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Stop process using CancellationToken

I need to run different instances of a Worker Service (BackgroundService): same code but different configuration.
The number of instances and the start and stop of every instance will change during the running process.
So my choice was to write 2 programs:
WorkerProgram: the Worker Service
MainProgram: manage (start and stop) of every different instance of WorkerProgram
Sample code of WorkerProgram:
var host = Host.CreateDefaultBuilder()
.ConfigureServices(services =>
{
services.AddSingleton(new Instance { Id = int.Parse(args[0])});
services.AddHostedService<Worker>();
})
.Build();
await host.RunAsync();
public class Worker : BackgroundService
{
private readonly Instance _instance;
public Worker(Instance instance)
{
_instance = instance;
}
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
while (!stoppingToken.IsCancellationRequested)
{
_logger.LogInformation("Running {}", _instance.Id);
await Task.Delay(10000, stoppingToken);
_logger.LogInformation("END");
}
}
}
MainProgram starts every WorkerProgram using
var process = new Process();
process.StartInfo.Filename = "WorkerProgram.exe";
process.StartInfo.Arguments = i.ToString();
process.Start();
so every Worker Service run in a different process.
But when it needs to stop them, the command
process.Kill();
will Kill the process in the middle of run.
How can I stop the process in a better way (eg. using CancellationToken)?
Thank you!
My current (bad) solution is to create a placeholder file for every BackgroundService. And check the existence of the file at every cicle.

untested, but:
cancellationToken.ThrowIfCancellationRequested();
process.Start();
using (cancellationToken.Register(static state => {
try {
(state as Process)?.Close(); // or Kill, or both; your choice
} catch (Exception ex) {
// best efforts only
Debug.WriteLine(ex.Message);
}
}, process))
{
await process.WaitForExitAsync(cancellationToken);
}
The Register here will deal with killing the process in the cancellation case; if the external process exits before then, we will unregister via the using after the WaitForExitAsync, and won't attempt to kill it.

Process sometimes hangs while waiting for Exit

What may be the reason of my process hanging while waiting for exit?
This code has to start powershell script which inside performs many action e.g start recompiling code via MSBuild, but probably the problem is that it generates too much output and this code gets stuck while waiting to exit even after power shell script executed correctly
it's kinda "weird" because sometimes this code works fine and sometimes it just gets stuck.
Code hangs at:
process.WaitForExit(ProcessTimeOutMiliseconds);
Powershell script executes in like 1-2sec meanwhile timeout is 19sec.
public static (bool Success, string Logs) ExecuteScript(string path, int ProcessTimeOutMiliseconds, params string[] args)
{
StringBuilder output = new StringBuilder();
StringBuilder error = new StringBuilder();
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 = "powershell.exe",
RedirectStandardOutput = true,
RedirectStandardError = true,
UseShellExecute = false,
Arguments = $"-ExecutionPolicy Bypass -File \"{path}\"",
WorkingDirectory = Path.GetDirectoryName(path)
};
if (args.Length > 0)
{
var arguments = string.Join(" ", args.Select(x => $"\"{x}\""));
process.StartInfo.Arguments += $" {arguments}";
}
output.AppendLine($"args:'{process.StartInfo.Arguments}'");
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();
process.WaitForExit(ProcessTimeOutMiliseconds);
var logs = output + Environment.NewLine + error;
return process.ExitCode == 0 ? (true, logs) : (false, logs);
}
}
finally
{
outputWaitHandle.WaitOne(ProcessTimeOutMiliseconds);
errorWaitHandle.WaitOne(ProcessTimeOutMiliseconds);
}
}
}
Script:
start-process $args[0] App.csproj -Wait -NoNewWindow
[string]$sourceDirectory = "\bin\Debug\*"
[int]$count = (dir $sourceDirectory | measure).Count;
If ($count -eq 0)
{
exit 1;
}
Else
{
exit 0;
}
where
$args[0] = "C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\MSBuild\Current\Bin\MSBuild.exe"
Edit
To #ingen's solution I added small wrapper which retries to execute hanged up MS Build
public static void ExecuteScriptRx(string path, int processTimeOutMilliseconds, out string logs, out bool success, params string[] args)
{
var current = 0;
int attempts_count = 5;
bool _local_success = false;
string _local_logs = "";
while (attempts_count > 0 && _local_success == false)
{
Console.WriteLine($"Attempt: {++current}");
InternalExecuteScript(path, processTimeOutMilliseconds, out _local_logs, out _local_success, args);
attempts_count--;
}
success = _local_success;
logs = _local_logs;
}
Where InternalExecuteScript is ingen's code

