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Communicate with process in C#

I need to communicate with external executable (ampl.exe) using standard input and standard output. This exe make calculations during some minutes with some display in the console. It has a prompt so I can succesively launch calculations by using its standard input as soon as a calculation is finished.
The external exe is launched as :
var myProcess = new Process();
myProcess.StartInfo = new ProcessStartInfo("ampl.exe");
myProcess.StartInfo.CreateNoWindow = true;
myProcess.StartInfo.UseShellExecute = false;
myProcess.StartInfo.RedirectStandardOutput = true;
myProcess.StartInfo.RedirectStandardError = true;
myProcess.StartInfo.RedirectStandardInput = true;
myProcess.Start();
I communicate with it by using myProcess.StandardInput and myProcess.StandardOutput (synchronous way).
I use standard input to launch the calcul, for example :
myProcess.StandardInput.WriteLine("solve;");
I want to wait the end of the solve statement, get results in files, prepare new calculation input files and then launching a second solve.
My problem is that I do now know when the first calculation is finished, that is when the exe is waiting for new command in its standard input.
The only way I found is to add a specific display command and wait for getting it it its standard output :
myProcess.StandardInput.WriteLine("solve;");
myProcess.StandardInput.WriteLine("print 'calculDone';");
string output = myProcess.StandardOutput.ReadLine();
while (!output.Contains("calculDone"))
{
output = myProcess.StandardOutput.ReadLine();
}
Is there another way avoiding to use this display command to do this ?
Edit : following advices, I tried the asynchronous way. But I still need to print 'CalculDone' to know when the solve statement ended. I do not get the prompt of ampl.exe (which is 'ampl : ') in the standard output of the process.
AutoResetEvent eventEnd = new AutoResetEvent(false);
var myProcess = new Process();
myProcess.StartInfo = new ProcessStartInfo("ampl.exe");
myProcess.StartInfo.CreateNoWindow = true;
myProcess.StartInfo.UseShellExecute = false;
myProcess.StartInfo.RedirectStandardOutput = true;
myProcess.StartInfo.RedirectStandardError = true;
myProcess.StartInfo.RedirectStandardInput = true;
myProcess.EnableRaisingEvents = true;
myProcess.OutputDataReceived += (sender, e) =>
{
if (e.Data == "commandDone")
{
eventEnd.Set();
}
else if (e.Data != null)
{
Console.WriteLine("ampl: {0}", e.Data);
}
};
myProcess.Start();
myProcess.BeginOutputReadLine();
myProcess.StandardInput.WriteLine("solve;");
myProcess.StandardInput.WriteLine("print 'commandDone';");
eventEnd.WaitOne();

The best option would be to use the Processs.OutputDataReceived event instead of a tight while loop. It’s like the event async pattern, you launch an asynchronous task and wait for an event callback telling you it’s done. The continuation of the asynchronous task would go in the event handler. Remember to unsubscribe the event handler the first time it goes off, otherwise it will be firing when you don’t want it to.
Another option I have never tried is Process.WaitForInputIdle() method, but I’m not sure if this will work in your particular case. If it does you wouldn’t need to write anything to the input stream.

Start an offline ClickOnce Application and wait for Exit

I have deployed a ClickOnce Windows Forms application (App A)
Another application (App B) starts App A with a filename as parameter.
I do this with this Code
var basePath = Environment.GetFolderPath(Environment.SpecialFolder.Programs);
var location = String.Format(#"{0}\{1}\{2}\{3}",
basePath, "MyCompany", "MyProduct", "MyApp.appref-ms");
var fileName = #"c:\temp\somefile.ext";
var uri = new Uri(fileName).ToString();
Process.Start(location, uri);
App A grabs the file name from AppDomain.CurrentDomain.SetupInformation.ActivationArguments.ActivationData[0] and show the content.
This works like a charm. However, now I want App B to wait for App A to exit.
But a call to Process.WaitForExit() returns instantly.
Is there a way to open a ClickOnce App and wait for it to exit? I can, if necessary, change the way the app is opend but the requirement is that I need to run the app as a ClickOnce app (I know that somewhere in my user profile AppData\Local\Apps\2.0\ folder the exe exists and can be started directly but If I do that ApplicationDeployment.IsNetworkDeployed is false and ApplicationDeployment.CurrentDeployment is null. In that I loose the ClickOnce Update Capabilities).

