Part of a build engineer’s role is to speed up builds. Improving build performance and avoiding work with caching is one way to achieve this, but another tool in the build engineer’s belt is that of disallowing slow builds. This is part two in a series about solving Gradle remote build cache misses.
Until recently, one of the top technical risks facing SoundCloud’s Android team was increasing build times. Our engineering leadership was well aware of the problem, and it was highlighted in our company’s quarterly goals and objectives as modularization. Faster build times means more productive developers. More productive developers are happier and can iterate on products more quickly.
Modularization is key to decreasing build times, but avoiding work is another important part of the puzzle, and build caching is one way to avoid that work. Gradle, our tool for building Android, has a local file system cache that reuses outputs of previously performed tasks. We have been using the Gradle remote build cache in order to save our developers’ time. It helps us avoid redoing work that other teammates have already done or switching to old branches. However, to get the full benefits of caching, you have to go beyond simply setting it up.
Media and playback are at the core of SoundCloud’s experience. For that reason, we have established and grown an engineering team that is specialized in providing the best possible streaming experience to our users across multiple platforms.
To do this, we combine the industry’s best-fitting solutions with our own custom technologies, libraries, and tools. In this article, let’s dive into how we improved latency in our Android application by leveraging a new engine for our player’s audio sink.
Once every two weeks, we prepare new versions of our mobile apps to be published to the app stores. Being confident about releasing software at that scale — with as many features and code contributions as we have and while targeting a wide range of devices like we do at SoundCloud — is no easy task. So, over the last few years, we have introduced many tools and practices in our release process to aid us.
In this blog post, I’ll cover some of the techniques we use to guarantee we’re always releasing quality Android applications at SoundCloud.
Testing mobile applications is not always an easy feat. In addition to defining what to test and determining how to write those tests, actually running tests can also be problematic — in particular, UI test suites running on real mobile devices or emulators sometimes run for an extensive amount of time.
Last week, we open-sourced LightCycle, an Android library that helps break logic out of
Fragment classes into small, self-contained components called LightCycles.
Components that typically need to be aware of
Fragment lifecycle events include presenters, UI tracking code, input processors and more. We’ve been using LightCycle extensively in the SoundCloud Music & Audio and SoundCloud Pulse apps over the last year.
In part one we described how running into Android’s method limit may leave you unable to build, and offered strategies you can employ to make your app fit into a single DEX file. In this part we share an alternative option: using multiple DEX files.
At SoundCloud we have been building for the Android platform since 2010. Much has changed since then: the team has grown, the list of features has grown, and our audience has grown. Today, eight engineers are working full time on the official SoundCloud app, across various areas, with contributions pouring in from other parts of the organization. Due to the growing complexity and number of contributions, the app’s size has grown substantially. Currently the app consists of approximately 1200 Java source files, not counting tests, containing approximately 86000 lines of code. This doesn’t include native code, such as our playback or recording stacks.
We’re not the first to run into Android’s limits in terms of build tools. An internal limitation of Dalvik’s byte code format (DEX), which I will explain in more detail, can leave you unable to build after your codebase reaches a certain size. If you fail to anticipate this, it might happen during the most inconvenient time, such as when you are preparing for a release. Part of our job in Core Engineering at SoundCloud is to make sure our developers are happy and productive; not being able to build our app anymore makes for neither happy nor productive developers.
While there are a number of posts on this topic, I would like to describe in more detail what we have done to combat Android’s method limit, what things worked well and what didn’t work so well, what it actually means to use the
--multi-dex switch and what you can do to improve application health with regards to size.
Both our Android and iOS teams use the reactive programming paradigm to simplify asynchronous, concurrent code in our native mobile apps. For Android, we use Netflix’s RxJava. Matthias Käppler—a SoundCloud engineer and a contributor to the RxJava Android library—blogs about the HOWs and WHYs of RxJava on Android.
A common problem in Android development is that you need to jump off the main UI thread to retrieve data from an IO-based source. At SoundCloud, we use Netflix’s RxJava to simplify asynchronous flows in Android. In an interview given for the Google Developers series “root access Berlin”, Mustafa Sezgin—who heads up our Mobile Team—explains why we chose RxJava, what it gives us, and he walks…