Let's start with a recap of the accepted answer in a related post.
The problem is that if you redirect StandardOutput and/or StandardError the internal buffer can become full. Whatever order you use, there can be a problem:
If you wait for the process to exit before reading StandardOutput the process can block trying to write to it, so the process never ends.
If you read from StandardOutput using ReadToEnd then your process can block if the process never closes StandardOutput (for example if it never terminates, or if it is blocked writing to StandardError).
Even the accepted answer, however, struggles with the order of execution in certain cases.
EDIT: See answers below for how avoid an ObjectDisposedException if the timeout occurs.
It's in these kind of situations, where you want to orchestrate several events, that Rx really shines.
Note the .NET implementation of Rx is available as the System.Reactive NuGet package.
Let's dive in to see how Rx facilitates working with events.
// Subscribe to OutputData
Observable.FromEventPattern<DataReceivedEventArgs>(process, nameof(Process.OutputDataReceived))
.Subscribe(
eventPattern => output.AppendLine(eventPattern.EventArgs.Data),
exception => error.AppendLine(exception.Message)
).DisposeWith(disposables);
FromEventPattern allows us to map distinct occurrences of an event to a unified stream (aka observable). This allows us to handle the events in a pipeline (with LINQ-like semantics). The Subscribe overload used here is provided with an Action<EventPattern<...>> and an Action<Exception>. Whenever the observed event is raised, its sender and args will be wrapped by EventPattern and pushed through the Action<EventPattern<...>>. When an exception is raised in the pipeline, Action<Exception> is used.
One of the drawbacks of the Event pattern, clearly illustrated in this use case (and by all the workarounds in the referenced post), is that it's not apparent when / where to unsubscribe the event handlers.
With Rx we get back an IDisposable when we make a subscription. When we dispose of it, we effectively end the subscription. With the addition of the DisposeWith extension method (borrowed from RxUI), we can add multiple IDisposables to a CompositeDisposable (named disposables in the code samples). When we're all done, we can end all subscriptions with one call to disposables.Dispose().
To be sure, there's nothing we can do with Rx, that we wouldn't be able to do with vanilla .NET. The resulting code is just a lot easier to reason about, once you've adapted to the functional way of thinking.
public static void ExecuteScriptRx(string path, int processTimeOutMilliseconds, out string logs, out bool success, params string[] args)
{
StringBuilder output = new StringBuilder();
StringBuilder error = new StringBuilder();
using (var process = new Process())
using (var disposables = new CompositeDisposable())
{
process.StartInfo = new ProcessStartInfo
{
WindowStyle = ProcessWindowStyle.Hidden,
FileName = "powershell.exe",
RedirectStandardOutput = true,
RedirectStandardError = true,
UseShellExecute = false,
Arguments = $"-ExecutionPolicy Bypass -File \"{path}\"",
WorkingDirectory = Path.GetDirectoryName(path)
};
if (args.Length > 0)
{
var arguments = string.Join(" ", args.Select(x => $"\"{x}\""));
process.StartInfo.Arguments += $" {arguments}";
}
output.AppendLine($"args:'{process.StartInfo.Arguments}'");
// Raise the Process.Exited event when the process terminates.
process.EnableRaisingEvents = true;
// Subscribe to OutputData
Observable.FromEventPattern<DataReceivedEventArgs>(process, nameof(Process.OutputDataReceived))
.Subscribe(
eventPattern => output.AppendLine(eventPattern.EventArgs.Data),
exception => error.AppendLine(exception.Message)
).DisposeWith(disposables);
// Subscribe to ErrorData
Observable.FromEventPattern<DataReceivedEventArgs>(process, nameof(Process.ErrorDataReceived))
.Subscribe(
eventPattern => error.AppendLine(eventPattern.EventArgs.Data),
exception => error.AppendLine(exception.Message)
).DisposeWith(disposables);
var processExited =
// Observable will tick when the process has gracefully exited.
Observable.FromEventPattern<EventArgs>(process, nameof(Process.Exited))
// First two lines to tick true when the process has gracefully exited and false when it has timed out.
.Select(_ => true)
.Timeout(TimeSpan.FromMilliseconds(processTimeOutMilliseconds), Observable.Return(false))
// Force termination when the process timed out
.Do(exitedSuccessfully => { if (!exitedSuccessfully) { try { process.Kill(); } catch {} } } );
// Subscribe to the Process.Exited event.
processExited
.Subscribe()
.DisposeWith(disposables);
// Start process(ing)
process.Start();
process.BeginOutputReadLine();
process.BeginErrorReadLine();
// Wait for the process to terminate (gracefully or forced)
processExited.Take(1).Wait();
logs = output + Environment.NewLine + error;
success = process.ExitCode == 0;
}
}
We already discussed the first part, where we map our events to observables, so we can jump straight to the meaty part. Here we assign our observable to the processExited variable, because we want to use it more than once.
First, when we activate it, by calling Subscribe. And later on when we want to 'await' its first value.
var processExited =
// Observable will tick when the process has gracefully exited.
Observable.FromEventPattern<EventArgs>(process, nameof(Process.Exited))
// First two lines to tick true when the process has gracefully exited and false when it has timed out.
.Select(_ => true)
.Timeout(TimeSpan.FromMilliseconds(processTimeOutMilliseconds), Observable.Return(false))
// Force termination when the process timed out
.Do(exitedSuccessfully => { if (!exitedSuccessfully) { try { process.Kill(); } catch {} } } );
// Subscribe to the Process.Exited event.
processExited
.Subscribe()
.DisposeWith(disposables);
// Start process(ing)
...
// Wait for the process to terminate (gracefully or forced)
processExited.Take(1).Wait();
One of the problems with OP is that it assumes process.WaitForExit(processTimeOutMiliseconds) will terminate the process when it times out. From MSDN:
Instructs the Process component to wait the specified number of milliseconds for the associated process to exit.
Instead, when it times out, it merely returns control to the current thread (i.e. it stops blocking). You need to manually force termination when the process times out. To know when time out has occurred, we can map the Process.Exited event to a processExited observable for processing. This way we can prepare the input for the Do operator.
The code is pretty self-explanatory. If exitedSuccessfully the process will have terminated gracefully. If not exitedSuccessfully, termination will need to be forced. Note that process.Kill() is executed asynchronously, ref remarks. However, calling process.WaitForExit() right after will open up the possibility for deadlocks again. So even in the case of forced termination, it's better to let all disposables be cleaned up when the using scope ends, as the output can be considered interrupted / corrupted anyway.
The try catch construct is reserved for the exceptional case (no pun intended) where you've aligned processTimeOutMilliseconds with the actual time needed by the process to complete. In other words, a race condition occurs between the Process.Exited event and the timer. The possibility of this happening is again magnified by the asynchronous nature of process.Kill(). I've encountered it once during testing.
For completeness, the DisposeWith extension method.
/// <summary>
/// Extension methods associated with the IDisposable interface.
/// </summary>
public static class DisposableExtensions
{
/// <summary>
/// Ensures the provided disposable is disposed with the specified <see cref="CompositeDisposable"/>.
/// </summary>
public static T DisposeWith<T>(this T item, CompositeDisposable compositeDisposable)
where T : IDisposable
{
if (compositeDisposable == null)
{
throw new ArgumentNullException(nameof(compositeDisposable));
}
compositeDisposable.Add(item);
return item;
}
}

