PressureBar

PressureBar is a lightweight macOS menu bar utility that shows:

• Current CPU usage
• Current memory usage
• Available memory
• Swap usage
• A simplified memory pressure state

The app is designed to stay small and avoid shelling out to tools like top or vm_stat on every refresh.

Features

• Native macOS menu bar app
• No Dock icon
• CPU and memory updates every 1, 2, or 3 seconds
• Default refresh interval set to 3 seconds to minimize runtime overhead
• Optional launch-at-login toggle
• Compact menu bar label like C16% M84%
• Detail panel with system stats
• Pressure states: Low, Medium, High

Project Structure

• pressurebar/ SwiftUI app source
• pressurebar.xcodeproj/ Xcode project

Requirements

• macOS 14.6 or newer
• Xcode 26 or newer

Supported macOS Version

PressureBar currently targets:

• macOS 14.6+

This keeps the app compatible with modern macOS versions while still avoiding an unnecessarily high minimum deployment target.

How To Run

Option 1: Run from Xcode

1. Open pressurebar.xcodeproj in Xcode.
2. Select the pressurebar scheme.
3. Choose My Mac as the run destination.
4. Press Run.

Because PressureBar is configured as a menu bar utility, it does not open a normal window and does not appear in the Dock. After launch, look for the app in the macOS menu bar.

If Xcode asks for signing:

1. Open the pressurebar target.
2. Go to Signing & Capabilities.
3. Choose your Apple team for local development.
4. Run again.

Option 2: Build from Terminal

For a local unsigned build:

xcodebuild \
  -project pressurebar.xcodeproj \
  -scheme pressurebar \
  -configuration Debug \
  -derivedDataPath /tmp/pressurebar-derived \
  CODE_SIGNING_ALLOWED=NO \
  CODE_SIGNING_REQUIRED=NO \
  build

This is useful for validation, but for normal day-to-day use the easiest path is still running from Xcode with local signing enabled.

How To Quit

• Open the PressureBar menu from the menu bar.
• Click Quit PressureBar.

If the process stays running during development, you can also stop it from Terminal:

pkill -x pressurebar

Distribution

For public distribution, the recommended path is:

1. Sign the app with Developer ID Application
2. Keep Hardened Runtime enabled
3. Notarize the final artifact with Apple
4. Publish a notarized .zip or .dmg in GitHub Releases

For a first release, a notarized .zip is the simplest option. A .dmg gives a nicer installation experience and is a good next step.

Availability

PressureBar is available on the Mac App Store:

• PressureBar on the App Store

How The Calculations Work

PressureBar uses native macOS APIs from Mach and sysctl, not external command-line tools.

CPU Usage

CPU usage is calculated from host_processor_info using PROCESSOR_CPU_LOAD_INFO.

The app stores the previous CPU sample and compares it with the current sample:

• totalDelta = currentTotalTicks - previousTotalTicks
• idleDelta = currentIdleTicks - previousIdleTicks
• busyDelta = totalDelta - idleDelta
• cpuUsage = busyDelta / totalDelta

This produces a system-wide CPU usage percentage over the refresh interval.

Memory Usage

Memory values come from host_statistics64 with HOST_VM_INFO64.

PressureBar currently uses:

• freeBytes = free_count * pageSize
• cachedBytes = external_page_count * pageSize
• availableBytes = freeBytes + cachedBytes
• usedBytes = totalPhysicalMemory - availableBytes

This choice is intentional:

• free memory reflects immediately unused pages
• external_page_count maps more closely to reclaimable cached memory
• using free + cached makes the result align more closely with Activity Monitor than using inactive_count

Swap Usage

Swap is read from:

• sysctlbyname("vm.swapusage", ...)

The displayed value is xsu_used.

Pressure States

PressureBar exposes a simplified pressure signal with three states.

Low

Shown when the system still has comfortable headroom.

Current rule:

• headroom >= 18%
• or swap exists but there is still enough free/cached memory

Medium

Shown when available memory is getting tighter, but the system is not yet in the most constrained state.

Current rule:

• headroom < 18%
• or swap > 0 and headroom < 28%

High

Shown when headroom is critically low, or when low headroom and heavy swap usage happen together.

Current rule:

• headroom < 6%
• or headroom < 10% and swapRatio > 0.5

Where:

• headroom = availableBytes / totalBytes
• swapRatio = swapUsedBytes / totalBytes

Notes On Accuracy

PressureBar is intentionally pragmatic rather than a perfect clone of Activity Monitor.

What it tries to do well:

• stay lightweight
• use native system APIs
• provide values that track Activity Monitor closely enough to be useful in real time

What it does not try to do yet:

• reproduce Apple's exact internal memory pressure model
• expose every VM category shown by Activity Monitor

Future Improvements

• Launch at login
• Configurable menu bar text format
• More detailed memory breakdown
• Better historical trend display
• Fine-tuned pressure heuristics based on more real-world comparisons