关于SYSTEM_POWER_INFORMATION中MaxIdlenessAllowed与TimeRemaining的技术问询

Let's unpack the behavior you're seeing with MaxIdlenessAllowed and TimeRemaining from the SystemPowerInformation struct, based on Windows power management internals:

1. MaxIdlenessAllowed Always Being 0 #

This field is defined as the maximum idle time (in seconds) the system allows before shifting to a lower power state. Here's why it's stuck at 0 for your devices:

• Dynamic Power Management Overhaul: Starting with Windows 8 and continuing in Windows 10, Microsoft replaced fixed idle thresholds with a dynamic power policy engine. This engine adjusts idle behavior in real time based on CPU load, device activity, and power plan settings—so the static MaxIdlenessAllowed value is no longer used, hence returning 0.
• Connected Standby Compatibility: If your devices use Connected Standby (common in modern laptops/tablets), this field is hardcoded to 0. Connected Standby uses activity-based triggers (like sensor input or app notifications) instead of fixed idle timeouts to manage power states.
• No User-Configurable Setting: This value isn't tied to standard power plan options. Even if you adjust sleep/hibernation timeouts in your power settings, MaxIdlenessAllowed will remain 0 because it's no longer part of the active power management logic.

2. TimeRemaining Mostly Showing 4294967295 #

That number is the maximum value for a 32-bit unsigned integer (0xFFFFFFFF), and it translates to "the system cannot estimate remaining idle time until a power state change". Here's the breakdown:

• AC Power Default Behavior: When plugged into AC power, most default power plans either have no automatic sleep timeout or set it to an extremely long duration. Since the system can't predict when you'll resume activity, it returns the "unknown" value.
• Missing Power Plan Configuration: If you haven't explicitly set a sleep/hibernation timeout in your power plan, the system has no target time to count down from—so it can't provide a meaningful TimeRemaining value.
• SetThreadExecutionState Impact: Apps using this function reset the idle timer to prevent the system from entering sleep, but this doesn't alter TimeRemaining. The function tells the system "don't enter idle mode yet," so there's no active countdown to a power transition, hence the system still returns 0xFFFFFFFF.
• Rare Lower Values: The times you see a smaller number are when the system can accurately predict the time until a power state change. For example:
  • Your device is on battery power with a short sleep timeout configured.
  • The system has detected sustained idle activity and is actively counting down to the sleep trigger.

Why Idling Mouse/Keyboard Doesn't Change TimeRemaining #

Idle input devices alone won't trigger a change unless your power plan is set to initiate a power transition after a specific idle period. If your plan lacks this setting (or you're on AC power), the system still can't estimate a valid remaining time, so it sticks with 0xFFFFFFFF.

内容的提问来源于stack exchange，提问作者fulvio