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Forcing timeout on a process in .NET 6

I come from a C background, and my knowledge of C# and .NET is very very limited.
Now, I am running an executable in my code as a Process, in a .NET 6.0 application. This is what the code looks like
static string ExternalExe(string input)
{
string output = string.Empty;
ProcessStartInfo info = new()
{
FileName = "path_here",
Arguments = input,
RedirectStandardOutput = true,
UseShellExecute = false
};
using (Process? process = Process.Start(info))
{
if (process != null)
{
output = process.StandardOutput.ReadToEnd();
process.WaitForExit();
}
else
{
throw new CustomException();
}
}
return output;
}
I want to implement a timeout for this. As in, if the process takes, for example, more than 1 second to exit, it should generate an exception or something like that. How would I implement that?
Any help would be much appreciated, and thanks in advance. :)

You could use the WaitForExit(TimeSpan) but this will block your UI thread. Since we're in .NET6 I would use the asynchronous version with a CancellationTokenSource set to automatically cancel after x ms.
await process.WaitForExitAsync(new CancellationTokenSource(3000).Token);

Why does calling the Tesseract process cause this service to crash randomly?

I have a .NET Core 2.1 service which runs on an Ubuntu 18.04 VM and calls Tesseract OCR 4.00 via a Process instance. I would like to use an API wrapper, but I could only find one available and it is only in beta for the latest version of Tesseract -- the stable wrapper uses version 3 instead of 4. In the past, this service worked well enough, but I have been changing it so that document/image data is written and read from disk less frequently in an attempt to improve speed. The service used to call many more external processes (such as ImageMagick) which were unnecessary due to the presence of an API, so I have been replacing those with API calls.
Recently I've been testing this with a sample file taken from real data. It's a faxed document PDF that has 133 pages, but is only 5.8 MB in spite of that due to grayscale and resolution. The service takes a document, splits it into individual pages, then assigns multiple threads (one thread per page) to call Tesseract and process them using Parallel.For. The thread limits are configurable. I am aware that Tesseract has its own multithreading environment variable (OMP_THREAD_LIMIT). I found in prior testing that setting it to "1" is ideal for our set up at the moment, but in my recent testing for this issue I have tried leaving it unset (dynamic value) with no improvement.
The issue is that unpredictably, when Tesseract is called, the service will hang for about a minute and then crash, with the only error showing in journalctl being:
dotnet[32328]: Error while reaping child. errno = 10
dotnet[32328]: at System.Environment.FailFast(System.String, System.Exception)
dotnet[32328]: at System.Environment.FailFast(System.String)
dotnet[32328]: at System.Diagnostics.ProcessWaitState.TryReapChild()
dotnet[32328]: at System.Diagnostics.ProcessWaitState.CheckChildren(Boolean)
dotnet[32328]: at System.Diagnostics.Process.OnSigChild(Boolean)
I can't find anything at all online for this particular error. It would seem to me, based on related research I've done on the Process class, that this is occurring when the process is exiting and dotnet is trying to clean up the resources it was using. I'm really at a loss as to how to even approach this problem, although I have tried a number of "guesses" such as changing thread limit values. There is no cross-over between threads. Each thread has its own partition of pages (based on how Parallel.For partitions a collection) and it sets to work on those pages, one at a time.
Here is the process call, called from within multiple threads (8 is the limit we normally set):
private bool ProcessOcrPage(IMagickImage page, int pageNumber, object instanceId)
{
var inputPageImagePath = Path.Combine(_fileOps.GetThreadWorkingDirectory(instanceId), $"ocrIn_{pageNumber}.{page.Format.ToString().ToLower()}");
string outputPageFilePathWithoutExt = Path.Combine(_fileOps.GetThreadOutputDirectory(instanceId),
$"pg_{pageNumber.ToString().PadLeft(3, '0')}");
page.Write(inputPageImagePath);
var cmdArgs = $"-l eng \"{inputPageImagePath}\" \"{outputPageFilePathWithoutExt}\" pdf";
bool success;
_logger.LogStatement($"[Thread {instanceId}] Executing the following command:{Environment.NewLine}tesseract {cmdArgs}", LogLevel.Debug);
var psi = new ProcessStartInfo("tesseract", cmdArgs)
{
RedirectStandardError = true,
RedirectStandardOutput = true,
UseShellExecute = false,
CreateNoWindow = true
};
// 0 is not the default value for this environment variable. It should remain unset if there
// is no config value, as it is determined dynamically by default within OpenMP.
if (_processorConfig.TesseractThreadLimit > 0)
psi.EnvironmentVariables.Add("OMP_THREAD_LIMIT", _processorConfig.TesseractThreadLimit.ToString());
using (var p = new Process() { StartInfo = psi })
{
string standardErr, standardOut;
int exitCode;
p.Start();
standardOut = p.StandardOutput.ReadToEnd();
standardErr = p.StandardError.ReadToEnd();
p.WaitForExit();
exitCode = p.ExitCode;
if (!string.IsNullOrEmpty(standardOut))
_logger.LogStatement($"Tesseract stdOut:\n{standardOut}", LogLevel.Debug, nameof(ProcessOcrPage));
if (!string.IsNullOrEmpty(standardErr))
_logger.LogStatement($"Tesseract stdErr:\n{standardErr}", LogLevel.Debug, nameof(ProcessOcrPage));
success = p.ExitCode == 0;
}
return success;
}
EDIT 4: After much testing and discussion with Clint in chat, here is what we learned. The error is raised from a Process event "OnSigChild," that much is obvious from the stack trace, but there is no way to hook into the same event that raises this error. The process never times out given a timeout of 10 seconds (Tesseract typically only takes a few seconds to process a given page). Curiously, if the process timeout is removed and I wait on the standard output and error streams to close, it will hang for a good 20-30 seconds, but the process does not appear in ps auxf during this hang time. From the best that I can tell, Linux is able to determine that the process is done executing, but .NET is not. Otherwise, the error seems to be raised at the very moment that the process is done executing.
The most baffling thing to me is still that the process handling part of the code really hasn't changed very much compared to the working version of this code we have in production. This suggests that it's an error I made somewhere, but I am simply unable to find it. I think I will have to open up an issue on the dotnet GitHub tracker.

