How to Ensure File Completion Before Copying to Prevent 'File in Use' Errors?

Ensuring File Completion Before Copying

In the scenario where a FileSystemWatcher is used to detect the creation of files in a directory and subsequently copy them to a different location, an issue arises when large files (>10MB) are involved. The error "Cannot copy the file, because it's used by another process" may be encountered due to the copying process starting before the file creation is complete.

Workaround:

The only known workaround involves checking whether the file is locked before initiating the copy operation. This can be achieved through a function that repeatedly checks if the file is in use until it returns false, indicating that the file is no longer locked.

Method 1 (Direct Copy):

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

    try
    {
        stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None);
    }
    catch (IOException)
    {
        // File still being written, processed, or doesn't exist
        return true;
    }
    finally
    {
        if (stream != null)
            stream.Close();
    }

    // File not locked
    return false;
}

Method 2:

const int ERROR_SHARING_VIOLATION = 32;
const int ERROR_LOCK_VIOLATION = 33;
private bool IsFileLocked(string file)
{
    // Check destination file status
    if (File.Exists(file))
    {
        FileStream stream = null;
        try
        {
            stream = File.Open(file, FileMode.Open, FileAccess.ReadWrite, FileShare.None);
        }
        catch (Exception ex2)
        {
            int errorCode = Marshal.GetHRForException(ex2) & ((1 << 16) - 1);
            if ((ex2 is IOException) && (errorCode == ERROR_SHARING_VIOLATION || errorCode == ERROR_LOCK_VIOLATION))
            {
                return true;
            }
        }
        finally
        {
            if (stream != null)
                stream.Close();
        }
    }
    return false;
}

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