What I need to do is be able to cancel a task that is running async.
I have been searching and cannot seem to wrap my head around it. I just cant seem to discern how it would be implemented into my current setup.
Here is my code that fires my task off. Any help on where or how to implement a cancellation token would be greatly appreciated.
private async void startThread()
{
//do ui stuff before starting
ProgressLabel.Text = String.Format("0 / {0} Runs Completed", index.Count());
ProgressBar.Maximum = index.Count();
await ExecuteProcesses();
//sort list of output lines
outputList = outputList.OrderBy(o => o.RunNumber).ToList();
foreach (Output o in outputList)
{
string outStr = o.RunNumber + "," + o.Index;
foreach (double oV in o.Values)
{
outStr += String.Format(",{0}", oV);
}
outputStrings.Add(outStr);
}
string[] csvOut = outputStrings.ToArray();
File.WriteAllLines(settings.OutputFile, csvOut);
//do ui stuff after completing.
ProgressLabel.Text = index.Count() + " runs completed. Output written to file test.csv";
}
private async Task ExecuteProcesses()
{
await Task.Factory.StartNew(() =>
{
int myCount = 0;
int maxRuns = index.Count();
List<string> myStrings = index;
Parallel.ForEach(myStrings,
new ParallelOptions()
{
MaxDegreeOfParallelism = settings.ConcurrentRuns
}, (s) =>
{
//This line gives us our run count.
int myIndex = myStrings.IndexOf(s) + 1;
string newInputFile = Path.Combine(settings.ProjectPath + "files/", Path.GetFileNameWithoutExtension(settings.InputFile) + "." + s + ".inp");
string newRptFile = Path.Combine(settings.ProjectPath + "files/", Path.GetFileNameWithoutExtension(settings.InputFile) + "." + s + ".rpt");
try
{
//load in contents of input file
string[] allLines = File.ReadAllLines(Path.Combine(settings.ProjectPath, settings.InputFile));
string[] indexSplit = s.Split('.');
//change parameters here
int count = 0;
foreach (OptiFile oF in Files)
{
int i = Int32.Parse(indexSplit[count]);
foreach (OptiParam oP in oF.Parameters)
{
string line = allLines[oP.LineNum - 1];
if (oP.DecimalPts == 0)
{
string sExpression = oP.Value;
sExpression = sExpression.Replace("%i", i.ToString());
EqCompiler oCompiler = new EqCompiler(sExpression, true);
oCompiler.Compile();
int iValue = (int)oCompiler.Calculate();
allLines[oP.LineNum - 1] = line.Substring(0, oP.ColumnNum - 1) + iValue.ToString() + line.Substring(oP.ColumnNum + oP.Length);
}
else
{
string sExpression = oP.Value;
sExpression = sExpression.Replace("%i", i.ToString());
EqCompiler oCompiler = new EqCompiler(sExpression, true);
oCompiler.Compile();
double dValue = oCompiler.Calculate();
dValue = Math.Round(dValue, oP.DecimalPts);
allLines[oP.LineNum - 1] = line.Substring(0, oP.ColumnNum - 1) + dValue.ToString() + line.Substring(oP.ColumnNum + oP.Length);
}
}
count++;
}
//write new input file here
File.WriteAllLines(newInputFile, allLines);
}
catch (IOException ex)
{
MessageBox.Show(ex.ToString());
}
var process = new Process();
process.StartInfo = new ProcessStartInfo("swmm5.exe", newInputFile + " " + newRptFile);
process.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;
process.Start();
process.WaitForExit();
Output output = new Output();
output.RunNumber = myIndex;
output.Index = s;
output.Values = new List<double>();
foreach(OutputValue oV in OutputValues) {
output.Values.Add(oV.getValue(newRptFile));
}
outputList.Add(output);
//get rid of files after run
File.Delete(newInputFile);
File.Delete(newRptFile);
myCount++;
ProgressBar.BeginInvoke(
new Action(() =>
{
ProgressBar.Value = myCount;
}
));
ProgressLabel.BeginInvoke(
new Action(() =>
{
ProgressLabel.Text = String.Format("{0} / {1} Runs Completed", myCount, maxRuns);
}
));
});
});
}
You can cancel an asynchronous operation after a period of time by using the CancellationTokenSource. CancelAfter method if you don't want to wait for the operation to finish.
A CancellationToken enables cooperative cancellation between threads, thread pool work items, or Task objects. You create a cancellation token by instantiating a CancellationTokenSource object, which manages cancellation tokens retrieved from its CancellationTokenSource.
Async methods are intended to be non-blocking operations. An await expression in an async method doesn't block the current thread while the awaited task is running. Instead, the expression signs up the rest of the method as a continuation and returns control to the caller of the async method.
StartNew() . Inside the task, there is a while loop that performs processing as long as the task hasn't been canceled. From my understanding, if cancellationToken. IsCancellationRequested is ever true, the else within my while loop will run and the task will stop.
The best way to support cancellation is to pass a CancellationToken
to the async
method. The button press can then be tied to cancelling the token
class TheClass
{
CancellationTokenSource m_source;
void StartThread() {
m_source = new CancellationTokenSource;
StartThread(m_source.Token);
}
private async void StartThread(CancellationToken token) {
...
}
private void OnCancelClicked(object sender, EventArgs e) {
m_source.Cancel();
}
}
This isn't quite enough though. Both the startThread
and StartProcess
methods will need to be updated to cooperatively cancel the task once the CancellationToken
registers as cancelled
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