Cold Start, Warm Start and Hot Start in Android Apps

In the world of mobile app development, creating a seamless user experience is paramount. One of the critical factors that contribute to this experience is how quickly an app starts up and becomes responsive. This process is known as app start-up, and it can be categorized into three phases: Cold Start, Warm Start, and Hot Start.

In this blog, we will delve into each of these start-up phases, explore their implications on user experience, and provide insights into how to improve them.

Android App start scenarios

When you launch an Android app, there are three possible scenarios:

• Cold start: The app is starting from scratch. This is the slowest type of launch, as the system has to create the app's process, load its code and resources, and initialize its components.

• Warm start: The app's process is already running in the background. In this case, the system only needs to bring the app's activity to the foreground. This is faster than a cold start, but it is still slower than a hot start.

• Hot start: The app's activity is already in the foreground. In this case, the system does not need to do anything, as the app is already running. This is the fastest type of launch.

The following sections will discuss each of these types of launch in more detail, and provide tips on how to improve them.

Cold start

A cold start occurs when the app is launched for the first time after installation or after the system has killed the app process. The following are some of the steps involved in a cold start:

1. The system creates the app's process.

2. The system loads the app's code and resources.

3. The system initializes the app's components.

4. The app's main activity is displayed.

The cold start is the slowest type of launch because it involves loading all of the app's code and resources from scratch. This can take a significant amount of time, especially for large apps.

Ideally the app should complete a cold start in 500 milli seconds or less. That could be challenging sometimes, but make sure the app does the cold start in under 5 seconds. There are a number of things you can do to improve the cold start time of your app:

• Use lazy loading: Lazy loading means loading resources only when they are needed. This can help to reduce the amount of time it takes to load the app.

• Use a profiler: A profiler can help you to identify the parts of your app that are taking the most time to load. This can help you to focus your optimization efforts on the most critical areas.

• Use a caching mechanism: A caching mechanism can store frequently used resources in memory, so that they do not have to be loaded from disk each time the app is launched.

• Use a custom launcher: A custom launcher can preload the app's resources in the background before the app is launched. This can significantly reduce the cold start time.

Warm start

A warm start occurs when the app's process is already running in the background. In this case, the system only needs to bring the app's activity to the foreground. This is faster than a cold start, but it is still slower than a hot start.

The following are some of the steps involved in a warm start:

1. The system finds the app's process.

2. The system brings the app's activity to the foreground.

The warm start is faster than a cold start because the app's process is already running. However, the system still needs to bring the app's activity to the foreground, which can take some time.

Ideally the app should complete a warm start in 200 milli seconds or less. In any case, try not to breach the 2 seconds window. There are a number of things you can do to improve the warm start time of your app:

• Use a profiler: A profiler can help you to identify the parts of your app that are taking the most time to bring to the foreground. This can help you to focus your optimization efforts on the most critical areas.

• Use a caching mechanism: A caching mechanism can store frequently used activities in memory, so that they do not have to be recreated each time the app is launched.

• Use a custom launcher: A custom launcher can preload the app's activities in the background before the app is launched. This can significantly reduce the warm start time.

Hot start

A hot start occurs when the app's activity is already in the foreground. In this case, the system does not need to do anything, as the app is already running. This is the fastest type of launch.

There is not much you can do to improve the hot start time of your app, as it is already running. However, you can take steps to prevent the app from being killed by the system, such as using a foreground service or a wake lock. Ideally the app should complete a hot start in 100 milli seconds or less, or in a worst case scenario, under 1.5 seconds.

Conclusion

The cold start, warm start, and hot start are the three different types of app launches in Android. The cold start is the slowest type of launch, while the hot start is the fastest.

There are a number of things you can do to improve the launch time of your app, such as using lazy loading, caching, and a custom launcher.

I hope this blog post has been helpful. If you have any questions, please feel free to leave a comment below.