Drekar Launch Process

This library contains C# client utility functions for processes launched using drekar-launch, although they may also be used without drekar-launch. Currently this package provides a reliable way for processes to receive shutdown signals from a process manager or the user using ctrl-c.

See drekar-launch: https://github.com/johnwason/drekar-launch

Installation

Install the nuget package DrekarLaunchProcessNET.

Usage

The DrekarLaunchProcessNET library contains one class, DrekarLanchProcess.CWaitForExit. This class contains two functions WaitForExit() and CallbackWaitForExit(Action cb). WaitForExit will block until the shutdown signal is received. CallbackWaitForExit will call the callback cb when the exit signal is received. CWaitForExit implements IDisposable and should be used with a using statement.

Example:

using DrekarLaunchProcess;
using System;

internal class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("Press Ctrl-C to exit");
        using (var wait_for_exit = new CWaitForExit())
        {            
            wait_for_exit.WaitForExit();
        }
        Console.WriteLine("Done");
    }
}

Shutdown Signal Explanation

Reliably sending a shutdown/quit command to a process in a cross-platform manner is surprisingly difficult. On POSIX based systems like Linux and Mac OS X, signals such as SIGINT or SIGTERM are typically sent. (Ctrl-C sends SIGINT). These signals can be caught by the process, and used to gracefully shut down. SIGKILL is used to immediately terminate the process.

On Windows, it is significantly more difficult. Windows typically uses "Window Message Queues" to communicate with processes. Even processes like services that do not have a visible window often have a hidden window so messages can be received from the operating system. There is some functionality for sending console signals, but these are not reliable for all cases. Windows also has the concept of Job Objects that can be used to group different processes together. The combination of job objects and windows messages provide a reliable way to send and receive graceful shutdown signals.

The WaitForExit* commands either way for Signals on POSIX, or windows close messages and console events on Windows.