The problem is that if you redirect StandardOutput and/or StandardError the internal buffer can become full.
To solve the issues aforementioned you can run the process in separate threads. I do not use WaitForExit, I utilize the process exited event which will return the ExitCode of the process asynchronously ensuring it has completed.
public async Task<int> RunProcessAsync(params string[] args)
{
try
{
var tcs = new TaskCompletionSource<int>();
var process = new Process
{
StartInfo = {
FileName = 'file path',
RedirectStandardOutput = true,
RedirectStandardError = true,
Arguments = "shell command",
UseShellExecute = false,
CreateNoWindow = true
},
EnableRaisingEvents = true
};
process.Exited += (sender, args) =>
{
tcs.SetResult(process.ExitCode);
process.Dispose();
};
process.Start();
// Use asynchronous read operations on at least one of the streams.
// Reading both streams synchronously would generate another deadlock.
process.BeginOutputReadLine();
string tmpErrorOut = await process.StandardError.ReadToEndAsync();
//process.WaitForExit();
return await tcs.Task;
}
catch (Exception ee) {
Console.WriteLine(ee.Message);
}
return -1;
}
The above code is battle tested calling FFMPEG.exe with command line arguments. I was converting mp4 files to mp3 files and doing over 1000 videos at a time without failing. Unfortunately I do not have direct power shell experience but hope this helps.