my suggestion would be to use Mutex in App A, and let App B check and wait for it. This is the cleanest way from my point of view.
App A does this when starts:
private static Mutex mutex;
public static void Main()
{
// if you want your app to be limited to a single instance
// across ALL SESSIONS (multiple users & terminal services), then use the following line instead:
// string mutexName = string.Format("Global\\{0}", ProgramInfo.AssemblyGuid);
var mutexName = string.Format("Local\\{0}", SOME_SHARED_GUID);
mutex = new Mutex(true, mutexName, out singleInstance);
if (singleInstance == false)
{
// that means your app has more than one instance running
// you need to decide what to do here.
}
// rest of initialization code
Application.Run();
// release the mutex so App B can continue
mutex.ReleaseMutex();
}
and App B just waits for the mutex to be released:
Process.Start(location, uri);
Thread.Sleep(5000); // give it 5 seconds or so to check for updates and start
var mutexName = string.Format("Local\\{0}", SOME_SHARED_GUID);
mutex = new Mutex(false, mutexName);
mutex.WaitOne();

The problem is that starting the appref-ms process does not actually start the application it starts the deployment manifest, which then launches the application itself, so the process you are starting exits straight away.
You can add a check to see when you application has started if you know the name (which I assume you do) like this:
string myAppName = "YourAppName";
DateTime startTime = DateTime.Now;
int newProcessId = 0;
List<int> runningProcessIds = new List<int>();
//find all the running processes and record their Ids
foreach (void proc_loopVariable in Process.GetProcessesByName(myAppName)) {
proc = proc_loopVariable;
runningProcessIds.Add(proc.Id);
}
//start the new process
Process.Start(location);
//wait for the new application to be started
while (!(Process.GetProcessesByName(myAppName).Count != runningProcessIds.Count)) {
//timeout if we have not seen the application start
if ((DateTime.Now - startTime).TotalSeconds > 30)
break;
}
//loop through all the running processes again to find the id of the one that has just started
foreach (void proc_loopVariable in Process.GetProcessesByName(myAppName)) {
proc = proc_loopVariable;
if (!runningProcessIds.Contains(proc.Id)) {
newProcessId = proc.Id;
break;
}
}
//wait for the application to finish
Process.GetProcessById(newProcessId).WaitForExit();
Debug.WriteLine("Finished");

Invoke UI application in a thread

I've 2 exe (A, B) and one dll (C).
A is an exe that user invokes from commandline with argument -ui or -file_path.
if -ui is passed: B is used to show UI.
if -file_path is passed, C is used for further functionality.
if -ui is passed, i use following code (in Main method):
System.Threading.Thread a = new System.Threading.Thread(yah);
a.Start();
static void yah()
{
SyngoViaInstallerUI.Program.Main();
}
but it blocks the command line from where exe A was invoked. is it possible to unblock the cmdLine or i should to create a new process for -ui argument?
Thanks.

you have to create seperate process for B in order to release the process A and finish gracefully.

Following code works, but is this correct way?
System.Diagnostics.Process pr = new System.Diagnostics.Process();
System.Diagnostics.ProcessStartInfo psi = new System.Diagnostics.ProcessStartInfo();
psi.FileName = #"file_path";
pr.StartInfo = psi;
pr.Start();
Thanks.

Process.Start vs Process `p = new Process()` in C#?

