Building a macOS app to know when my Mac is thermal throttling

4 months ago

The author built MacThrottle, a macOS app to monitor thermal throttling on M2 MacBook Air, especially when using demanding external displays.
Thermal throttling occurs when the CPU usage is at 100% but power usage drops, making the system slow or unresponsive.
Apple's ProcessInfo.thermalState and powermetrics provide thermal state data, but their granularity and states differ, making ProcessInfo less useful for detecting actual throttling.
The author discovered that thermald writes thermal pressure data to the Darwin notification system (notifyd), allowing access without root privileges.
MacThrottle was built as a SwiftUI menu bar app, showing thermal state via a thermometer icon with color changes from green to red.
Initially, the app used a root helper with powermetrics but later switched to using thermald's IPC notifications for simplicity and security.
Temperature and fan speed data are displayed in a compact graph, with CPU temperature and fan speed (if available) plotted over a 10-minute window.
The app includes macOS notifications for state changes and can be set to launch at login using SMAppService.
Due to lack of notarization, installing the app requires extra steps, and building from source is necessary for some Macs.

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