问LockFileEX在C#中的应用

EN

    private const uint LOCKFILE_EXCLUSIVE_LOCK = 0x00000002;
    private static readonly Action WinIOError;

    static Win32Native()
    {
        BindingFlags bindingAttr = BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic;
        var winIOErrorMethod = typeof(string).Assembly.GetType("System.IO.__Error").GetMethod("WinIOError", bindingAttr, null, Type.EmptyTypes, null);
        WinIOError = (Action)Delegate.CreateDelegate(typeof(Action), winIOErrorMethod);
    }

    public static void LockFile(SafeFileHandle handle, bool exclusive, long offset, long length, Action action)
    {
        if (handle == null)
            throw new ArgumentNullException("handle");
        if (handle.IsInvalid)
            throw new ArgumentException("An invalid file handle was specified.", "handle");
        if (offset < 0)
            throw new ArgumentOutOfRangeException("The offset cannot be negative.", "offset");
        if (length < 0)
            throw new ArgumentOutOfRangeException("The length cannot be negative.", "length");
        if (action == null)
            throw new ArgumentNullException("action");

        LockFileUnsafe(handle, exclusive, offset, length, action);
    }

    private static unsafe void LockFileUnsafe(SafeFileHandle handle, bool exclusive, long offset, long length, Action action)
    {
        Overlapped overlapped = new Overlapped();
        overlapped.OffsetHigh = (int)(offset >> 32);
        overlapped.OffsetLow = (int)offset;

        IOCompletionCallback callback =
            (errorCode, numBytes, nativeOverlapped) =>
            {
                try
                {
                    action();
                }
                finally
                {
                    Overlapped.Free(nativeOverlapped);
                }
            };

        NativeOverlapped* native = overlapped.Pack(callback, null);
        uint flags = exclusive ? LOCKFILE_EXCLUSIVE_LOCK : 0;
        if (!LockFileEx(handle, flags, 0, (int)length, (int)(length >> 32), native))
        {
            Overlapped.Free(native);
            WinIOError();
        }
    }

    [DllImport("kernel32.dll", SetLastError = true)]
    private static unsafe extern bool LockFileEx(SafeFileHandle handle, uint flags, uint mustBeZero, int countLow, int countHigh, NativeOverlapped* overlapped);