How to implement "retry/abort" mechanism for writing files that may be used by another process?

Question

This is really short question. I don't understand try-catch mechanism completely.

This is my current code:

public static void WriteText(string filename, string text)
{
    try
    {
        System.IO.StreamWriter file = new System.IO.StreamWriter(filename);
        file.Write(text);
        file.Close();
    }
    catch(Exception exc)
    {
        MessageBox.Show("File is probably locked by another process.");
    }
}

Background:

Im writing application that shares configuration files with another application.

I need some dialog messagebox with "retry" and "abort" buttons, when that file is used by other application. When that message will appear - I will close that other application and I will try to rewrite that file again by pressing "Retry" button.

The question is too short. Describe the runtime environment of this code. — Hans Passant, Sep 09 '13 at 18:33
So just display a message box with yes/no/cancel in the catch clause. — Hans Passant, Sep 09 '13 at 18:41
You should wrap your writer in a `using` to ensure that the file handle is released even if there is an exception. That or just use `File.WriteAllText` instead, which will handle it for you. — Servy, Sep 09 '13 at 18:43

Adriaan Stander · Answer 1 · 2013-09-09T18:42:13.247

4

Whatr we have is using a counter for re-tries and possibly a thread sleep.

So something like

int tries = 0;
bool completed = false;
while (!completed)
{
    try
    {
        System.IO.StreamWriter file = new System.IO.StreamWriter(filename);
        file.Write(text);
        file.Close();
        completed = true;
    }
    catch(Exception exc)
    {
        tries++;
        //You could possibly put a thread sleep here
        if (tries == 5)
            throw;
    }
}

edited Sep 09 '13 at 18:42

answered Sep 09 '13 at 18:35

Adriaan Stander

162,879
31
289
284

This is really the accepted approach. You simply put your try-catch inside a loop with a retry counter. You suppress the exception until the retries have all been consumed, after that you throw. – evanmcdonnal Sep 09 '13 at 18:40
I need more time to close application that may use my file. – Kamil Sep 09 '13 at 18:41
I got it. I will put messagebox with question instead of thread sleep. – Kamil Sep 09 '13 at 18:58

score 2 · Accepted Answer · edited Mar 07 '18 at 02:16

Even though there's a good answer already I'll submit one that's more tuned towards the OP's question (let the user decide instead of using a counter).

public static void WriteText(string filename, string text)
{
    bool retry = true;
    while (retry)
    {
         try
         {
              System.IO.StreamWriter file = new System.IO.StreamWriter(filename);
              file.Write(text);
              file.Close();
              retry=false;
          }
          catch(Exception exc)
          {
                MessageBox.Show("File is probably locked by another process.");
                // change your message box to have a yes or no choice
                // yes doesn't nothing, no sets retry to false
          }
    }
}

If you need more info on how to implement the messagebox check out the following links;

http://msdn.microsoft.com/en-us/library/0x49kd7z.aspx

MessageBox Buttons?

Thanks. I think I know how to use MessageBox with customized buttons. This is exactly what I need. — Kamil, Sep 09 '13 at 18:55

score 1 · Answer 3 · answered Sep 09 '13 at 18:43

1

I would do it like that:

 public static void WriteText(string filename, string text, int numberOfTry = 3, Exception ex = null)
    {
        if (numberOfTry <= 0)
            throw new Exception("File Canot be copied", ex);
        try
        {
            var file = new System.IO.StreamWriter(filename);
            file.Write(text);
            file.Close();
        }
        catch (Exception exc)
        {
            WriteText(filename,text,--numberOfTry,ex);
        }
    }

answered Sep 09 '13 at 18:43

Bassam Alugili

16,345
7
52
70

1

Why do you pass exception and never use it? – Sriram Sakthivel Sep 09 '13 at 18:45
Never suppress an Exception this will be anti pattern but he can do throw the same Exception throw ex this will be better because throwing Exception class to generic and also anti pattren – Bassam Alugili Sep 09 '13 at 18:49
1

If so you're swallowing first two exceptions if any. IMO `Aggregateexception` is better here – Sriram Sakthivel Sep 09 '13 at 18:51

maf-soft · Answer 4 · 2015-10-21T14:20:11.663

I like it more like this (example tries to save a RichTextBox on close and allows retrying save or aborting close):

protected override void OnClosing(CancelEventArgs e)
{
    if (richTextBox_Query.Modified)
    {
        DialogResult result;
        do
            try
            {
                richTextBox_Query.SaveFile(
                    Path.ChangeExtension(Application.ExecutablePath, "sql"),
                    RichTextBoxStreamType.UnicodePlainText);
                result = DialogResult.OK;
                richTextBox_Query.Modified = false;
            }
            catch (Exception ex)
            {
                result = MessageBox.Show(ex.ToString(), "Exception while saving sql query",
                    MessageBoxButtons.AbortRetryIgnore);
                e.Cancel = result == DialogResult.Abort;
            }
        while (result == DialogResult.Retry);
    }

    base.OnClosing(e);
}

How to implement "retry/abort" mechanism for writing files that may be used by another process?

4 Answers4