wakelock

A wakelock is a mechanism used by operating systems and applications to keep a device from entering a low-power sleep state. By acquiring a wakelock, an app or the system can request that certain components, such as the CPU or the display, remain awake to complete a task. Wakelocks are most commonly discussed in the context of Android, where they are exposed as an API that allows apps to prevent the CPU from sleeping while work is being done in the background.

In Android, a wakelock is managed through the PowerManager class. An app can acquire a wakelock to keep the CPU running, even if the screen is off, and later release it when work is finished. There are different levels and flags, such as partial wake locks that keep the CPU on but allow the screen to turn off, and full or screen-related locks that keep the display on. Some flags, like ACQUIRE_CAUSES_WAKEUP, can also wake the device when the lock is acquired. Modern Android guidance emphasizes using wake locks sparingly and with proper lifecycle management, often favoring alternative scheduling mechanisms when possible.

Misuse or failure to release wakelocks can lead to unnecessary battery drain and degraded performance. Developers monitor wakelock behavior with tools such as adb dumpsys power and Battery Historian, aiming to minimize wake time. Best practices include acquiring wakelocks only for the minimum duration needed, using timeouts to prevent leaks, and preferring scheduled work via WorkManager, JobScheduler, or AlarmManager over continuous wakefulness.

Wakelocks originate from the Linux-based kernel’s power management and represent a key mechanism for controlling sleep, with Android providing a higher-level API to manage device wakefulness.