Emulate waiting on File.Open in C# when file is locked

Question

I have, essentially, the same problem as this poster, but in C#: Waiting until a file is available for reading with Win32

More information: we have code that calls File.Open in one of our projects, that occasionally dies when the file is already opened by another process (EDIT: or thread):

FileStream stream = File.Open(m_fileName, m_mode, m_access);
/* do stream-type-stuff */
stream.Close();

File.Open will throw an IOException (which is currently quietly swallowed somewhere), whose HResult property is 0x80070020 (ERROR_SHARING_VIOLATION). What I would like to do is this:

FileStream stream = null;
while (stream == null) {
    try {
        stream = File.Open(m_fileName, m_mode, m_access, FileShare.Read);
    } catch (IOException e) {
        const int ERROR_SHARING_VIOLATION = int(0x80070020);
        if (e.HResult != ERROR_SHARING_VIOLATION)
            throw;
        else
            Thread.Sleep(1000);
    }
}
/* do stream-type-stuff */
stream.Close();

However, HResult is a protected member of Exception, and cannot be accessed -- the code does not compile. Is there another way of accessing the HResult, or perhaps, another part of .NET I might use to do what I want?

Oh, one final caveat, and it's a doozy: I'm limited to using Visual Studio 2005 and .NET 2.0.

Note that the `HResult` property is [no longer `protected` as of .NET Framework v4.5](https://learn.microsoft.com/dotnet/api/system.exception.hresult#remarks): "Starting with the .NET Framework 4.5, the HResult property's setter is protected, whereas its getter is public. In previous versions of the .NET Framework, both getter and setter are protected." — Lance U. Matthews, May 04 '18 at 01:11

Igal Tabachnik · Accepted Answer · 2010-06-29T08:22:00.143

8

You can call Marshal.GetHRForException() within the catch clause to get the error code. No need for reflection:

using System.Runtime.InteropServices;

if (Marshal.GetHRForException(e) == ERROR_SHARING_VIOLATION)
    ....

edited Jun 29 '10 at 08:22

answered Jun 29 '10 at 07:17

Igal Tabachnik

31,174
15
92
157

Is this thread-safe? The code above is running in a thread; many threads will be attempting to call `File.Open` simultaneously. – Blair Holloway Jun 29 '10 at 07:38
I think you meant `System.Runtime.InteropServices`, BTW. :) – Blair Holloway Jun 29 '10 at 07:41
Never mind. MSDN states: "Any public static (Shared in Visual Basic) members of `[Marshal]` are thread safe. Any instance members are not guaranteed to be thread safe." – Blair Holloway Jun 29 '10 at 07:54
2

Actually, `Marshal.GetExceptionCode()` is wrong, now that I've seen it running. What I actually needed was `Marshal.GetHRForException(e)`. Do you mind updating your answer to accomodate? – Blair Holloway Jun 29 '10 at 08:11
Done! :) Can I get my 5 pts back? ;p – Igal Tabachnik Jun 29 '10 at 08:22

score 0 · Answer 2 · answered Jun 29 '10 at 07:08

0

Your best bet is using reflection unfortunately. Of course, since you sleep for 1sec between attempts, the performance costs will most likely go unnoticed.

answered Jun 29 '10 at 07:08

Blindy

65,249
10
91
131

Emulate waiting on File.Open in C# when file is locked

2 Answers2

Linked