• 0

FileStream - The Process Cannot Access The File


Question

Hello, 

 

I have a file copying program and I have a custom class that utilizes a System.IO.FileSteam to copy a file to a destination computer.  For the most part it works quite well.  However I use it to copy to many remote locations.  Some of them have subpar network connections.  Every so often I'll get a server that has a unreliable network connection and it will momentarily drop off the network for a few seconds.  When this happens my FileStream breaks with the exception "The specified network name is no longer available.".  This is expected.

However the problem is after the program has waited 60 seconds it will retry the transfer.  The problem now is it can't even start because I get the error "The process cannot access the file '\\MyServer\c$\MyFile.zip' because it is being used by another process".  I'll continue to get this error indefinitely until I close the program and restart the transfer, then it is able to transfer once again.

It would appear that my source server still has a file handle open when this happens that's preventing the transfer again and closing the program releases it.  I would like to programically release the handle so I can restart the transfer automatically.

 

Here's what I've tried so far:

When the file transfer is started, I grab the FileSteam.SafeFileHandle to a variable.  When I get the above error, I've tried accessing SafeFileHandle.SetHandleAsInvalid(), SafeFileHandle.DangerousRelease() and SafeFileHandle.Close(), but I'll still get the file in use error when I retry.

12 answers to this question

Recommended Posts

  • 0

To replicate the problem, I imported my DLL into powershell.  I waited for the problem to occur.  I then grabbed the SafeFileHandle.  I first tried SetFileHandleAsInvalid() then retried.  Then I tried DangerousRelease().  Finally I tried Close(), but at that point I got "Exception calling "Close" with "0" argument(s): "Safe handle has been closed".

 

Also if I just call my handle variable it shows:   IsInvalid:  False, IsClosed:  True

  • 0
  On 13/03/2014 at 21:48, snaphat (Myles Landwehr) said:

Is the filestream locked? Closing a file that has outstanding locks is undefined according to the documentation.

 

Some how I never thought of that.  I always assumed that when I received an exception on a FileStream.Write(...) that the filestream was hosed then.  I adjusted my code as follows:

                try
                { m_Dest.Write(m_Buffer, 0, m_CurrentBlockSize); }
                catch (IOException ex)
                {
                    //  added the section below:
                    if (m_Dest.CanWrite)
                    {
                        try
                        { m_Dest.Close(); }
                        catch { }
                    }
                    // end new section
                    HadExceptionWhileCopying(ex, true);
                    return;
                }

So far it worked in my test environment.  Will see if it works in production tomorrow.

Thanks Myles!

  • 0

^ yeah the filestream may still be valid and be locked. For that matter, it could technically be still not working (in terms of communication), but it could still be marked as locked. I was thinking of calling unlock() when I posted my response. I'm not sure why the above code would work given that canWrite should just give you the state of whether the stream is closed or not and if you call close() on an already closed stream it should work fine.

  • 0
  On 15/03/2014 at 00:06, stumper66 said:

My above solution worked.

 

I dug through my existing code and it was supposed to call a close on the filestream  in the event of an error but due to a flaw in my logic it never got called.

I see, that definitely fits the bill for the error you were getting!

  • 0
  On 15/03/2014 at 00:28, notchinese said:

Is it feasible given the code design to just wrap the filestream in a using() {} block?

 

"using" is an assurance that Dispose() will be called to free resources. It doesn't necessarily call Close(). try...finally would do that.

  • 0
  On 21/03/2014 at 12:54, Eric said:

"using" is an assurance that Dispose() will be called to free resources. It doesn't necessarily call Close(). try...finally would do that.

Yes it does. http://stackoverflow.com/questions/911408/does-stream-dispose-always-call-stream-close-and-stream-flush

 

In general, if an object implements Dispose() then you can expect that calling that is enough to clean it up properly, whatever the state it was in.

 

Also, using actually expands to try-finally so it's strictly equivalent, if all you're doing in the finally clause is to call Dispose().

  • 0
This topic is now closed to further replies.
  • Posts

    • From what I understand, RAID 1 makes a copy of one disk. How does it do this? If something happened to one drive, could I take the other one out, plug it into a PC and use it like a normal disk? I have two hard drives that have the same information on - a bit of protection if one drive fails. But I've just been manually copying the data twice.
    • Microsoft SharePoint gets Modern Page Templates to speed up page creation by Paul Hill SharePoint, Microsoft’s enterprise content management solution that allows organizations to set up internal pages and share documents, has just got a big update with the new Modern Page Templates. Microsoft said that it’s going to be rolling out the feature to customers globally between early July and early August. Organization members that want to set up pages on SharePoint using the new templates can do so from multiple entry points including the Site Home (the home of a Communication or Teams site), App Bar (the persistent navigation pane on the left of SharePoint), and the New Web Part (a webpart that displays and creates news posts directly on pages). By giving colleagues multiple access points to the new templates, there’s more chance they’ll be found and used. By including plenty of swanky templates, Microsoft is making it so you can spend less time designing pages, and more time filling them with content that really matters. If you want to create a new page using the templates, just go to New > Page and select a template “From Microsoft”. If you were making a news post, you would go to New > News post then you’d be presented with the new Template Gallery where you can select a custom template created by your colleagues under “Saved on this site”. While these new templates are coming to customers globally next month, Microsoft is already busy working on new features to make templates easier to discover and make them more useful. For example, it is building tenant-wide custom templates that can be published across sites for organization-wide use, and it’s working on Copilot templates that you can use when creating pages with Copilot. Neither of these features was given a release timeline. Customers won’t need to do anything to start using Modern Page Templates as they’ll be available automatically as it rolls out worldwide across tenants. For those who want to dive deeper, Microsoft will be publishing additional documentation and guidance about this feature soon.
    • Times are changing: https://arstechnica.com/gaming...ndows-11-ars-testing-finds/
    • Unless there is “bug” that all of a sudden sends your messages to Meta. Where have I heard this before?!
    • Maybe, just maybe... and it isn't you... there are some people who like the Windows 11 UI (for whatever reason) and want a better backend.
  • Recent Achievements

    • One Month Later
      Leonard grant earned a badge
      One Month Later
    • Week One Done
      pcdoctorsnet earned a badge
      Week One Done
    • Rising Star
      Phillip0web went up a rank
      Rising Star
    • One Month Later
      Epaminombas earned a badge
      One Month Later
    • One Year In
      Bert Fershner earned a badge
      One Year In
  • Popular Contributors

    1. 1
      +primortal
      539
    2. 2
      ATLien_0
      205
    3. 3
      +FloatingFatMan
      168
    4. 4
      Michael Scrip
      150
    5. 5
      Som
      126
  • Tell a friend

    Love Neowin? Tell a friend!