My code is causing high CPU usage in WMI Provider host (WmiPrvSE.exe)

Question

I've build a project in C# which at some point has to listen to a other file opening and closing. The code i use actually works but somehow every time i run my project "WMI Provider Host" will go crazy with CPU usage. First run it will hit 50% usage and each time i restart my project it will go up by like 10% until it hits 100%. I am not sure if i did something wrong in my code.

I tried putting that function into a new, clean file only to find out the same results.

This is what it looks like:

using System;
using System.Threading;
using System.Management;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {

            string startEventName = "InstanceCreationEvent";
            string stopEventName = "InstanceDeletionEvent";
            string processName = "notepad.exe";

            ListenForProcess(processName, startEventName, (sender, e) =>
            {
                Console.WriteLine("Process Started");
            });

            ListenForProcess(processName, stopEventName, (sender, e) =>
            {
                Console.WriteLine("Process Stopped");
            });

        }

        static void ListenForProcess(string processName,
        string eventName, EventArrivedEventHandler eventHandler)
        {

        string queryString =
        $@"SELECT TargetInstance
        FROM __{eventName}
        WITHIN 0.1
        WHERE TargetInstance ISA 'Win32_Process'
        AND TargetInstance.Name='{processName}'";

            using (var watcher = new ManagementEventWatcher(queryString))
            {
                watcher.EventArrived += eventHandler;
                watcher.Start();

                new Thread(() =>
                {
                    while (true)
                    {
                        watcher.WaitForNextEvent();
                    }
                }).Start();
            }
        }

    }
}

I'm not sure why this is bugging WMI with it's CPU usage.

Only reference added is "System Management".

Any one here having any suggestions or know why this is happening? Thanks!

Answer 1

You should not mix Start() with WaitForNextEvent(). Probalby Start() will also start a background thread that waits for the same event, so mixing both approaches can cause weird side-effects.

So either:

Use EventArrived with Start() (async usage):

var watcher = new ManagementEventWatcher(queryString);
watcher.EventArrived += eventHandler;
watcher.Start();
...
watcher.Stop();

Or, use WaitForNextEvent (sync usage):

var watcher = new ManagementEventWatcher(queryString);
var event = watcher.WaitForNextEvent();
...
watcher.Stop();