文件锁定时避免崩溃？

Question

评论解决:
应用程序崩溃是由另一个问题引起的

我正在读取/写入来自2个不同应用程序的文件,当正在读取或写入文件时,它将始终被应用程序A或B锁定,并且它们都使用FileShare.None.

我的问题是,即使将读者包装在try/catch中,它仍然会在使用行中使用IOException崩溃应用程序(写入程序不会发生).

我也做了catch (IOException ...我认为没有区别的捕获,然后让它更具可读性.

在文件被锁定时忽略的正确方法是什么,并在文件可用之前继续尝试？

while (true)
{
    try
    {
        using (FileStream stream = new FileStream("test_file.dat", FileMode.Open, FileAccess.Read, FileShare.None))
        {
            using (TextReader reader = new StreamReader(stream))
            {
                // bla bla bla does not matter
            }
        }
    }
    catch
    {
        // bla bla bla does not matter again
    }
    Thread.Sleep(500);
}

写

private bool WriteData(string data)
{
    try
    {
        using (FileStream stream = new FileStream("test_file.dat", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None))
        {
            stream.SetLength(0);
            using (TextWriter writer = new StreamWriter(stream))
            {
                writer.Write(data);
            }
        }
        return true;
    }
    catch
    {
        return false;
    }
}

请注意,FileShare.None当文件被用于读取或写入的任何过程时,我不会向任何人提供共享权(编写者和读者都使用),所以基本上我正在处理异常,直到文件可用无效.

Answer 1

这是我们为此目的使用的代码.

/// <summary>
/// Executes the specified action. If the action results in a file sharing violation exception, the action will be
/// repeatedly retried after a short delay (which increases after every failed attempt).
/// </summary>
/// <param name="action">The action to be attempted and possibly retried.</param>
/// <param name="maximum">Maximum amount of time to keep retrying for. When expired, any sharing violation
/// exception will propagate to the caller of this method. Use null to retry indefinitely.</param>
/// <param name="onSharingVio">Action to execute when a sharing violation does occur (is called before the waiting).</param>
public static void WaitSharingVio(Action action, TimeSpan? maximum = null, Action onSharingVio = null)
{
    WaitSharingVio<bool>(() => { action(); return true; }, maximum, onSharingVio);
}

/// <summary>
/// Executes the specified function. If the function results in a file sharing violation exception, the function will be
/// repeatedly retried after a short delay (which increases after every failed attempt).
/// </summary>
/// <param name="func">The function to be attempted and possibly retried.</param>
/// <param name="maximum">Maximum amount of time to keep retrying for. When expired, any sharing violation
/// exception will propagate to the caller of this method. Use null to retry indefinitely.</param>
/// <param name="onSharingVio">Action to execute when a sharing violation does occur (is called before the waiting).</param>
public static T WaitSharingVio<T>(Func<T> func, TimeSpan? maximum = null, Action onSharingVio = null)
{
    var started = DateTime.UtcNow;
    int sleep = 279;
    while (true)
    {
        try
        {
            return func();
        }
        catch (IOException ex)
        {
            int hResult = 0;
            try { hResult = (int) ex.GetType().GetProperty("HResult", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(ex, null); }
            catch { }
            if (hResult != -2147024864) // 0x80070020 ERROR_SHARING_VIOLATION
                throw;
            if (onSharingVio != null)
                onSharingVio();
        }

        if (maximum != null)
        {
            int leftMs = (int) (maximum.Value - (DateTime.UtcNow - started)).TotalMilliseconds;
            if (sleep > leftMs)
            {
                Thread.Sleep(leftMs);
                return func(); // or throw the sharing vio exception
            }
        }

        Thread.Sleep(sleep);
        sleep = Math.Min((sleep * 3) >> 1, 10000);
    }
}

使用示例:

Utilities.WaitSharingVio(
    action: () =>
    {
        using (var f = File.Open(file, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None))
        {
            // ... blah, process the file
        }
    },
    onSharingVio: () =>
    {
        Console.WriteLine("Sharing violation. Trying again soon...");
    }
);