System State

System State

Dapplo.Windows.SystemState provides modern, idiomatic C# APIs for controlling and monitoring the Windows power state — sleep, hibernate, shutdown, restart, logoff, workstation lock, thread execution state, and scheduled wake-up timers.

Package: Dapplo.Windows.SystemState

Install-Package Dapplo.Windows.SystemState

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In This Page

• Putting the System to Sleep or Hibernate
• Shutdown, Restart, and Logoff
• Locking the Workstation
• Thread Execution State — Preventing Sleep
• WaitableTimer — Scheduled Wake-Up
• PowerBroadcastListener — Reacting to Power Events
• Combining Wake Timers with Power Events

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Putting the System to Sleep or Hibernate

PowerManagementApi.Sleep() and PowerManagementApi.Hibernate() wrap SetSuspendState from powrprof.dll.

using Dapplo.Windows.SystemState;

// Put the system to sleep (suspend to RAM)
PowerManagementApi.Sleep();

// Hibernate (suspend to disk)
PowerManagementApi.Hibernate();

// Sleep but disable any previously scheduled wake events
PowerManagementApi.Sleep(disableWakeEvent: true);

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Shutdown, Restart, and Logoff

PowerManagementApi wraps ExitWindowsEx from user32.dll.

Shutdown and reboot require the SE_SHUTDOWN_NAME privilege.

using Dapplo.Windows.SystemState;

PowerManagementApi.LogOff();
PowerManagementApi.Shutdown();
PowerManagementApi.Restart();

// Force close hung applications before shutting down
PowerManagementApi.Shutdown(force: true);

// Raw call with explicit flags
using Dapplo.Windows.SystemState.Enums;

PowerManagementApi.ExitWindowsEx(
    ExitWindowsFlags.EWX_SHUTDOWN | ExitWindowsFlags.EWX_FORCEIFHUNG);

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Locking the Workstation

using Dapplo.Windows.SystemState;

// Equivalent to pressing Win+L
PowerManagementApi.LockWorkStation();

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Thread Execution State — Preventing Sleep

SystemStateApi wraps SetThreadExecutionState from kernel32.dll.

using Dapplo.Windows.SystemState;

// Prevent the system AND screen from sleeping while a task runs
SystemStateApi.PreventSleep();
DoLongRunningWork();
SystemStateApi.AllowSleep(); // always restore when done

// Prevent only the system from sleeping (screen may still turn off)
SystemStateApi.PreventSystemSleep();
DoBackgroundSync();
SystemStateApi.AllowSleep();

Method	Flags Set
PreventSleep()	ES_CONTINUOUS | ES_SYSTEM_REQUIRED | ES_DISPLAY_REQUIRED
PreventSystemSleep()	ES_CONTINUOUS | ES_SYSTEM_REQUIRED
AllowSleep()	ES_CONTINUOUS (clears all other flags)

Always call AllowSleep() when finished — if you forget, the system will not sleep until your process exits.

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WaitableTimer — Scheduled Wake-Up

WaitableTimer is a managed IDisposable wrapper around the kernel32 waitable timer APIs (CreateWaitableTimer, SetWaitableTimer, CancelWaitableTimer).

One-Shot (relative delay)

using var timer = new WaitableTimer();

timer.SetOnce(TimeSpan.FromMinutes(30));
bool fired = timer.Wait(TimeSpan.FromHours(1));

One-Shot (absolute UTC time)

using var timer = new WaitableTimer();

timer.SetAt(DateTimeOffset.UtcNow.AddHours(6));
timer.Wait(TimeSpan.FromHours(7));

Periodic timer

using var timer = new WaitableTimer();

// Start in 1 second, repeat every 10 seconds
timer.SetPeriodic(TimeSpan.FromSeconds(1), period: 10_000);

for (int i = 0; i < 5; i++)
{
    timer.Wait(TimeSpan.FromSeconds(15));
    DoPeriodicWork();
}

timer.Cancel();

System Wake-Up

Pass wakeSystem: true to schedule the system to wake from sleep or hibernate when the timer fires. This requires the SE_SYSTEMTIME_NAME privilege (typically available to elevated processes and services).

using var timer = new WaitableTimer();

// Wake the PC in 2 hours (even if it is sleeping)
timer.SetOnce(TimeSpan.FromHours(2), wakeSystem: true);
timer.Wait(TimeSpan.FromHours(3));
Console.WriteLine("System woke up");

See also: System Wake-Up Events (Microsoft Docs)

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PowerBroadcastListener — Reacting to Power Events

PowerBroadcastListener exposes WM_POWERBROADCAST messages as IObservable<PowerBroadcastEvent> streams. It is built on top of SharedMessageWindow and requires no extra registration step.

Available on net480, net8.0-windows, net10.0-windows only (not netstandard2.0).

using Dapplo.Windows.SystemState;
using Dapplo.Windows.SystemState.Enums;

// React just before the system suspends
var suspendSub = PowerBroadcastListener.Suspending
    .Subscribe(_ => FlushApplicationState());

// React when the user wakes the PC
var resumeSub = PowerBroadcastListener.ResumedFromSuspend
    .Subscribe(_ => ReconnectServices());

// React to a programmatic (timer-triggered) wake — no user present
var autoResumeSub = PowerBroadcastListener.ResumedAutomatically
    .Subscribe(_ => PerformScheduledBackgroundTask());

// React to AC/battery power source changes
var powerStatusSub = PowerBroadcastListener.PowerStatusChanged
    .Subscribe(_ => UpdateBatteryIndicator());

// Filter the full event stream for anything not covered above
var allSub = PowerBroadcastListener.PowerEvents
    .Subscribe(e => Log.Info($"Power event: {e}"));

// Dispose subscriptions when done
suspendSub.Dispose();
resumeSub.Dispose();
autoResumeSub.Dispose();
powerStatusSub.Dispose();
allSub.Dispose();

Available Observables

Property	Event(s) filtered
PowerEvents	All WM_POWERBROADCAST events
Suspending	PBT_APMSUSPEND
ResumedFromSuspend	PBT_APMRESUMESUSPEND
ResumedAutomatically	PBT_APMRESUMEAUTOMATIC
PowerStatusChanged	PBT_APMPOWERSTATUSCHANGE

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Combining Wake Timers with Power Events

A common pattern is to schedule work to run on a wake-timer event:

using Dapplo.Windows.SystemState;
using System.Reactive.Linq;

// 1. Subscribe to the automatic resume event BEFORE setting the timer
var wakeHandlerSub = PowerBroadcastListener.ResumedAutomatically
    .Take(1) // handle only the next automatic resume
    .Subscribe(_ =>
    {
        Console.WriteLine("Wake timer fired — performing backup");
        PerformNightlyBackup();
    });

// 2. Schedule the wake-up
using var timer = new WaitableTimer();
timer.SetAt(DateTimeOffset.UtcNow.Date.AddDays(1).AddHours(3), wakeSystem: true); // 3 AM tomorrow

// 3. Optionally sleep the system now
PowerManagementApi.Sleep();

// 4. Dispose when no longer needed
wakeHandlerSub.Dispose();

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See Also

• SharedMessageWindow — powers PowerBroadcastListener
• Restart-Manager — react to WM_QUERYENDSESSION / WM_ENDSESSION
• Common-Scenarios
• WM_POWERBROADCAST (Microsoft Docs)
• SetSuspendState (Microsoft Docs)
• SetThreadExecutionState (Microsoft Docs)
• System Wake-Up Events (Microsoft Docs)