As is asked in this post, there are two ways to call another process in C#.
Process.Start("hello");
And
Process p = new Process();
p.StartInfo.FileName = "hello.exe";
p.Start();
p.WaitForExit();
Q1 : What are the pros/cons of each approach?
Q2 : How to check if error happens with the Process.Start() method?

With the first method you might not be able to use WaitForExit, as the method returns null if the process is already running.
How you check if a new process was started differs between the methods. The first one returns a Process object or null:
Process p = Process.Start("hello");
if (p != null) {
// A new process was started
// Here it's possible to wait for it to end:
p.WaitForExit();
} else {
// The process was already running
}
The second one returns a bool:
Process p = new Process();
p.StartInfo.FileName = "hello.exe";
bool s = p.Start();
if (s) {
// A new process was started
} else {
// The process was already running
}
p.WaitForExit();

For simple cases, the advantage is mainly convenience. Obviously you have more options (working path, choosing between shell-exec, etc) with the ProcessStartInfo route, but there is also a Process.Start(ProcessStartInfo) static method.
Re checking for errors; Process.Start returns the Process object, so you can wait for exit and check the error code if you need. If you want to capture stderr, you probably want either of the ProcessStartInfo approaches.

Very little difference. The static method returns a process object, so you can still use the "p.WaitForExit()" etc - using the method where you create a new process it would be easier to modify the process parameters (processor affinity and such) before launching the process.
Other than that - no difference. A new process object is created both ways.
In your second example - that is identical to this:
Process p = Process.Start("hello.exe");
p.WaitForExit();

Hanging process when run with .NET Process.Start -- what's wrong?

I wrote a quick and dirty wrapper around svn.exe to retrieve some content and do something with it, but for certain inputs it occasionally and reproducibly hangs and won't finish. For example, one call is to svn list:
svn list "http://myserver:84/svn/Documents/Instruments/" --xml --no-auth-cache --username myuser --password mypassword
This command line runs fine when I just do it from a command shell, but it hangs in my app. My c# code to run this is:
string cmd = "svn.exe";
string arguments = "list \"http://myserver:84/svn/Documents/Instruments/\" --xml --no-auth-cache --username myuser --password mypassword";
int ms = 5000;
ProcessStartInfo psi = new ProcessStartInfo(cmd);
psi.Arguments = arguments;
psi.RedirectStandardOutput = true;
psi.WindowStyle = ProcessWindowStyle.Normal;
psi.UseShellExecute = false;
Process proc = Process.Start(psi);
StreamReader output = new StreamReader(proc.StandardOutput.BaseStream, Encoding.UTF8);
proc.WaitForExit(ms);
if (proc.HasExited)
{
return output.ReadToEnd();
}
This takes the full 5000 ms and never finishes. Extending the time doesn't help. In a separate command prompt, it runs instantly, so I'm pretty sure it's unrelated to an insufficient waiting time. For other inputs, however, this seems to work fine.
I also tried running a separate cmd.exe here (where exe is svn.exe and args is the original arg string), but the hang still occurred:
string cmd = "cmd";
string arguments = "/S /C \"" + exe + " " + args + "\"";
What could I be screwing up here, and how can I debug this external process stuff?
EDIT:
I'm just now getting around to addressing this. Mucho thanks to Jon Skeet for his suggestion, which indeed works great. I have another question about my method of handling this, though, since I'm a multi-threaded novice. I'd like suggestions on improving any glaring deficiencies or anything otherwise dumb. I ended up creating a small class that contains the stdout stream, a StringBuilder to hold the output, and a flag to tell when it's finished. Then I used ThreadPool.QueueUserWorkItem and passed in an instance of my class:
ProcessBufferHandler bufferHandler = new ProcessBufferHandler(proc.StandardOutput.BaseStream,
Encoding.UTF8);
ThreadPool.QueueUserWorkItem(ProcessStream, bufferHandler);
proc.WaitForExit(ms);
if (proc.HasExited)
{
bufferHandler.Stop();
return bufferHandler.ReadToEnd();
}
... and ...
private class ProcessBufferHandler
{
public Stream stream;
public StringBuilder sb;
public Encoding encoding;
public State state;
public enum State
{
Running,
Stopped
}
public ProcessBufferHandler(Stream stream, Encoding encoding)
{
this.stream = stream;
this.sb = new StringBuilder();
this.encoding = encoding;
state = State.Running;
}
public void ProcessBuffer()
{
sb.Append(new StreamReader(stream, encoding).ReadToEnd());
}
public string ReadToEnd()
{
return sb.ToString();
}
public void Stop()
{
state = State.Stopped;
}
}
This seems to work, but I'm doubtful that this is the best way. Is this reasonable? And what can I do to improve it?