For the benefit of readers I'm going to divide this to 2 Sections
Section A: Problem & how to handle similar scenarios
Section B: Problem recreation & Solution
Section A: Problem
When this problem happens - process appears in task manager, then
after 2-3sec disappears (its fine), then it waits for timeout and then
exception is thrown System.InvalidOperationException: Process must
exit before requested information can be determined.
& See Scenario 4 below
In your code:
Process.WaitForExit(ProcessTimeOutMiliseconds); With this you're waiting for Process to Timeout or Exit, which ever takes place first.
OutputWaitHandle.WaitOne(ProcessTimeOutMiliseconds)anderrorWaitHandle.WaitOne(ProcessTimeOutMiliseconds); With this you're waiting for OutputData & ErrorData stream read operation to signal its complete
Process.ExitCode == 0 Gets status of process when it exited
Different settings & their caveats:
Scenario 1 (Happy Path): Process completes before the timeout, and thus your stdoutput and stderror also finishes before it and all is well.
Scenario 2: Process, OutputWaitHandle & ErrorWaitHandle timesout however stdoutput & stderror is still being read and completes after time out WaitHandlers. This leads to another exception ObjectDisposedException()
Scenario 3: Process times-out first (19 sec) but stdout and stderror is in action, you wait for WaitHandler's to times out (19 sec), causing a added delay of + 19sec.
Scenario 4: Process times out and code attempts to prematurely query Process.ExitCode resulting in the error System.InvalidOperationException: Process must exit before requested information can be determined.
I have tested this scenario over a dozen times and works fine, following settings have been used while testing
Size of Output stream ranging from 5KB to 198KB by initiating build of about 2-15 projects
Premature timeouts & process exits within the timeout window
Updated Code
.
.
.
process.BeginOutputReadLine();
process.BeginErrorReadLine();
//First waiting for ReadOperations to Timeout and then check Process to Timeout
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");
Logs = output + Environment.NewLine + error;
//To release allocated resource for the Process
process.Close();
return (false, logs);
}
Console.ForegroundColor = ConsoleColor.Green;
Console.WriteLine("Completed On Time");
Logs = output + Environment.NewLine + error;
ExitCode = process.ExitCode.ToString();
// Close frees the memory allocated to the exited process
process.Close();
//ExitCode now accessible
return process.ExitCode == 0 ? (true, logs) : (false, logs);
}
}
finally{}
EDIT:
After hours of playing around with MSBuild I was finally able to reproduce the issue at my system
Section B: Problem Recreation & Solution
MSBuild has -m[:number] switch which
is used to specify the maximum number of concurrent processes to use
when building.
When this is enabled, MSBuild spawns a number of nodes that lives on
even after the Build is complete. Now,
Process.WaitForExit(milliseconds) would wait never exit and
eventually timeout
I was able to solve this in couple of ways
Spawn MSBuild process indirectly through CMD
$path1 = """C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin\MSBuild.exe"" ""C:\Users\John\source\repos\Test\Test.sln"" -maxcpucount:3"
$cmdOutput = cmd.exe /c $path1 '2>&1'
$cmdOutput
Continue to use MSBuild but be sure to set the nodeReuse to False
$filepath = "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin\MSBuild.exe"
$arg1 = "C:\Users\John\source\repos\Test\Test.sln"
$arg2 = "-m:3"
$arg3 = "-nr:False"
Start-Process -FilePath $filepath -ArgumentList $arg1,$arg2,$arg3 -Wait -NoNewWindow
Even If parallel build is not enabled, you could still prevent your process from hanging at WaitForExit by launching the Build via CMD & therefore you do not create a direct dependency on Build process
$path1 = """C:\....\15.0\Bin\MSBuild.exe"" ""C:\Users\John\source\Test.sln"""
$cmdOutput = cmd.exe /c $path1 '2>&1'
$cmdOutput
The 2nd approach is preferred since you do not want too many MSBuild nodes to be lying around.

