.cs" />
     <Compile Include="SQL\SqlBulkCopyTest\AdjustPrecScaleForBulkCopy.cs" />