Home/ Questions/Q 173539
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-11T13:21:42+00:00

First time poster, be gentle ;-) I’m writing an audio app (in C++) which

  • 0

First time poster, be gentle 😉

I’m writing an audio app (in C++) which runs as a Windows service, uses WASAPI to take samples from the line in jack, and does some processing on it.

Something I’ve noticed is that when my app is ‘recording’, Windows won’t automatically suspend or hibernate.

I’ve registered for power event notifications and, if I push the suspend button myself, my service gets the appropriate power events and handles them ok. If I leave the system to suspend on its own, the power events are never received.

If I remove the bits of code where I reference WASAPI, the power events are received as normal on both manual and automatic suspend. So it seems like there’s something about using WASAPI that tells Windows to ignore the automatic suspend timer.

Can anyone help explain this behavior, and is there anything I can do to stop it? I don’t want my app to be one of those which misbehaves and prevents systems from suspending..

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Many thanks to Larry for confirming this behaviour is by design and not me doing something silly.

    To work around this issue I used the Win32 CallNtPowerInformation() API to retrieve the system idle timer:

    SYSTEM_POWER_INFORMATION spi = {0}; NTSTATUS status = CallNtPowerInformation(SystemPowerInformation, NULL, 0,                                           &spi, sizeof(spi));  if (NT_SUCCESS(status) && (spi.TimeRemaining==0)) {     // should have gone to sleep }

    The spi.TimeRemaining member counts down (in seconds) from the time specified by the user in Control Panel e.g. ‘System standby after 1 hour’, and gets reset whenever CPU usage (as a percentage) rises above spi.MaxIdlenessAllowed.

    If spi.TimeRemaining ever reaches zero, the system should have gone to sleep, so I close all my WASAPI handles and let it do so.

    • 0