Process sometimes hangs while waiting for Exit

Question

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

Answer 1

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:

1. Process.WaitForExit(ProcessTimeOutMiliseconds); With this you're waiting for Process to Timeout or Exit, which ever takes place first.
2. OutputWaitHandle.WaitOne(ProcessTimeOutMiliseconds)anderrorWaitHandle.WaitOne(ProcessTimeOutMiliseconds); With this you're waiting for OutputData & ErrorData stream read operation to signal its complete
3. 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.