Not sure if this is your issue, but looking at MSDN there seems to be some weirdness with the overloaded WaitForExit when you are redirecting output asynchronously. MSDN article recommends calling the WaitForExit that takes no arguments after calling the overloaded method.
Docs page located here. Relevant text:
When standard output has been redirected to asynchronous event handlers, it is possible that output processing will not have completed when this method returns. To ensure that asynchronous event handling has been completed, call the WaitForExit() overload that takes no parameter after receiving a true from this overload. To help ensure that the Exited event is handled correctly in Windows Forms applications, set the SynchronizingObject property.
Code modification might look something like this:
if (process.WaitForExit(ProcessTimeOutMiliseconds))
{
process.WaitForExit();
}

Logic to kill a process within a time limit

I want to ensure that my logic is correct here. I want to run a process for timeout seconds, if it runs for longer it should be immediately killed.
The completed flag should reliably indicate whether the process completed as intended, e.g was not killed, and did not crash or throw an exception.
Also, I am not positive if the check to process.HasExited is correct. If process.WaitForExit() returns false and Kill() succeeds, then will process.HasExited always be true? That would be my assumption but I wanted to confirm. Also, what if anything can be done if Kill() fails,
besides just logging?
using (process = new Process())
{
process.EnableRaisingEvents = true;
process.OutputDataReceived += new DataReceivedEventHandler(OnOutputDataReceived);
process.ErrorDataReceived += new DataReceivedEventHandler(OnErrorDataReceived);
process.Exited += new EventHandler(OnExited);
process.StartInfo = startInfo;
process.Start();
process.BeginOutputReadLine();
process.BeginErrorReadLine();
if (!process.WaitForExit(timeout))
{
try
{
process.Kill();
}
catch (Exception e)
{
LogError(e, MethodBase.GetCurrentMethod());
}
finally
{
this.completed = false;
}
}
else
{
if (process.HasExited)
{
this.code = process.ExitCode;
this.completed = true;
}
else
{
this.completed = false;
}
}
}

Yes, the HasExited will always be true in your case.
According to MSDN,
"A value of true for HasExited indicates that the associated process has terminated, either normally or abnormally.[...]A process can terminate independently of your code. If you started the process using this component, the system updates the value of HasExited automatically, even if the associated process exits independently."
However, if your process crashes and terminates before your timeout, then your code will set it as completed anyway. Maybe you should check the exit code, but it can have different meanings for each process:
if (process.ExitCode != 0)
{
this.completed = false;
}
For crashes, there are some approaches here and here, but generally you can't detect crashes for all processes.

We use the following in a .net console app
private void InitTimer()
{
double lInterval = Convert.ToDouble(AppSettings("MaxExecutionTime"));
lInterval = lInterval * 60 * 1000;
tm = new System.Timers.Timer(lInterval); // global timer object
tm.Elapsed += OnTimedEvent;
tm.Enabled = true;
}
public void ThreadProc(object stateinfo)
{
// set error code here
Environment.Exit(0);
}
private void OnTimedEvent(object source, ElapsedEventArgs e)
{
Threading.ThreadPool.QueueUserWorkItem(new Threading.WaitCallback(ThreadProc));
}

In C, you could set an OS alarm using the alarm function. When it expired, a SIGALRM would be sent to your process, which kills it if no handler is set.

You can use this. It is a C# wrapper over the JobObjects functionallity.
The idea behind is (low level outline that is embedded inside the library I mentioned):
Create a job object.
Configure the job object to have a time limit of x seconds.
Create a process and before resuming it assing it to the job object.
Resume the process.
The process will be killed by the operating system when the time passes. YOu usually get notified by a non zero return code, or a callback. The JobObject API itself allows callbacks, not sure about the C# wrapper.
Also using job objects you can restrict memory usage.
On the page I mentioned you can find examples also.
UPDATE
After I wrote the above statements I have found this Kill child process when parent process is killed. They use the JobObjects for another task, but the usage of JobObjects should be the same as for your case.