One standard issue: the process could be waiting for you to read its output. Create a separate thread to read from its standard output while you're waiting for it to exit. It's a bit of a pain, but that may well be the problem.

Jon Skeet is right on the money!
If you don't mind polling after you launch your svn command try this:
Process command = new Process();
command.EnableRaisingEvents = false;
command.StartInfo.FileName = "svn.exe";
command.StartInfo.Arguments = "your svn arguments here";
command.StartInfo.UseShellExecute = false;
command.StartInfo.RedirectStandardOutput = true;
command.Start();
while (!command.StandardOutput.EndOfStream)
{
Console.WriteLine(command.StandardOutput.ReadLine());
}

I had to drop an exe on a client's machine and use Process.Start to launch it.
The calling application would hang - the issue ended up being their machine assuming the exe was dangerous and preventing other applications from starting it.
Right click the exe and go to properties. Hit "Unblock" toward the bottom next to the security warning.

Based on Jon Skeet's answer this is how I do it in modern day (2021) .NET 5
var process = Process.Start(processStartInfo);
var stdErr = process.StandardError;
var stdOut = process.StandardOutput;
var resultAwaiter = stdOut.ReadToEndAsync();
var errResultAwaiter = stdErr.ReadToEndAsync();
await process.WaitForExitAsync();
await Task.WhenAll(resultAwaiter, errResultAwaiter);
var result = resultAwaiter.Result;
var errResult = errResultAwaiter.Result;
Note that you can't await the standard output before the error, because the wait will hang in case the standard error buffer gets full first (same for trying it the other way around).
The only way is to start reading them asynchronously, wait for the process to exit, and then complete the await by using Task.WaitAll

I know this is an old post but maybe this will assist someone. I used this to execute some AWS (Amazon Web Services) CLI commands using .Net TPL tasks.
I did something like this in my command execution which is executed within a .Net TPL Task which is created within my WinForm background worker bgwRun_DoWork method which holding a loop with while(!bgwRun.CancellationPending). This contains the reading of the Standard Output from the Process via a new Thread using the .Net ThreadPool class.
private void bgwRun_DoWork(object sender, DoWorkEventArgs e)
{
while (!bgwRun.CancellationPending)
{
//build TPL Tasks
var tasks = new List<Task>();
//work to add tasks here
tasks.Add(new Task(()=>{
//build .Net ProcessInfo, Process and start Process here
ThreadPool.QueueUserWorkItem(state =>
{
while (!process.StandardOutput.EndOfStream)
{
var output = process.StandardOutput.ReadLine();
if (!string.IsNullOrEmpty(output))
{
bgwRun_ProgressChanged(this, new ProgressChangedEventArgs(0, new ExecutionInfo
{
Type = "ExecutionInfo",
Text = output,
Configuration = s3SyncConfiguration
}));
}
if (cancellationToken.GetValueOrDefault().IsCancellationRequested)
{
break;
}
}
});
});//work Task
//loop through and start tasks here and handle completed tasks
} //end while
}

I know my SVN repos can run slow sometimes, so maybe 5 seconds isn't long enough? Have you copied the string you are passing to the process from a break point so you are positive it's not prompting you for anything?