LockCheck

Uses platform APIs to find processes locking one or multiple files.

Builds

Platforms

Windows

On the Windows platform there are two possible engines to provide the lock information:

Windows RestartManager API (default)
NTDLL functions (using LockManagerFeatures.UseLowLevelApi)

The RestartManager API has the advantage of being a documented interface, but the disadvantage that it might introduce a rather big overhead. For example, The backing RmRegisterResources Win32-API is rather expensive.

Since the "who locks the file" information is potentially highly volatile, and the locking processing might already be gone when you start looking for it using this library after you got an exception, this might be too much. YMMV.

Also note, that the RestartManager can only have a maximum of 64 restart manager sessions per user session - this might not be a real world issue, as the API is usually only used by installers and setup applications, but again, YMMV.

Linux

On Linux, the /proc/locks file is used as basis for finding processes holding a lock on a file. Linux supports multiple lock types (see this article for an overview). Not all those lock types are directly associated with a single process, so the ProcesInfo.ProcessID member can be -1 here. Additionally, on Linux, the ProcessInfo.LockType, ProcessInfo.LockMode and ProcessInfo.LockAccess properties return the respective values. These properties are null on Windows.

Linux support should be considered experimental. Albeit the Unit-Tests and example application works, it has not been used in a real world scenario. The Linux version has been developed on WSL2.

If you have any improvements / PRs please let me know.

Usage

Getting lock information on demand

To get the lockers of a file, if any, use the LockManager.GetLockingProcessInfos() function.

foreach (var processInfo in LockManager.GetLockingProcessInfods("c:\\temp\\foo.xlsx"))
{
    // Do something with the information.
}

Enriching Exceptions with Lock Information

The method ExceptionUtils.RethrowWithLockingInformation() can be used to enrich exceptions with lock information, if available.

Here is a phony example. The inner Open call causes an IOException, because the outer Open call already opened the file exclusively (albeit in the same process, but that doesn't matter for the cause of the example):

static void Test()
{
    using (var file = File.Open("c:\\temp\\foo.txt", FileMode.OpenOrCreate, FileAccess.ReadWrite))
    {
        try
        {
            var file2 = File.Open("c:\\temp\\foo.txt", FileMode.Open, FileAccess.ReadWrite);
        }
        catch (Exception ex)
        {
            if (!ex.RethrowWithLockingInformation("C:\\temp\\foo.txt"))
                throw;
        }
    }
}

If the RethrowWithLockingInformation() method could deduce any lockers, it will create an IOException that has the original exception as inner exception, but additionally includes lock information in the message text.

If the RethrowWithLockingInformation() method could not deduce any lockers or the original exception did not signify a locking/sharing violation, it will return false and NOT raise any exception. In this case, as show above, you should simply rethrow the original exception.

A view notes:

Getting the lockers, if any, is of course a matter of timing. By the time you got the original exception and your code comes around to determine them, they might already be gone.
Currently, this is not an all purpose solution, because you need to know the original file- or directory name in question.
Performance could be an issue. It is comparatively expensive to determine the lockers - albeit you might argue that when the error happens performance is not so much an issue anymore.

Personally, I use this helper only in situations where I know locking issues are "common", for example when attempting to recursively delete a directory tree, etc.

Finally, here is the exception output without the RethrowWithLockingInformation() call:

 System.IO.IOException: The process cannot access the file 'C:\temp\foo.txt' because it is being used by another process.
    at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
    at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, ...
    at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share)
    at System.IO.File.Open(String path, FileMode mode, FileAccess access)
    ExceptionUtils.cs(25,0): at LockCheck.ExceptionUtils.Test()

And this is it, with that information included:

System.IO.IOException: The process cannot access the file 'C:\temp\foo.txt' because it is being used by another process.
File C:\temp\foo.txt locked by: [MyApp 1.0.0.0, pid=18860, user=cklutz started=2017-07-16 12:28:57.714]
   ---> System.IO.IOException: The process cannot access the file 'C:\temp\foo.txt' because it is being used by another process.
    at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
    at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, ...
    at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share)
    at System.IO.File.Open(String path, FileMode mode, FileAccess access)
    ExceptionUtils.cs(20,0): at LockCheck.ExceptionUtils.Test()
   --- End of inner exception stack trace ---
    ExceptionUtils.cs(80,0): at LockCheck.ExceptionUtils.RethrowWithLockingInformation(Exception ex, String[] fileNames)
    ExceptionUtils.cs(24,0): at LockCheck.ExceptionUtils.Test()

Examples

Two example identical example applications are included: one for .NET Framework 4.7.2+ and one for .NET Core 3.1+.

You can test the functionality as follows:

Open/create a file "C:\temp\foo.xlsx" in Microsoft Excel - you can use any other application that actually locks a file, of course.
Run the following command:

Test.NetFx.exe c:\temp\foo.xlsx

The ouput should be like

Process ID        : 1296
Process Start Time: Saturday, 24th October 2015 16:17:58
Application Type  : MainWindow
Application Status: Running
Application Name  : Microsoft Excel
TS Session ID     : 1

cklutz / LockCheck

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