Processes and threads in Android

Jul 17, 2024

1. Processes:

By default, each component of an android app is run in the same process.

But, we can change that so different components can run in separate processes —> This is done by modifying the manifest file.

2. Threads:

When an application is launched, the system creates a thread of execution called main thread.

The main thread will deal with stuff like user interface, drawing events,.. so it can be called UI thread.

If we run everything on the main thread, sometimes it can yield a poor performance when handling tasks such as network access, images loading, DB queries,… —> Any of these tasks can block the main thread and cause lagging or even the “Application Not Responding” error.

The Android UI toolkit is not thread-safe, then don’t use something related to the UI on the worker thread.

There are 2 rules:

  • Don’t block the UI thread
  • Don’t access the Android UI toolkit from outside the UI thread

Android offers several ways to access the UI thread from other threads:

  • Activity.runOnUiThread(Runnable)
  • View.post(Runnable)
  • View.postDelayed(Runnable, long)

Ex: we load the image in the worker thread but only update it on the UI in the UI thread only.

fun onClick(v: View) {
    Thread(Runnable {
        // A potentially time consuming task.
        val bitmap = processBitMap("image.png")
        imageView.post {
            imageView.setImageBitmap(bitmap)
        }
    }).start()
}

Refs:

https://developer.android.com/guide/components/processes-and-threads#kotlin