C# .NET BackgroundWorker 6 FileSystemWatcher 该进程无法访问文件“PATH”，因为它正被另一个进程使用

Question

I'm trying to watch a directory for newly added files ending in .csv do something with them, delete the file and wait for a newly added file to do process the file again. I'm using a BackgroundService with the following code:

public class Worker : BackgroundService
{
    private readonly ILogger<Worker> _logger;
    private readonly IProcessFileService _processFileService;
    private ApplicationOptions _applicationOptions;
    private FileSystemWatcher _watcher = new();


    public Worker(ILogger<Worker> logger, IProcessFileService processFileService, IOptions<ApplicationOptions> applicationOptions)
    {
        _logger = logger;
        _processFileService = processFileService;
        _applicationOptions = applicationOptions.Value;
    }

    protected override Task ExecuteAsync(CancellationToken stoppingToken)
    {
        string filePath = _applicationOptions.InputDirectory;
        _watcher.Path = filePath;
        _watcher.EnableRaisingEvents = true;
        _watcher.NotifyFilter = NotifyFilters.FileName | NotifyFilters.CreationTime | NotifyFilters.LastWrite;
        _watcher.Filter = "*.csv*";
        _watcher.Created += new FileSystemEventHandler(OnFileCreated);
        return Task.CompletedTask;
    }

    private async void OnFileCreated(object sender, FileSystemEventArgs e)
    {
        if (e.ChangeType == WatcherChangeTypes.Created)
        {
            await HandleAddedFile();
        }     
    }

    private async Task HandleAddedFile()
    {
        try
        {
           await _processFileService.ProcessFile();
        }
        catch(Exception ex)
        {
            _logger.LogError("{error}", ex.Message);
        }
       _processFileService.DeleteFileAndLog();
    }
}

Works fine for the first time, but when trying inserting a second file in the directory, I get the error: The process cannot access the file "PATH" because it is being used by another process.

Processing the label includes some async work, how can I fix this issue?

Answer 1

I've followed the thread that Robert linked me; I had to rewrite some stuff, but I've got it to work now using the following code. I also had to modify some functions to take in the fullpath.

public class Worker : BackgroundService
{
    private readonly ILogger<Worker> _logger;
    private readonly IProcessFileService _processFileService;
    private ApplicationOptions _applicationOptions;
    private FileSystemWatcher _watcher = new();


    public Worker(ILogger<Worker> logger, IProcessFileService processFileService, IOptions<ApplicationOptions> applicationOptions)
    {
        _logger = logger;
        _processFileService = processFileService;
        _applicationOptions = applicationOptions.Value;
    }

    protected override Task ExecuteAsync(CancellationToken stoppingToken)
    {
        string filePath = _applicationOptions.InputDirectory;
        _watcher.Path = filePath;
        _watcher.EnableRaisingEvents = true;
        _watcher.NotifyFilter = NotifyFilters.FileName | NotifyFilters.CreationTime | NotifyFilters.LastWrite;
        _watcher.Filter = "*.csv*";
        _watcher.Created += new FileSystemEventHandler(OnFileCreated);
        return Task.CompletedTask;
    }

    private async void OnFileCreated(object sender, FileSystemEventArgs e)
    {
        if (e.ChangeType == WatcherChangeTypes.Created)
        {
            await HandleAddedFile(e);
        }     
    }

    static FileStream? WaitForFile(string fullPath, FileMode mode, FileAccess access, FileShare share)
    {
        for (int numTries = 0; numTries < 10; numTries++)
        {
            FileStream? fs = null;
            try
            {
                fs = new FileStream(fullPath, mode, access, share);
                return fs;
            }
            catch (IOException)
            {
                fs?.Dispose();
                Thread.Sleep(50);
            }
        }

        return null;
    }

    private async Task HandleAddedFile(FileSystemEventArgs e)
    {
        FileStream? fileStream = null;
        try
        {
           fileStream = WaitForFile(e.FullPath, FileMode.Open, FileAccess.Read, FileShare.Read);
           await _processFileService.ProcessFile(e.FullPath);
        }
        catch(Exception ex)
        {
            _logger.LogError("{error}", ex.Message);
        }
        fileStream?.Dispose();
       _processFileService.DeleteFileAndLog(e.FullPath);
    }
}