"Error while reaping child"
Processes hold up some resources in the kernel, On Unix, when the parent dies, it is the init process that is responsible for cleaning up the kernel resources both Zombine and Orphan process (aka reaping the child). .NET Core reaps child processes as soon as they terminate.
"I have discovered that removing the stdout and stderr stream ReadToEnd
calls causes the processes to end immediately instead of hang, with
the same error"
The error is due to the fact that you are prematurely calling p.ExitCode even before the process has finished and with the ReadToEnd you are just delaying this activity
Summary of updated code
StartInfo.FileName should point to a filename that you want to start
UseShellExecute to false if the process should be created directly from the executable file and true if you intend that shell should be used when starting the process;
Added asynchrnous read operations to standard ouput and error streams
AutoResetEvents to signal when the output and error when the operations complete
Process.Close() to release the resources
It is easier to set and use ArgumentList over Arguments property
Redhat Blog on NetProcess on Linux
Revised Module
private bool ProcessOcrPage(IMagickImage page, int pageNumber, object instanceId)
{
StringBuilder output = new StringBuilder();
StringBuilder error = new StringBuilder();
int exitCode;
var inputPageImagePath = Path.Combine(_fileOps.GetThreadWorkingDirectory(instanceId), $"ocrIn_{pageNumber}.{page.Format.ToString().ToLower()}");
string outputPageFilePathWithoutExt = Path.Combine(_fileOps.GetThreadOutputDirectory(instanceId),
$"pg_{pageNumber.ToString().PadLeft(3, '0')}");
page.Write(inputPageImagePath);
var cmdArgs = $"-l eng \"{inputPageImagePath}\" \"{outputPageFilePathWithoutExt}\" pdf";
bool success;
_logger.LogStatement($"[Thread {instanceId}] Executing the following command:{Environment.NewLine}tesseract {cmdArgs}", LogLevel.Debug);
using (var outputWaitHandle = new AutoResetEvent(false))
using (var errorWaitHandle = new AutoResetEvent(false))
{
try
{
using (var process = new Process())
{
process.StartInfo = new ProcessStartInfo
{
WindowStyle = ProcessWindowStyle.Hidden,
FileName = "tesseract.exe", // Verify if this is indeed the process that you want to start ?
RedirectStandardOutput = true,
RedirectStandardError = true,
UseShellExecute = false,
CreateNoWindow = true,
Arguments = cmdArgs,
WorkingDirectory = Path.GetDirectoryName(path)
};
if (_processorConfig.TesseractThreadLimit > 0)
process.StartInfo.EnvironmentVariables.Add("OMP_THREAD_LIMIT", _processorConfig.TesseractThreadLimit.ToString());
process.OutputDataReceived += (sender, e) =>
{
if (e.Data == null)
{
outputWaitHandle.Set();
}
else
{
output.AppendLine(e.Data);
}
};
process.ErrorDataReceived += (sender, e) =>
{
if (e.Data == null)
{
errorWaitHandle.Set();
}
else
{
error.AppendLine(e.Data);
}
};
process.Start();
process.BeginOutputReadLine();
process.BeginErrorReadLine();
if (!outputWaitHandle.WaitOne(ProcessTimeOutMiliseconds) && !errorWaitHandle.WaitOne(ProcessTimeOutMiliseconds) && !process.WaitForExit(ProcessTimeOutMiliseconds))
{
//To cancel the read operation if the process is stil reading after the timeout this will prevent ObjectDisposeException
process.CancelOutputRead();
process.CancelErrorRead();
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Timed Out");
//To release allocated resource for the Process
process.Close();
//Timed out
return false;
}
Console.ForegroundColor = ConsoleColor.Green;
Console.WriteLine("Completed On Time");
exitCode = process.ExitCode;
if (!string.IsNullOrEmpty(standardOut))
_logger.LogStatement($"Tesseract stdOut:\n{standardOut}", LogLevel.Debug, nameof(ProcessOcrPage));
if (!string.IsNullOrEmpty(standardErr))
_logger.LogStatement($"Tesseract stdErr:\n{standardErr}", LogLevel.Debug, nameof(ProcessOcrPage));
process.Close();
return exitCode == 0 ? true : false;
}
}
Catch
{
//Handle Exception
}
}
}

