Request suspend on Vista but allow other applications to cancel

Question

My application uses the Win32 SetSuspendState() API to trigger system suspend or hibernation when it has finished doing a lengthy task.

The API accepts a parameter "ForceCritical" which determines whether or not the system suspends immediately or whether it broadcasts PBT_APMQUERYSUSPEND first to allow other apps the chance to cancel the suspend. My app uses this to play nicely with other apps like Media Player, so it doesn't suspend if you're listening to music or something.

For some reason, starting with Vista, MS have changed things so this parameter is ignored so SetSuspendState immediately causes a suspend and other applications have no opportunity to stop it.

Does anyone know how I can get the desired "polite" behaviour back again on Vista?

Answer 1

MSDN says

To prevent the system from transitioning to a low-power state in Windows Vista, an application must call SetThreadExecutionState to inform the system that it is in use

I would guess that WMP does this, but older apps don't. You could probably emulate this by sending the WM_POWERBROADCAST:PBT_APMQUERYSUSPEND message to all top level windows and check their return values (Send the message with a timeout so a hung app does not hang your app)