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Wake the PC from standby or hibernation

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3 Feb 2014CPOL2 min read 181.8K   4.6K   119   64
How to automatically wake up the PC at some time in the future.

Introduction

Sometimes, it might be useful to automatically turn on the PC at some time in the future. To do this, we'll use a little trick: usually, a computer is not capable of powering itself up, but it's able to recover from standby or hibernation (if the hardware is capable of it).

Background

The code is mainly a wrapper around two system timer functions: CreateWaitableTimer and SetWaitableTimer. That's because the timer is able to resume the system, if told to. The declaration is:

C#
[DllImport("kernel32.dll")]
public static extern SafeWaitHandle CreateWaitableTimer(IntPtr lpTimerAttributes, 
                                                          bool bManualReset,
                                                        string lpTimerName);

[DllImport("kernel32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool SetWaitableTimer(SafeWaitHandle hTimer, 
                                            [In] ref long pDueTime, 
                                                      int lPeriod,
                                                   IntPtr pfnCompletionRoutine, 
                                                   IntPtr lpArgToCompletionRoutine, 
                                                     bool fResume);

We need to provide a date and a time, but SetWaitableTimer asks for a long integer value... DateTime.ToFileTime() is the function that we'll use to convert date/times from managed to system representations. 

Take a look at the core of the program, where we call the two API functions: 

C#
long waketime = (long)e.Argument;

using (SafeWaitHandle handle = 
         CreateWaitableTimer(IntPtr.Zero, true, 
         this.GetType().Assembly.GetName().Name.ToString() + "Timer"))
{
    if (SetWaitableTimer(handle, ref waketime, 0, 
                         IntPtr.Zero, IntPtr.Zero, true))
    {
        using (EventWaitHandle wh = new EventWaitHandle(false, 
                                             EventResetMode.AutoReset))
        {
            wh.SafeWaitHandle = handle;
            wh.WaitOne();
        }
    }
    else
    {
        throw new Win32Exception(Marshal.GetLastWin32Error());
    }
}

You can notice an "e.Argument" in the first line. It's there because the following block of code pauses the execution of the thread until the timer reaches the "wake time" value:

C#
using (EventWaitHandle wh = new EventWaitHandle(false, 
                                EventResetMode.AutoReset))
{
    wh.SafeWaitHandle = handle;
    wh.WaitOne();
}

So, to avoid blocking the UI thread, we need to put that block of code into a separate thread, controlled by a BackgroundWorker object to which we'll pass the wake time as an argument. This is where "e.Argument" comes from.

I needed to create a class for easy re-use, so I decided to provide an event: "Woken". The event gets triggered as soon as the background thread exits:

C#
public event EventHandler Woken;

void bgWorker_RunWorkerCompleted(object sender, 
              RunWorkerCompletedEventArgs e)
{
    if (Woken != null)
    {
        Woken(this, new EventArgs());
    }
}

So, to recap, this is the full class: 

C#
using System;
using System.Text;
using System.Runtime.InteropServices;
using Microsoft.Win32.SafeHandles;
using System.ComponentModel;
using System.Threading;

namespace WakeUPTimer
{
    class WakeUP
    {
        [DllImport("kernel32.dll")]
        public static extern SafeWaitHandle CreateWaitableTimer(IntPtr lpTimerAttributes, 
                                                                  bool bManualReset,
                                                                string lpTimerName);

        [DllImport("kernel32.dll", SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool SetWaitableTimer(SafeWaitHandle hTimer, 
                                                    [In] ref long pDueTime, 
                                                              int lPeriod,
                                                           IntPtr pfnCompletionRoutine, 
                                                           IntPtr lpArgToCompletionRoutine, 
                                                             bool fResume);

        public event EventHandler Woken;

        private BackgroundWorker bgWorker = new BackgroundWorker();

        public WakeUP()
        {
            bgWorker.DoWork += new DoWorkEventHandler(bgWorker_DoWork);
            bgWorker.RunWorkerCompleted += 
              new RunWorkerCompletedEventHandler(bgWorker_RunWorkerCompleted);
        }

        public void SetWakeUpTime(DateTime time)
        {
            bgWorker.RunWorkerAsync(time.ToFileTime());
        }

        void bgWorker_RunWorkerCompleted(object sender, 
                      RunWorkerCompletedEventArgs e)
        {
            if (Woken != null)
            {
                Woken(this, new EventArgs());
            }
        }

        private void bgWorker_DoWork(object sender, DoWorkEventArgs e) 
        {
            long waketime = (long)e.Argument;

            using (SafeWaitHandle handle = 
                      CreateWaitableTimer(IntPtr.Zero, true, 
                      this.GetType().Assembly.GetName().Name.ToString() + "Timer"))
            {
                if (SetWaitableTimer(handle, ref waketime, 0, 
                                       IntPtr.Zero, IntPtr.Zero, true))
                {
                    using (EventWaitHandle wh = new EventWaitHandle(false, 
                                                           EventResetMode.AutoReset))
                    {
                        wh.SafeWaitHandle = handle;
                        wh.WaitOne();
                    }
                }
                else
                {
                    throw new Win32Exception(Marshal.GetLastWin32Error());
                }
            }
        }

    }
}

Using the Code

If we have a Button and a DateTimePicker on a form, we can write something like this:

C#
private void button1_Click(object sender, EventArgs e)
{
    WakeUP wup = new WakeUP();
    wup.Woken += WakeUP_Woken;
    wup.SetWakeUpTime(dateTimePicker1.Value);
}

private void WakeUP_Woken(object sender, EventArgs e)
{
    // Do something 
}

And to suspend the system:

C#
Application.SetSuspendState(PowerState.Suspend, false, false);

Important note: the last parameter, disableWakeEvent, needs to be false.