Process.Start() hangs when running on a background thread

I've been troubleshooting all day. After doing some research and a lot of trial and error, it seems I've been able to narrow down the issue to the fact that my call to process.Start() doesn't work on a timer thread. The code below works when running on the main thread. Put that exact same code in a timer callback, and it hangs. Why? How do I get it to work with a timer?
private static void RunProcess()
{
var process = new Process();
process.StartInfo.FileName = "cmd";
process.StartInfo.Arguments = "/c exit";
process.StartInfo.UseShellExecute = false;
process.StartInfo.RedirectStandardError = true;
process.StartInfo.RedirectStandardInput = true;
process.StartInfo.RedirectStandardOutput = true;
process.Start(); // code hangs here, when running on background thread
process.StandardOutput.ReadToEnd();
process.WaitForExit();
}
EDIT
As a test, I used this exact same code on another laptop, and I experienced the same problem. This is complete code that can be pasted into a console app. process.Start() hangs, but as soon as I hit any key to end, process.Start() completes before the program ends.
private static System.Timers.Timer _timer;
private static readonly object _locker = new object();
static void Main(string[] args)
{
ProcessTest();
Console.WriteLine("Press any key to end.");
Console.ReadKey();
}
private static void ProcessTest()
{
Initialize();
}
private static void Initialize()
{
int timerInterval = 2000;
_timer = new System.Timers.Timer(timerInterval);
_timer.Elapsed += new ElapsedEventHandler(OnTimerElapsed);
_timer.Start();
}
private static void OnTimerElapsed(object sender, ElapsedEventArgs e)
{
if (!Monitor.TryEnter(_locker)) { return; } // Don't let multiple threads in here at the same time.
try
{
RunProcess();
}
finally
{
Monitor.Exit(_locker);
}
}
private static void RunProcess()
{
var process = new Process();
process.StartInfo.FileName = "cmd";
process.StartInfo.Arguments = "/c exit";
process.StartInfo.UseShellExecute = false;
process.StartInfo.RedirectStandardError = true;
process.StartInfo.RedirectStandardInput = true;
process.StartInfo.RedirectStandardOutput = true;
process.Start(); // ** HANGS HERE **
process.StandardOutput.ReadToEnd();
process.WaitForExit();
}

There are a lot of duplicate questions about this problem, none that exactly fits your case. You can see the problem by using the debugger's Debug + Windows + Threads window. Locate the timer thread and double-click it. Look at the Call Stack window to see:
mscorlib.dll!System.Console.InputEncoding.get() + 0x66 bytes
System.dll!System.Diagnostics.Process.StartWithCreateProcess(System.Diagnostics.ProcessStartInfo startInfo) + 0x7f5 bytes
System.dll!System.Diagnostics.Process.Start() + 0x88 bytes
ConsoleApplication70.exe!Program.RunProcess() Line 43 + 0xa bytes C#
ConsoleApplication70.exe!Program.OnTimerElapsed(object sender, System.Timers.ElapsedEventArgs e) Line 28 + 0x5 bytes C#
// etc...
The thread is deadlocked on the Console.InputEncoding property getter. Which is used by the Process class to figure out what encoding needs to be used to translate the redirected output of the process into strings.
This is specific to .NET 4.5, it will also affect apps that target 4.0 on a machine that has 4.5 installed since it is not a side-by-side version of .NET. The deadlock is caused by the Console.ReadKey() method call in your main thread. Which now acquires a lock that prevents other threads from messing with the console. This has been a fairly global change across Microsoft software, the CRT that is used in C/C++ apps created by VS2012 also added this lock. The exact reason isn't that clear to me, but surely has to do something with console output not getting intermingled with console input while your program is asking for input. Exactly why the InputEncoding property needs to take that lock as well is, well, a bit hard to explain but fits the pattern of serializing access to console input. This of course comes as a big surprise to many programmers, especially the ones that write little test apps that test threaded code, like you did. Bit of a setback to TDD.
The workaround is a bit unpleasant, TDD wise, you do have to stop using Console.ReadKey() to avoid the deadlock. Real programs would use the WaitOne() method of an AutoResetEvent to know that the worker thread finished executing. Or CountDownEvent.Wait(), more in keeping with trying out code a couple of times. Etcetera.
UPDATE: this deadlock scenario was resolved in a service update for .NET 4.5. Enable Windows Update on your machine to get it.

