c# - Make a BackgroundWorker do several operations sequentially without freezing the form

Question

I have already asked a somwhat similar question here but I now have a follow-up question.

I need to launch the external program several times in a row, but I have several problems with it :

• It tried to simultaneously launch all the operations. I have put an empty "while (bgwkSVN.IsBusy) { }", it kinda works, but I'm pretty sure it will make some of you cry a little.
• It still freezes the form as long as all the operations are not completed. Given a few other SO topics, I think the way my code is written, the application isn't really multithreaded, or I don't take advantage of it... but I'm really not familiar with threading.
• It doesn't seems to do what I ask it to do. I shall try with a more simple operation, to see if the operation doesn't succeeds, or if the backgroundworker is never launched.

Here is the code (sorry, it's kinda long) :

private struct svnCommand
{
    public svnCommand(string args, string path, int pourcent)
    {
        this.args = args;
        this.path = path;
        this.pourcent = pourcent;
    }
    public string args;
    public string path;
    public int pourcent;
}

private BackgroundWorker bgwkSVN;

public Merger()
{
    InitializeComponent();
    InitializeBackgroundWorker();
    this.textBoxCheminRacine.Text = cheminRacine;
}

private void MergerRevisions(object sender, EventArgs e)
{

    activerControles(false);

    textBoxOutput.Text = "";
    cheminRacine = textBoxCheminRacine.Text;
    if (!cheminRacine.EndsWith("")) { cheminRacine = cheminRacine + ""; }

    string branchToMerge = this.textBoxBranche.Text;
    if (branchToMerge.StartsWith("/")) { branchToMerge = branchToMerge.Substring(1); }

    // révision(s)
    string revisions = "";
    foreach (string r in textBoxRevision.Text.Split(','))
    {
        int rev;
        if (int.TryParse(r, out rev))
        {
            revisions += string.Format(" -r {0}:{1}", rev - 1, rev);
        }
        else
        {
            revisions += " -r " + r.Replace("-", ":");
        }
    }

    // pourcentage de complétion pour chaque étape
    int stepPourcent = (int)Math.Floor((double)(100 / (3 + Directory.GetDirectories(cheminRacine + "branches").Length)));

    // merge sur le trunk
    while (bgwkSVN.IsBusy) { }
    bgwkSVN.RunWorkerAsync(new svnCommand(string.Format("merge --accept postpone {0} {1}{2} .", revisions, svnbasepath, branchToMerge), cheminRacine + "trunk", stepPourcent));


    // merge sur chaque branche
    string[] branches = Directory.GetDirectories(cheminRacine + "branches");
    foreach (string b in branches)
    {
        while (bgwkSVN.IsBusy) { }
        bgwkSVN.RunWorkerAsync(new svnCommand(string.Format("merge --accept postpone {0} {1}{2} .", revisions, svnbasepath, branchToMerge), b, stepPourcent));
    }

    // virer les mergeinfo
    while (bgwkSVN.IsBusy) { }
    bgwkSVN.RunWorkerAsync(new svnCommand("pd svn:mergeinfo . -R", cheminRacine, stepPourcent));

    // svn update
    while (bgwkSVN.IsBusy) { }
    bgwkSVN.RunWorkerAsync(new svnCommand("update", cheminRacine, stepPourcent));

    textBoxOutput.Text += Environment.NewLine + "Terminé.";
    MessageBox.Show("Merge terminé.", "Merge terminé", MessageBoxButtons.OK);

    // réactiver les champs et boutons
    activerControles(true);
}

/// <summary>
/// Set up the BackgroundWorker object by attaching event handlers
/// </summary>
private void InitializeBackgroundWorker()
{
    bgwkSVN = new BackgroundWorker();
    bgwkSVN.WorkerReportsProgress = true;
    bgwkSVN.WorkerSupportsCancellation = true;
    bgwkSVN.DoWork += new DoWorkEventHandler(backgroundWorker1_DoWork);
    bgwkSVN.RunWorkerCompleted += new RunWorkerCompletedEventHandler(backgroundWorker1_RunWorkerCompleted);
    bgwkSVN.ProgressChanged += new ProgressChangedEventHandler(backgroundWorker1_ProgressChanged);
}

/// <summary>
/// Exécuter une commande SVN
/// </summary>
private string SVNcmd(svnCommand s, BackgroundWorker worker, DoWorkEventArgs e)
{
    string o = "";
    o += s.path + Environment.NewLine + s.args + Environment.NewLine;

    if (worker.CancellationPending)
    {
        e.Cancel = true;
    }
    else
    {
        Process p = new Process();
        p.StartInfo.WorkingDirectory = s.path;
        p.StartInfo.FileName = "svn";
        p.StartInfo.Arguments = s.args;
        p.StartInfo.CreateNoWindow = true;
        p.StartInfo.RedirectStandardOutput = true;
        p.StartInfo.UseShellExecute = false;
        p.Start();
        o += p.StandardOutput.ReadToEnd() + Environment.NewLine;
        p.WaitForExit();

        if (s.pourcent > 0)
        {
            worker.ReportProgress(s.pourcent);
        }
    }
    return o;
}


/// <summary>
/// Where the actual, potentially time-consuming work is done.
/// </summary>
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    // Get the BackgroundWorker that raised this event.
    BackgroundWorker worker = sender as BackgroundWorker;

    // Assign the result of the computation to the Result property of the DoWorkEventArgs
    // object. This is will be available to the RunWorkerCompleted eventhandler.
    e.Result = SVNcmd((svnCommand)e.Argument, worker, e);
}

/// <summary>
/// Deals with the results of the background operation
/// </summary>
private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    // First, handle the case where an exception was thrown.
    if (e.Error != null)
    {
        MessageBox.Show(e.Error.Message);
    }
    else if (e.Cancelled)
    {
        textBoxOutput.Text += Environment.NewLine + "Annulé.";
    }
    else
    {
        textBoxOutput.Text += e.Result.ToString();
    }
}

/// <summary>
/// Updates the progress bar
/// </summary>
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    this.progressBarTraitement.Value += e.ProgressPercentage;
}

Thanks !

Answer 1

The solution is simple: have one BGW execute all of the commands, not just one BGW for each command. You'll need a List<svnCommand> to store the commands so you can easily pass them to RunWorkerAsync(). DoWork() can simply iterate the list with foreach.