IIS locking a file created by XMLWriter

Question

I've written a .Net Web API which takes it's inputs, parses them and then stores an XML file on a network share linked to our server. I have also built a Windows service which scans the network share for new files to process our business logic.

This works nearly 100% of the time, but very occasionally (1 in 20,000 times) IIS6 holds a lock on the file it creates and won't clear until IIS is restarted. The locked files are always 0 bytes.

Currently I have a file which has been locked for nearly 20 hours! Here is the code that creates the file:

    Try
        '-- Make sure the file doesn't already exist
        TempFileName = strFullFileName
        i = 1

        While IO.File.Exists(TempFileName)
            TempFileName = strFullFileName.Replace(".xml", "_" & i & ".xml")

            i += 1
        End While

        strFullFileName = TempFileName

        '-- Deserialise the message into a file
        drSerializer = New XmlSerializer(DetailsOfMsg.GetType)
        FS = New FileStream(strFullFileName, FileMode.Create, FileAccess.ReadWrite, FileShare.None)
        XW = XmlWriter.Create(FS)
        drSerializer.Serialize(XW, DetailsOfMsg)

    Finally
        Try : XW.Flush() : Catch : End Try
        Try : FS.Close() : Catch : End Try
        Try : XW.Close() : Catch : End Try
        FS = Nothing
        XW = Nothing
    End Try

Why is IIS still holding a lock?

Answer 1

Did you try to wrap the code within "Using" blocks? This ensures that types of FileStream and XmlWriter get disposed once the block's scope ends.

Answer 2

I think you need to separate this process. First create file on say folder X. Once created then move this file from folder X to shared location as there is watcher associated with this network share. Also, once file found then pick it and move to working folder and then start your business process on that file. 0 byte may be indicator of write and watch deadlock.

Answer 3

I can see that, you have created FileStream instance with FileShare = none, whereas your requirement says that, you need simultaneously read and write on shared location.

Correct code would be

FS = New FileStream(strFullFileName, FileMode.Create, FileAccess.ReadWrite, FileShare.ReadWrite)

FileShare - A constant that determines how the file will be shared by processes.

For more info - refer this - https://msdn.microsoft.com/en-us/library/5h0z48dh(v=vs.110).aspx

EDIT

From comment, I found that you need lock to be applied for Read operation, and the error you are getting ( not so frequently) might be because of write lock. To avoid this, you can use following.

FS = New FileStream(strFullFileName, FileMode.Create, FileAccess.ReadWrite, FileShare.Write)

FileShare.Write - Allows subsequent opening of the file for writing. If this flag is not specified, any request to open the file for writing (by this process or another process) will fail until the file is closed. However, even if this flag is specified, additional permissions might still be needed to access the file.