Troubleshooting

If the software doesn't work, it doesn't necessarily mean that your hardware doesn't support it. It's possible that some Windows setting is preventing the awakening of the system. To make sure that the settings are correct, check that: 

  • In "Control Panel > Power Options > Change Plan Settings > Change Advanced Power Settings > Sleep > Allow Wake Timers", all items are enabled.
  • If there is no password set on your Windows account, make sure that in "Control Panel > Power Options > Change Plan Settings > Change Advanced Power Settings > Brad / Additional Settings > Require a password on wakeup", all items are disabled (thanks nanfang).

Points of Interest

I used a BackgroundWorker for a simple reason: the code in the Woken event must be in the same thread of the user interface for easy access to controls. With standard thread management, that's not so trivial.

History

  • v1.0 - 2009/12/31 - Initial release.
  • v1.1 - 2010/10/03 - Fixed a bug and updated article (troubleshooting section).

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


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Comments and Discussions

 
GeneralWorks Great Pin
Prasad_MCA15-Aug-11 7:28
Prasad_MCA15-Aug-11 7:28 
GeneralThe BackgroundWorker is busy Pin
hnldp2sh10-Mar-11 15:34
hnldp2sh10-Mar-11 15:34 
GeneralRe: The BackgroundWorker is busy Pin
Daniele Di Sarli11-Mar-11 4:50
Daniele Di Sarli11-Mar-11 4:50 
GeneralRe: The BackgroundWorker is busy Pin
h3mp17-Oct-13 1:25
h3mp17-Oct-13 1:25 
GeneralWorks very well with standby and hibernate [modified] Pin
gauravkale22-Feb-11 4:00
gauravkale22-Feb-11 4:00 
GeneralRe: Works very well with standby and hibernate Pin
Daniele Di Sarli22-Feb-11 8:19
Daniele Di Sarli22-Feb-11 8:19 
GeneralScreen stays black Pin
Pascal Hubert18-Jan-11 5:28
Pascal Hubert18-Jan-11 5:28 
GeneralRe: Screen stays black Pin
Daniele Di Sarli18-Jan-11 5:38
Daniele Di Sarli18-Jan-11 5:38 
GeneralRe: Screen stays black Pin
Daniele Di Sarli18-Jan-11 5:43
Daniele Di Sarli18-Jan-11 5:43 
GeneralRe: Screen stays black Pin
Pascal Hubert18-Jan-11 6:03
Pascal Hubert18-Jan-11 6:03 
GeneralRe: Screen stays black Pin
Daniele Di Sarli18-Jan-11 6:56
Daniele Di Sarli18-Jan-11 6:56 
GeneralRe: Screen stays black Pin
Pascal Hubert27-Jan-11 10:32
Pascal Hubert27-Jan-11 10:32 
GeneralRe: Screen stays black Pin
Daniele Di Sarli27-Jan-11 10:53
Daniele Di Sarli27-Jan-11 10:53 
GeneralRe: Screen stays black Pin
Si.Jinmin26-Apr-12 20:34
Si.Jinmin26-Apr-12 20:34 
QuestionI want to write an event when the machine wakes up. How to go about it Pin
digvijay_nath11-Oct-10 17:16
digvijay_nath11-Oct-10 17:16 
AnswerRe: I want to write an event when the machine wakes up. How to go about it [modified] Pin
Karthik. A11-Oct-10 18:48
Karthik. A11-Oct-10 18:48 
GeneralIt works on Windows Vista Ultimate x64 Pin
hswear33-Oct-10 8:40
hswear33-Oct-10 8:40 
GeneralRe: It works on Windows Vista Ultimate x64 Pin
Daniele Di Sarli3-Oct-10 10:06
Daniele Di Sarli3-Oct-10 10:06 
AnswerRe: It works on Windows Vista Ultimate x64 Pin
digvijay_nath11-Oct-10 17:19
digvijay_nath11-Oct-10 17:19 
GeneralRe: It works on Windows Vista Ultimate x64 Pin
Daniele Di Sarli12-Oct-10 5:23
Daniele Di Sarli12-Oct-10 5:23 
GeneralExcellent!!! Pin
Shanthi Diana22-Aug-10 9:32
Shanthi Diana22-Aug-10 9:32 
GeneralRe: Excellent!!! Pin
Daniele Di Sarli23-Aug-10 3:38
Daniele Di Sarli23-Aug-10 3:38 
GeneralIt doesn't work for me Pin
nanfang25-Jul-10 9:45
nanfang25-Jul-10 9:45 
GeneralRe: It doesn't work for me Pin
Daniele Di Sarli25-Jul-10 10:07
Daniele Di Sarli25-Jul-10 10:07 
GeneralRe: It doesn't work for me Pin
nanfang26-Jul-10 17:47
nanfang26-Jul-10 17:47 

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