Async process start and wait for it to finish

I am new to the thread model in .NET. What would you use to:
Start a process that handles a file (process.StartInfo.FileName = fileName;).
Wait for the user to close the process OR abandon the thread after some time.
If the user closed the process, delete the file.
Starting the process and waiting should be done on a different thread than the main thread, because this operation should not affect the application.
Example:
My application produces an html report. The user can right click somewhere and say "View Report" - now I retrieve the report contents in a temporary file and launch the process that handles html files i.e. the default browser. The problem is that I cannot cleanup, i.e. delete the temp file.

"and waiting must be async" - I'm not trying to be funny, but isn't that a contradiction in terms? However, since you are starting a Process, the Exited event may help:
ProcessStartInfo startInfo = null;
Process process = Process.Start(startInfo);
process.EnableRaisingEvents = true;
process.Exited += delegate {/* clean up*/};
If you want to actually wait (timeout etc), then:
if(process.WaitForExit(timeout)) {
// user exited
} else {
// timeout (perhaps process.Kill();)
}
For waiting async, perhaps just use a different thread?
ThreadPool.QueueUserWorkItem(delegate {
Process process = Process.Start(startInfo);
if(process.WaitForExit(timeout)) {
// user exited
} else {
// timeout
}
});

Adding an advanced alternative to this old question. If you want to wait for a process to exit without blocking any thread and still support timeouts, try the following:
public static Task<bool> WaitForExitAsync(this Process process, TimeSpan timeout)
{
ManualResetEvent processWaitObject = new ManualResetEvent(false);
processWaitObject.SafeWaitHandle = new SafeWaitHandle(process.Handle, false);
TaskCompletionSource<bool> tcs = new TaskCompletionSource<bool>();
RegisteredWaitHandle registeredProcessWaitHandle = null;
registeredProcessWaitHandle = ThreadPool.RegisterWaitForSingleObject(
processWaitObject,
delegate(object state, bool timedOut)
{
if (!timedOut)
{
registeredProcessWaitHandle.Unregister(null);
}
processWaitObject.Dispose();
tcs.SetResult(!timedOut);
},
null /* state */,
timeout,
true /* executeOnlyOnce */);
return tcs.Task;
}
Again, the advantage to this approach compared to the accepted answer is that you're not blocking any threads, which reduces the overhead of your app.

Try the following code.
public void KickOffProcess(string filePath) {
var proc = Process.Start(filePath);
ThreadPool.QueueUserWorkItem(new WaitCallBack(WaitForProc), proc);
}
private void WaitForProc(object obj) {
var proc = (Process)obj;
proc.WaitForExit();
// Do the file deletion here
}

The .NET 5 introduced the new API Process.WaitForExitAsync, that allows to wait asynchronously for the completion of a process. It offers the same functionality with the existing Process.WaitForExit, with the only difference being that the waiting is asynchronous, so it does not block the calling thread.
Usage example:
private async void button1_Click(object sender, EventArgs e)
{
string filePath = Path.Combine
(
Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
Guid.NewGuid().ToString() + ".txt"
);
File.WriteAllText(filePath, "Hello World!");
try
{
using Process process = new();
process.StartInfo.FileName = "Notepad.exe";
process.StartInfo.Arguments = filePath;
process.Start();
await process.WaitForExitAsync();
}
finally
{
File.Delete(filePath);
}
MessageBox.Show("Done!");
}
In the above example the UI remains responsive while the user interacts with the opened file. The UI thread would be blocked if the WaitForExit had been used instead.

I would probably not use a separate process for opening a file. Instead, I'd probably utilize a background thread (if I thought the operation was going to take a long time and possible block the UI thread).
private delegate void FileOpenDelegate(string filename);
public void OpenFile(string filename)
{
FileOpenDelegate fileOpenDelegate = OpenFileAsync;
AsyncCallback callback = AsyncCompleteMethod;
fileOpenDelegate.BeginInvoke(filename, callback, state);
}
private void OpenFileAsync(string filename)
{
// file opening code here, and then do whatever with the file
}
Of course, this is not a good working example (it returns nothing) and I haven't shown how the UI gets updated (you have to use BeginInvoke at the UI level because a background thread cannot update the UI thread). But this approach is generally how I go about handling asynchronous operations in .Net.

You can use the Exited event in Process class
ProcessStartInfo info = new ProcessStartInfo();
info.FileName = "notepad.exe";
Process process = Process.Start(info);
process.Exited += new EventHandler(process_Exited);
Console.Read();
and in that event you can handle the operations you mentioned