Question

评论决议：
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，它仍会在使用行中使用IOException崩溃应用程序（写入程序不会发生这种情况）。

我也将捕获量设为catch (IOException ...，我认为它没有区别，只是让它更具可读性。

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，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（作者和读者都使用FileShare.None）所以基本上我正在处理异常直到文件可用，但无效。

Answer 1

以下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...");
    }
);

Answer 2

我使用Is there a global named reader/writer lock?中的信息完成了此操作。

我认为结果有点像ReaderWriterLockSlim，它适用于多个进程而非线程正在访问资源的情况。

Answer 3

您可以使用互斥对象来保护共享资源免受多个线程或进程的同时访问。

Answer 4

您可以通过编写如下函数来检查文件锁定：

protected bool IsFileLocked(FileInfo file)
{
    FileStream stream = null;

    try
    {
        stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None);
    }
    catch (IOException)
    {
        //the file is unavailable because it is:
        //still being written to
        //or being processed by another thread
        //or does not exist (has already been processed)
        return true;
    }
    finally
    {
        if (stream != null)
            stream.Close();
    }

    //file is not locked
    return false;
}

Answer 5

Timwi的回答帮助了我们很多（虽然在另一个上下文中）但我发现如果你想从所有IOExceptions中获取HResult，还需要添加标志“BindingFlags.Public”：

public static int GetHresult(this IOException ex)
{
   return (int)ex.GetType().GetProperty("HResult", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance).GetValue(ex, null);
}

Answer 6

使用阅读器＆amp;作家锁正确的catch语法

catch(Exception e)

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(Exception e)
    {
        // bla bla bla does not matter again
    }
    Thread.Sleep(500);
}

文件锁定时避免崩溃？

6 个答案: