How is application priority determined in the system?

The priority of an application in Android is determined based on several factors, the main ones being:

• Component activity: An application with active components (activities in the foreground, services started with startForeground) has a higher priority.
• Resource usage: Applications actively using CPU or occupying a lot of memory may be marked by the system as lower priority to conserve resources for more important tasks.
• User interface interaction: Applications that directly interact with the user at the moment receive the highest priority.
• Connection with higher priority processes: A process associated with a component (for example, a service connected to an activity) inherits the priority of a higher process.

The Android system uses these factors to determine the "importance level" of an application, which ultimately decides how likely its process is to be terminated (killed) when resources are scarce.

Main process importance levels:

• Foreground process: The most important process. An application with a visible activity, a service started with startForeground, or using certain APIs (for example, related to another foreground activity). It is never terminated by the system unless critical resources are exhausted.
• Visible process: A process that does not have components in the foreground but affects what the user sees. For example, a process containing a service related to a foreground activity.
• Service process: A process containing a service started with startService and not marked as a foreground service. It can be terminated when memory shortage becomes serious.
• Cached process: A process that does not contain active components and is kept in memory for faster resumption of work. The least important process and the most likely candidate for termination when memory is scarce.