Execute a few commands via C# console-app

I'm new to C# (and development in general). I need to write a method in C# that will execute following via console:
- install Newman;
- execute postman Run.
I've created a method as below (I tried 2 options: ReadToEnd and WaitForExit), but it seems to stuck at each of these steps.
Any help how to make this to execute both commands in sequence (1st needs to finish before 2nd start) and exit after 2nd command executed fully?
Thanks in advance.
public string Runner ()
{
string readOutput = null;
var psiNpm = new ProcessStartInfo
{
FileName = "cmd",
RedirectStandardOutput = true,
RedirectStandardInput = true,
UseShellExecute = false
};
var pNpmRun = Process.Start(psiNpm);
pNpmRun.StandardInput.WriteLine($"npm install -g newman");
pNpmRun.WaitForExit();
//pNpmRun.StandardOutput.ReadToEnd();
pNpmRun.StandardInput.WriteLine($"newman run " +
$"\"C:\\Postman\\Test.postman.json\" " +
$"--folder \"TestSearch\" " +
$"--environment \"C:\\Postman\\postman_environment.json\" " +
$"--disable-unicode");
pNpmRun.StandardOutput.ReadToEnd();
pNpmRun.WaitForExit();
return readOutput = pNpmRun.StandardOutput.ReadLine();
}

Try writing an exit command to your cmd input stream.
The issue, is the commands you sent (npm, newman) are executing, then control is returning to the shell (cmd), which is then waiting for more user input to be sent. You need to tell it to quit by sending "exit". You should only have 1 WaitForExit call. The WaitForExit is waiting for the cmd process to exit, not the individual commands you send to it.
Next, you should move ReadToEnd after the process has exited (after WaitForExit). Here is a question concering why: ReadToEnd from std output of process and waitforexit
So, something like this:
public string Runner ()
{
var psiNpm = new ProcessStartInfo
{
FileName = "cmd",
RedirectStandardOutput = true,
RedirectStandardInput = true,
UseShellExecute = false
};
var pNpmRun = Process.Start(psiNpm);
pNpmRun.StandardInput.WriteLine("npm install -g newman");
pNpmRun.StandardInput.WriteLine("newman run " +
"\"C:\\Postman\\Test.postman.json\" " +
"--folder \"TestSearch\" " +
"--environment \"C:\\Postman\\postman_environment.json\" " +
"--disable-unicode");
pNpmRun.StandardInput.WriteLine("exit");
pNpmRun.WaitForExit();
return pNpmRun.StandardOutput.ReadToEnd();
You might also consider adding a timeout to the WaitForExit. If these cmds get stuck for some reason your calling process is also going to get stuck waiting for them to complete. Usually best to eventually fail than have a bunch of hung processes. You could then kill the process if the timeout expires.
var tenMin = 10 * 60 * 1000;
if(pNpmRun.WaitForExit(tenMin)) {
return pNpmRun.StandardOutput.ReadToEnd();
} else {
pNpmRun.Kill();
throw new TimeoutException("Command didn't complete in 10 minute timeout");
}

