Question

My app needs to block sleep/hibernate mode. I have the code in place, but after successfully catching the WM_POWERBROADCAST message, neither PBT_APMQUERYSUSPEND nor PBT_APMQUERYSTANDBY are being caught successfully. Interestingly, the PBT_APMRESUMECRITICAL and PBT_APMRESUMEAUTOMATIC messages are being caught by my app.

Bottom line question: is there any reason why my app would fail to catch the standby/suspend messages, but succeed in catching the resume messages?

This Q&A [stackoverflow.com] helped, btw, but again, the messages don’t seem to be making it to my app.

My code (w/ event logging code removed for brevity):

        protected override void WndProc(ref System.Windows.Forms.Message m)
    {
        // Power status event triggered
        if (m.Msg == (int)NativeMethods.WindowMessage.WM_POWERBROADCAST)
        {
            // Machine is trying to enter suspended state
            if (m.WParam.ToInt32() == (int)NativeMethods.WindowMessage.PBT_APMQUERYSUSPEND ||
                m.WParam.ToInt32() == (int)NativeMethods.WindowMessage.PBT_APMQUERYSTANDBY)
            {
                // Have perms to deny this message?
                if((m.LParam.ToInt32() & 0x1) != 0)
                {
                    // If so, deny broadcast message
                    m.Result = new IntPtr((int)NativeMethods.WindowMessage.BROADCAST_QUERY_DENY);
                }
            }
            return; // ?!
        }

        base.WndProc(ref m);
    }

Answer 1

It works now, for both XP and Vista. I created a stub winform app with the relevant code (could be cleaned up, obviously, but it conveys the point).

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace standbyTest
{
    public partial class Form1 : Form
    {

        [DllImport("Kernel32.DLL", CharSet = CharSet.Auto, SetLastError = true)]
        protected static extern EXECUTION_STATE SetThreadExecutionState(EXECUTION_STATE state);

        [Flags]
        public enum EXECUTION_STATE : uint
        {
            ES_CONTINUOUS = 0x80000000,
            ES_DISPLAY_REQUIRED = 2,
            ES_SYSTEM_REQUIRED = 1,
            ES_AWAYMODE_REQUIRED = 0x00000040
        }

        public Form1()
        {
            if(Environment.OSVersion.Version.Major > 5)
            {
                // vista and above: block suspend mode
                SetThreadExecutionState(EXECUTION_STATE.ES_AWAYMODE_REQUIRED | EXECUTION_STATE.ES_SYSTEM_REQUIRED | EXECUTION_STATE.ES_CONTINUOUS);
            }

            InitializeComponent();

            //MessageBox.Show(string.Format("version: {0}", Environment.OSVersion.Version.Major.ToString() ));

        }

        protected override void OnClosed(EventArgs e)
        {
            base.OnClosed(e);

            if(Environment.OSVersion.Version.Major > 5)
            {
                // Re-allow suspend mode
                SetThreadExecutionState(EXECUTION_STATE.ES_CONTINUOUS);
            }
        }


        protected override void WndProc(ref System.Windows.Forms.Message m)
        {
            // Power status event triggered
            if(m.Msg == (int)WindowMessage.WM_POWERBROADCAST)
            {
                // Machine is trying to enter suspended state
                if(m.WParam.ToInt32() == (int)WindowMessage.PBT_APMQUERYSUSPEND ||
                        m.WParam.ToInt32() == (int)WindowMessage.PBT_APMQUERYSTANDBY)
                {
                    // Have perms to deny this message?
                    if((m.LParam.ToInt32() & 0x1) != 0)
                    {
                        // If so, deny broadcast message
                        m.Result = new IntPtr((int)WindowMessage.BROADCAST_QUERY_DENY);
                    }
                }
                return;
            }

            base.WndProc(ref m);
        }
    }



    internal enum WindowMessage
    {

        /// <summary>
        /// Notify that machine power state is changing
        /// </summary>
        WM_POWERBROADCAST = 0x218,
        /// <summary>
        /// Message indicating that machine is trying to enter suspended state
        /// </summary>
        PBT_APMQUERYSUSPEND = 0x0,
        PBT_APMQUERYSTANDBY = 0x0001,

        /// <summary>
        /// Message to deny broadcast query
        /// </summary>
        BROADCAST_QUERY_DENY = 0x424D5144


    }
}