Managed IBM MQ .Net Client v9.1.4 freezes on get via SSL when running on .Net Core 3.1

Question

MQQueue.Get() operation freezes for 5 minutes when getting a message from QueueManager using SSL on .NetCore 3.1. The same code works fine when running on .Net Framework (v4.8) or without SSL on both runtimes.

Details:

• Client: MQ Managed Client from NuGet (IBMMQDotnetClient/v9.1.4)
• Server: docker from tag ibmcom/mq:9.1.4.0-r1 with basic SSL config using SSLCIPH(ANY_TLS12) SSLCAUTH(OPTIONAL)
• Reproduced on: .Net Core 3.1.2 on Windows and .Net Core 3.1.1 on Linux
• MQ Logs: MqGet-framework48.zip, MqGet-core31.zip

My Findings:

• The attached MqGet-core31 tells:
  1. The client sends the get message request at 09:15:52.199588
  2. It receives response with message body almost immediately at 09:15:52.311050
  3. Then it calls another MQRcvThread.ReceiveOneTSH() to finish the get operation. It calls MQTCPConnection.Receive() and it freeze for 5 minutes to 09:20:52.412669
• Possible reason:
  • MQTCPConnection keeps original socket and MQEncryptedSocket instance wrapping the same socket via SslStream
  • The method MQTCPConnection.Receive() polls on the socket and then it calls MQEncryptedSocket.Read()
  • It looks like that data from the socket are read by SslStream in MQEncryptedSocket before the poll() method is called and poll() waits for its 5 minutes timeout. Or any other race condition around?
  • If I put a breakpoint before problematic poll() call and delay it for a moment, then it often passess without any delay!

Test Code:

This code finishes in ~2 seconds on .Net Framework, but it needs 5 minutes and ~2 seconds when it is run on .Net Core. (Win or Linux)

// import server's CA
MQConnectionPool.ImportServerCertificateAuthorityIfNotPresent(CertMqTestCa);

Hashtable properties = new Hashtable {
    {MQC.HOST_NAME_PROPERTY, Mq1QmSslAnyTls12.Host},
    {MQC.PORT_PROPERTY, Mq1QmSslAnyTls12.Port},
    {MQC.CHANNEL_PROPERTY, Mq1QmSslAnyTls12.ChannelName},
    {MQC.USER_ID_PROPERTY, "admin"},
    {MQC.PASSWORD_PROPERTY, "changeit"},
    {MQC.CCSID_PROPERTY, 819},
    {MQC.SSL_CIPHER_SPEC_PROPERTY, "TLS_RSA_WITH_AES_256_CBC_SHA256"},
    {MQC.SSL_CERT_STORE_PROPERTY, "*USER"}
};
MQQueueManager queueManager;
using (new MQCcsidSetter(properties)) {
    queueManager = new MQQueueManager(null, properties);
}

string requestText = Guid.NewGuid().ToString();
string queueName = "SV.MqConnectionPoolTest";
// put message - works fine
using (MQQueue queue = queueManager.AccessQueue(queueName, MQC.MQOO_OUTPUT + MQC.MQOO_FAIL_IF_QUIESCING)) {
    byte[] requestBytes = Encoding.UTF8.GetBytes(requestText);
    MQMessage requestMessage = new MQMessage {Expiry = 3000, Priority = 4, CharacterSet = 1208, MessageType = MQC.MQMT_DATAGRAM};
    requestMessage.Write(requestBytes, 0, requestBytes.GetLength(0));
    queue.Put(requestMessage, new MQPutMessageOptions());
}

// get message back from the same queue
using (MQQueue queue = queueManager.AccessQueue(queueName, MQC.MQOO_INPUT_AS_Q_DEF + MQC.MQOO_FAIL_IF_QUIESCING)) {
    while (true) {
        MQMessage msg = new MQMessage();
        queue.Get(msg, new MQGetMessageOptions()); // <<= !!!IT IS DELAYED HERE!!!
        msg.Seek(0);
        string msgContent = msg.ReadString(msg.MessageLength);
        if (requestText.Equals(msgContent)) {
            break;
        }
    }
}

Thread Dumps:

• MQ Client Receiver Thread

SocketPal.Poll()
Socket.Poll()
MQTCPConnection.Receive() 
MQRcvThread.ReceiveBuffer()
MQRcvThread.ReceiveOneTSH()
MQRcvThread.Run()
ThreadHelper.ThreadStart_Context()
ExecutionContext.RunInternal()
ThreadHelper.ThreadStart()

Waits on Poll(), but it ends with 5 minute (heartbeat) timeout. Then it goes to this.network.Read() and immediately gets proper data.

    this.socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, this.timeout);
    if (this.socket.Poll(this.timeout * 1000, SelectMode.SelectRead))
    {
      length2 = this.network.Read(cBuffer, offset1, length1);

• Application Thread

Monitor.Wait()
MQSession.ExchangeTSH() 
MQProxyQueue.RequestMessages()
MQProxyQueue.FlushQueue()
MQProxyQueue.ProxyMQGET()
MQFAP.zstMQGET()
MQFAP.MQGET()
MQDestination.Get()
MQDestination.Get()
MqConnectionPoolTest.TestMqDirect()

Waits for entry.Reply to be filled by receive thread:

    while (entry.Reply == null) {
      Monitor.Wait((object) entry, this.rmtReqEntMaxPollTime, true);
      ...

Please, does anybody know a workaround or has a fix?

Answer 1

You should not Get and wait infinitely, you should do it like this:

const int TIMEOUTTIME = 20000;
try
{
    MQGetMessageOptions gmo = new MQGetMessageOptions();
    gmo.Options = MQC.MQGMO_WAIT;
    gmo.WaitInterval = TIMEOUTTIME;
    queue.Get(msg, gmo);
    msg.Seek(0);
    string msgContent = msg.ReadString(msg.MessageLength);
    if (requestText.Equals(msgContent)) {
        break;
    }
}
catch (MQException ex)
{
    if (ex.CompletionCode == MQC.MQCC_FAILED && ex.ReasonCode == MQC.MQRC_NO_MSG_AVAILABLE)
    {
        // Log on DEBUG level something like this:
        //    No message from <queue> after <TIMEOUTTIME / 1000> seconds, continue receiving");
        continue;
    }
    throw ex;
}

To make your programmer's life easier, I would recommend to use the XMS API.