Queuing installations via Process.Start

I need to queue approximately 20 installations that are fully unattended (Using a C# winform application). Each installation has its own INI file (that is manually created) that contains the proper information on what arguments each installer requires for this procedure (read in before that program is executed). I'm running into issues with many application that when the setup.exe is executed the process closes immediately and launches its MSI (if applicable), causing my procedure to carry out with the next installation assuming that the first is complete. I have read similar problems snooping around the web, but no real solution on the issue... (some workarounds included using a batch file with the /Wait option which should have kept the setup.exe in memory until its MSI has completed). The setup.exe must be launched due to the fact that they contain bootstrappers.
What options do i have to resolve this dilemma?
Here is some sample code that demonstrates the procedure:
foreach (ListViewItem itm in this.lstSoftwares.Items)
{
try
{
if (itm.Checked)
{
lblStatus.Text = "Status: Installing " + current.ToString() + " of " + count.ToString();
string InstallPath = Path.Combine(Application.StartupPath, "Software",
itm.Text, itm.Tag.ToString());
string CommandLine = itm.SubItems[1].Text;
Process process = new Process();
process.StartInfo.FileName = InstallPath;
process.StartInfo.Arguments = CommandLine;
process.StartInfo.WindowStyle = ProcessWindowStyle.Normal;
process.Start();
process.WaitForExit();
this.lstSoftwares.Items[i].SubItems[2].Text = "Complete";
current++;
}
Update
right after waitforexit() i'm using a loop that checks if the msiexec is running:
private bool MSIRunning()
{
try
{
using (var mutex = Mutex.OpenExisting(#"Global\_MSIExecute"))
{
return true;
}
}
catch (Exception)
{
return false;
}
}
this is a hack in my opionion, but doing the trick so far...

Querying the MSI Mutex after process.start in a loop (check if Mutex is running every 3 seconds, if not return and proceed with next install) seemed to solve the problem (Noted above).

Already answered, but I have a slightly more robust implementation of the MSI mutex check:
public bool IsMsiExecFree(TimeSpan maxWaitTime)
{
_logger.Info(#"Waiting up to {0}s for Global\_MSIExecute mutex to become free...", maxWaitTime.TotalSeconds);
// The _MSIExecute mutex is used by the MSI installer service to serialize installations
// and prevent multiple MSI based installations happening at the same time.
// For more info: http://msdn.microsoft.com/en-us/library/aa372909(VS.85).aspx
const string installerServiceMutexName = "Global\\_MSIExecute";
Mutex msiExecuteMutex = null;
var isMsiExecFree = false;
try
{
msiExecuteMutex = Mutex.OpenExisting(installerServiceMutexName,
MutexRights.Synchronize);
isMsiExecFree = msiExecuteMutex.WaitOne(maxWaitTime, false);
}
catch (WaitHandleCannotBeOpenedException)
{
// Mutex doesn't exist, do nothing
isMsiExecFree = true;
}
catch (ObjectDisposedException)
{
// Mutex was disposed between opening it and attempting to wait on it, do nothing
isMsiExecFree = true;
}
finally
{
if (msiExecuteMutex != null && isMsiExecFree)
msiExecuteMutex.ReleaseMutex();
}
_logger.Info(#"Global\_MSIExecute mutex is free, or {0}s has elapsed.", maxWaitTime.TotalSeconds);
return isMsiExecFree;
}

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?