How to Get CPU Usage of Processes and Threads

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices.ComTypes;
using System.Collections;
using System.Drawing.Drawing2D;
using System.Globalization;

namespace CpuUsageAPI
{
    public partial class Example : Form
    {
        const ProcessData PROCESS_DATA_NOT_FOUND = null;
        const ListViewItem PROCESS_ITEM_NOT_FOUND = null;

        ArrayList ProcessDataList = new ArrayList();
        ArrayList IDList = new ArrayList();
        ListViewItem IdleProcessItem;

        public Example()
        {
            InitializeComponent();

            SetStyle(
                ControlStyles.AllPaintingInWmPaint |
                ControlStyles.ResizeRedraw |
                ControlStyles.DoubleBuffer |
                ControlStyles.UserPaint |
                ControlStyles.SupportsTransparentBackColor,
                true
                );
        }
        // this is where it all happends
        private void GetUsage()
        {
            
            ProcessEntry32 ProcessInfo = new ProcessEntry32();
            ProcessTimes ProcessTimes = new ProcessTimes();
            IntPtr ProcessList, ProcessHandle = ProcessCPU.PROCESS_HANDLE_ERROR;
            ProcessData CurrentProcessData;
            int Index;
            int Total = 0;
            bool NoError;

            // this creates a pointer to the current process list
            ProcessList = ProcessCPU.CreateToolhelp32Snapshot(ProcessCPU.TH32CS_SNAPPROCESS, 0);

            if (ProcessList == ProcessCPU.PROCESS_LIST_ERROR) { return; }

            // we usage Process32First, Process32Next to loop threw the processes
            ProcessInfo.Size = ProcessCPU.PROCESS_ENTRY_32_SIZE;
            NoError = ProcessCPU.Process32First(ProcessList, ref ProcessInfo);
            IDList.Clear();

            ProcessView.SuspendLayout();

            while (NoError)
                try
                {
                    // we need a process handle to pass it to GetProcessTimes function
                    // the OpenProcess function will provide us the handle by the id
                    ProcessHandle = ProcessCPU.OpenProcess(ProcessCPU.PROCESS_ALL_ACCESS, false, ProcessInfo.ID);

                    // here's what we are looking for, this gets the kernel and user time
                    ProcessCPU.GetProcessTimes(
                        ProcessHandle,
                        out ProcessTimes.RawCreationTime,
                        out ProcessTimes.RawExitTime,
                        out ProcessTimes.RawKernelTime,
                        out ProcessTimes.RawUserTime);

                    // convert the values to DateTime values
                    ProcessTimes.ConvertTime();

                    //from here is just managing the gui for the process list
                    CurrentProcessData = ProcessExists(ProcessInfo.ID);
                    IDList.Add(ProcessInfo.ID);

                    if (CurrentProcessData == PROCESS_DATA_NOT_FOUND)
                    {
                        Index = ProcessDataList.Add(new ProcessData(
                            ProcessInfo.ID,
                            ProcessInfo.ExeFilename,
                            ProcessTimes.UserTime.Ticks,
                            ProcessTimes.KernelTime.Ticks));

                        AddProcess((ProcessData) ProcessDataList[Index]);
                    }
                    else
                        Total += CurrentProcessData.UpdateCpuUsage(
                                    ProcessTimes.UserTime.Ticks,
                                    ProcessTimes.KernelTime.Ticks);
                }
                finally
                {
                    if (ProcessHandle != ProcessCPU.PROCESS_HANDLE_ERROR)
                        ProcessCPU.CloseHandle(ProcessHandle);

                    NoError = ProcessCPU.Process32Next(ProcessList, ref ProcessInfo);
                }

            ProcessCPU.CloseHandle(ProcessList);

            Index = 0;

            while (Index < ProcessDataList.Count)
            {
                ProcessData TempProcess = (ProcessData)ProcessDataList[Index];

                if (IDList.Contains(TempProcess.ID))
                    Index++;
                else
                {
                    ProcessView.Items.Remove(TempProcess.ProcessItem);
                    ProcessDataList.RemoveAt(Index);
                }
            }

            IdleProcessItem.SubItems[2].Text = (100 - Total) + "%";

            ProcessView.ResumeLayout();
        }

        private ProcessData ProcessExists(uint ID)
        {
            foreach (ProcessData TempProcess in ProcessDataList)
                if (TempProcess.ID == ID) return TempProcess;

            return PROCESS_DATA_NOT_FOUND;
        }

        private bool ProcessUpdated(uint ID)
        {
            foreach (uint UpdatedProcess in IDList)
                if (UpdatedProcess == ID) return true;

            return false;
        }

        private void UsageTimer_Tick(object sender, EventArgs e)
        {
            GetUsage();
        }

        private void AddProcess(ProcessData NewProcess)
        {
            ListViewItem NewProcessItem = ProcessView.Items.Add(NewProcess.Name);

            NewProcessItem.SubItems.Add(NewProcess.ID.ToString());
            NewProcessItem.SubItems.Add("0%");

            NewProcess.ProcessItem = NewProcessItem;

            if (NewProcess.ID == 0)
                IdleProcessItem = NewProcessItem;
        }
    }
}