Android Framework Services Overview

Every time you open an app, receive a notification, adjust brightness, or unlock your phone - a framework service is involved. These services run inside System Server (the most critical process in Android) and expose their functionality to apps via Binder IPC.

System Server - The Host Process

  ┌─────────────────────────────────────────────────────┐
  │                  System Server                      │
  │                                                     │
  │  ActivityManagerService   WindowManagerService      │
  │  PackageManagerService    PowerManagerService       │
  │  InputManagerService      NotificationManager       │
  │  LocationManagerService   TelephonyManager          │
  │  AlarmManagerService      JobSchedulerService       │
  │  ContentResolver          AccountManagerService     │
  │                                                     │
  │  All registered with ServiceManager (Binder)        │
  └───────────────────────────┬─────────────────────────┘
                              │  Binder IPC
              ┌───────────────┴───────────────┐
              ▼                               ▼
        App Process A                   App Process B
        (calls via proxy)               (calls via proxy)

Core Services and What They Do

• ▸ActivityManagerService (AMS) - manages the entire app lifecycle (create, start, resume, pause, stop, destroy Activities). Controls the back stack and task management. Handles ANR detection
• ▸WindowManagerService (WMS) - manages every window on screen. Handles window layering (z-order), transitions, insets, and display routing. Works closely with SurfaceFlinger
• ▸PackageManagerService (PMS) - parses APKs, manages installs/uninstalls, resolves Intents to Activities, enforces permissions
• ▸PowerManagerService - controls wake locks, doze mode, screen timeouts, and screen brightness. Apps acquire wake locks to prevent the device from sleeping
• ▸InputManagerService - receives raw input events from the kernel, performs gesture recognition, and dispatches touch/key events to the correct window
• ▸NotificationManagerService - manages the notification shade, ranking, and channels. Enforces Do Not Disturb rules
• ▸AlarmManagerService - schedules delayed or repeating work via AlarmManager API. Wakes up the device at exact times even from deep sleep
• ▸JobSchedulerService - batches background work to minimize battery impact. Enforces constraints (network, charging, idle)

How an App Accesses a Framework Service

  App Code
  val manager = getSystemService(Context.NOTIFICATION_SERVICE)
  manager.notify(id, notification)
       │
       │  looks up 'notification' in ServiceManager
       ▼
  NotificationManager (proxy in app process)
       │
       │  Binder IPC → /dev/binder
       ▼
  NotificationManagerService (in System Server)
       │
       │  validates, ranks, displays
       ▼
  StatusBar Service → shows notification