According to the Android docs:

A service runs in the main thread of its hosting process;

Does this mean that, even if I have another thread running and I start the service from that thread, it still will run on the UI/Main thread?

For example, I have a React-Native application, and I use a native module to start a foreground service. In React-Native Native native modules run on a separate thread - so will the service here run on the native module's thread or will it still run on the main thread?

CodePudding user response：

Yes, that's correct. The Android system will always run a foreground service on the main thread of the hosting process, even if you start the service from a background thread. This is to ensure that the foreground service runs smoothly and can interact with other parts of the system, such as the notification system, without any problems. If the work performed by the foreground service is long-running or resource-intensive, it's recommended to use a separate worker thread to perform the work and keep the main thread free for other tasks.

In React Native, starting a foreground service using a native module would run on the native module's thread, which is separate from the main thread. However, once the service is started, it will run in the main thread of the hosting process as specified by the Android system.

So, while the native module may start the service on its own thread, the service itself will run on the main thread and have access to the Android API, as well as be subject to the same restrictions as any other foreground service. If the work performed by the service is long-running or resource-intensive, it's recommended to use a separate worker thread to perform the work and keep the main thread free for other tasks.