长期运行的WCF服务即将终止的原因是什么？

Question

I have a long-running WCF service, hosted in IIS, that handles printing without any user interaction. After about 2 hours of looping through 1000 print jobs, the WCF service just seems to die. The log file I track indicates that the last print job was sent to the printer, but it never returns success nor failure (again, according to the log file).

From the log file, it would normally say:

2015-12-17 19:00:23,673 [27] INFO Barn.WCF.SysPrsPrintServer - Sending Print Job... PrintDocumentId=168;PrintSectionId=742;CustomerId=112702;DeliveryAddressId=474984;DocumentName=/SystemProcesses/Reports/CertificateOfRegistry;PrinterLocation=HB-MFP1;PrinterPaperSource=Cassette 3

2015-12-17 19:00:32,626 [27] INFO Barn.WCF.SysPrsPrintServer - PdfPrintHandler.Print: Printer HB-MFP1 indicates the print job is complete.

But the last log file entry is:

2015-12-17 19:00:32,688 [27] INFO Barn.WCF.SysPrsPrintServer - Sending Print Job... PrintDocumentId=169;PrintSectionId=742;CustomerId=112702;DeliveryAddressId=474984;DocumentName=/SystemProcesses/Reports/CertificateOfRegistry;PrinterLocation=HB-MFP1;PrinterPaperSource=Cassette 3

Can you see how this might be possible that I get no message back at all? Is it possible the WCF service just died or IIS recycled the app pool or something like that? So without further ado, here is my class:

using System;
using System.Collections.Generic;
using System.Drawing.Printing;
using System.IO;
using System.Threading;
using log4net;
using Aspose.Pdf.Facades;

namespace Barn.API.Print.PrintHandlers
{
    public class PdfPrintHandler
    {
        private const int LargePdfByteCount = 3000000;
        private readonly ILog _log;
        private readonly ManualResetEvent _resetEvent = new ManualResetEvent(false);

        public PdfPrintHandler(ILog log)
        {
            _log = log;

            var license = new Aspose.Pdf.License();
            var pathLicense = AppDomain.CurrentDomain.SetupInformation.ApplicationBase + "bin\\Aspose.Pdf.lic";
            license.SetLicense(pathLicense);
        }

        /// <summary>
        /// Prints the specified stream.
        /// </summary>
        /// <param name="stream">The stream.</param>
        /// <param name="printerSettings">The printer settings.</param>
        /// <param name="pageSettings">The page settings.</param>
        /// <param name="timeout">The timeout.</param>
        /// <param name="errors"></param>
        /// <returns>The status of the print job.</returns>
        public PrintJobStatusEnum Print(Stream stream, PrinterSettings printerSettings, PageSettings pageSettings, PrintDocumentModel printJob, int timeout, out List<string> errors)
        {

            errors = new List<string>();

            // Reset the wait handler to make sure the event is not signaled
            _resetEvent.Reset();

            // Set attributes for printing
            var viewer = new PdfViewer
            {
                AutoResize = true, 
                AutoRotate = true, 
                PrintPageDialog = false,
                PrintAsImage = false
            };

            // Add an event listener when print job sent to printer
            viewer.EndPrint += ViewerOnEndPrint;

            //Print document using printer and page settings
            try
            {
                _log.InfoFormat("Sending Print Job... PrintDocumentId={0};PrintSectionId={1};CustomerId={2};DeliveryAddressId={3};DocumentName={4};PrinterLocation={5};PrinterPaperSource={6}",
                    printJob.PrintDocumentId, 
                    printJob.PrintSectionId != null ? printJob.PrintSectionId.ToString() : "null", 
                    printJob.CustomerId != null ? printJob.CustomerId.ToString() : "null", 
                    printJob.DeliveryAddressId != null ? printJob.DeliveryAddressId.ToString() : "null", 
                    printJob.DocumentName != null ? printJob.DocumentName : "null", 
                    printJob.PrinterLocation != null ? printJob.PrinterLocation : "null",
                    pageSettings.PaperSource.SourceName != null ? pageSettings.PaperSource.SourceName : "null");

                // Print
                if (stream.Length <= LargePdfByteCount)
                {
                    // Bind the stream then print
                    viewer.BindPdf(stream);
                    viewer.PrintDocumentWithSettings(pageSettings, printerSettings);
                }
                else
                {
                    // Use a more efficient printing method with larger documents
                    viewer.PrintLargePdf(stream, pageSettings, printerSettings);
                }

                // Block until the event finishes or timeout reached
                _resetEvent.WaitOne(TimeSpan.FromMinutes(timeout));

                // Check the print status
                if (viewer.PrintStatus != null)
                {
                    // An exception was thrown
                    var ex = viewer.PrintStatus as Exception;
                    if (ex != null)
                    {
                        // Get exception message
                        _log.Error("PdfPrintHandler.Print: Print Error: " + ex.Message + ex.StackTrace, ex);
                        errors.Add(ex.Message);
                    }
                    return PrintJobStatusEnum.Error;
                }
                else
                {
                    // No errors were found. Printing job has completed successfully
                    _log.InfoFormat("PdfPrintHandler.Print: Printer {0} indicates the print job is complete.", printerSettings.PrinterName);
                    return PrintJobStatusEnum.Printed;
                }
            }
            catch (Exception e)
            {
                _log.Error("PdfPrintHandler.Print Exception: " + e.Message + e.StackTrace, e);
                errors.Add(e.Message);
            }
            finally
            {
                viewer.Close();
            }

            return PrintJobStatusEnum.Error;
        }

        private void ViewerOnEndPrint(object sender, PrintEventArgs printEventArgs)
        {
            // Signal the event is finished
            _resetEvent.Set();
        }
    }
}

WCF Service Interface:

using System.ServiceModel;

namespace Barn.WCF
{
    // NOTE: You can use the "Rename" command on the "Refactor" menu to change the interface name "ISysPrsPrintServer" in both code and config file together.
    [ServiceContract]
    public interface ISysPrsPrintServer
    {
        [OperationContract]
        string DoWork(string data);
    }
}

Answer 1

Here it is in the Windows event log:

A worker process with process id of '3236' serving application pool 'testws.mydomain.ca' was shutdown due to inactivity. Application Pool timeout configuration was set to 20 minutes. A new worker process will be started when needed.

So IIS seems to have thought that there was 20 minutes of inactivity because the WCF service is called asynchronously. The process is working away, but IIS decided to recycle the application pool in the middle of the process running.

I changed the settings in IIS on the application pool according to this: https://serverfault.com/questions/333907/what-should-i-do-to-make-sure-that-iis-does-not-recycle-my-application

Answer 2

I would suggest checking the operation contracts of your print methods. I have seen WCF services fail out when the isOneWay attribute is not set or is set to false on a void method. try something like this

    [OperationContract(IsOneWay=true)]
    public void PrintDocumentWithSettings(PageSettings settings, PrinterSettings settings);