WCF服务-队列和批处理消息（通过SMTP发送电子邮件）

Question

I have a WCF Service working via named pipes that is receiving data from ASP.NET MVC application:

[ServiceContract]
public interface IEmailProcessor
{
    [OperationContract(AsyncPattern = true)]
    void SendEmails(string subject, string body, string from, string to);
}

Service gets subject, body, sender and recipients of an email. Then it puts an email together and send via SMTP.

Client (MVC applicataion) is sending several emails at once, so I would like the service itself to work asynchronously (client just invokes SendEmails method few times and then the WCF Server takes care of the rest). But my email server sometimes refuses to send email because of greylisting of new email addresses. That's why I would like the WCF Server to also queue those email and try to send them one by one (retry few times if the error occurs).

I've read several topics on WCF async nad MSMQ methods, but what is the best approach in my situation? Should I create two WCF Services (client-server & server-server)? Or maybe use multi-threading? It's also important for me to not use any built-in SMTP solution because I would like to expand my Service to handle other messages not only emails.

Answer 1

For exactly the same requirement I've made this whole Email solution for my self however I did not use the MSMQ queue.

following are the steps

1. Create Asynchronous WCF web service
2. Use Task await async technique to run the send email thread inside service using task.run(()=>AsyncSendEmail)
3. skip through on all smptpexception on try catch and run sp to update table field isEmailSent= false in case of error
4. subscribe the web servive through client "yourwebapplication"
5. invoke service by doing task.factory.startNew(()=> proxy.sendEmail(paramters))

6. create a simple windows task scheduler task to invoke to run service on scheduled time period to retry sending emails Simple Window Task Schedular

7. To read no deliver, failure email Emails from your exchange account I used third party service component Admin System Software and update table fields isDelivered=No , ErrorDescription=errorDesc

Hope this solution helps you..

Shaz

Answer 2

I followed zaitsman's suggestion and created queue inside the service using ConcurrentQueue . I also used this example of creating new Thread: http://msdn.microsoft.com/en-us/library/7a2f3ay4%28v=vs.80%29.aspx

I added new Thread to my WCF Server:

    var thread = new Thread(EmailThread.Instace.DoWork);
    thread.Start();

And then SendEmails method in my Service uses Enqueue to add msg to the ConcurrentQueue .

    public void SendEmails(string from, string to, string subject, string body)
    {
        var msg = new MailMessage(from, to, subject, body)
        {
            IsBodyHtml = true,
            BodyEncoding = Encoding.UTF8,
            DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure
        };

        EmailThread.Instace.Messages.Enqueue(msg);
    }

And here is EmailThread class that is doing it's work in the background (ie. accepting new emails to the queue and sequentially dequeuing them.

internal class EmailThread
{
    //Ensure that only one instance of EmailThread can exist
    private static readonly EmailThread Instance = new EmailThread();
    public static EmailThread Instace { get { return Instance; } }

    //Here is our Queue
    public ConcurrentQueue<MailMessage> Messages { get; private set; }

    private EmailThread()
    {
        Messages = new ConcurrentQueue<MailMessage>();
    }

    // This method is called when the thread is started and repeated once a 10 seconds
    public void DoWork()
    {
        while (!_shouldStop)
        {
            Console.WriteLine("email sender thread: working...");

            if (!Messages.IsEmpty)
            {
                //define SMTP credentials here
                var smtp = new SmtpClient()

                var failed = new Queue<MailMessage>();

                MailMessage message;
                while (Messages.TryDequeue(out message))
                {
                    try
                    {
                        smtp.Send(message);
                        Console.WriteLine("email sender thread: successfully sent email...");
                    }
                    catch (SmtpException)
                    {
                        //Enqueue again if failed
                        failed.Enqueue(message);
                        Console.WriteLine("email sender thread: error sending email, enqueuing...");
                    }
                }

                foreach (var mailMessage in failed)
                {
                    Messages.Enqueue(mailMessage);
                }

                smtp.Dispose();
            }
            Thread.Sleep(10000);
        }
        Console.WriteLine("email sender thread: terminating gracefully.");
    }
    public void RequestStop()
    {
        _shouldStop = true;
    }
    // Volatile is used as hint to the compiler that this data
    // member will be accessed by multiple threads.
    private volatile bool _shouldStop;

}