For the past decade, AysncTask has been one of the most widely used solutions for writing concurrent code in Android. However, it earned very controversial reputation. On the one hand, AsyncTask powered, and still powers, many Android applications. On the other hand, most professional Android developers openly dislike this API.
All in all, I’d say that Android community has love-hate relationship with AsyncTask. But there are big news: the era of AsyncTask is about to end because a commit that deprecated it had just landed in Android Open Source Project.
In this post I’ll review the official statement motivating AsyncTask’s deprecation, as well as the real reasons why it had to be deprecated. As you’ll see, these are different sets of reasons. In addition, towards the end of this article, I’ll share my thoughts on the future of Android’s concurrency APIs.
Official Reason for Deprecation of AsyncTask
The official deprecation of AsyncTask, as well as the motivation for that decision, were introduced with this commit. The newly added first paragraph of Javadoc states:
AsyncTask was intended to enable proper and easy use of the UI thread. However, the most common use case was for integrating into UI, and that would cause Context leaks, missed callbacks, or crashes on configuration changes. It also has inconsistent behavior on different versions of the platform, swallows exceptions from
doInBackground, and does not provide much utility over usingExecutors directly.
While that’s the official statement by Google, there are several inaccuracies there which are worth pointing out.
Fist of all, AsyncTask has never been intended to “enable proper and easy use of the UI thread”. It was intended to offload long-running operations from UI thread to background threads, and then deliver the results of these operations back to UI thread. I know, I’m nitpicking here. However, in my opinion, when Google deprecates API that they themselves invented and promoted for years, it would be more respectful towards developers who use this API today, and will continue to use for years to come, to invest more effort into deprecation message to prevent further confusion.
That said, the more interesting part of this deprecation message is this: “that would cause Context leaks, missed callbacks, or crashes on configuration changes”. So, Google basically states that the most common use case for AsyncTask automatically results in very serious problems. However, there are many high-quality applications out there which use AsyncTask and work flawlessly. Even some classes inside AOSP itself use AsyncTask. How comes they don’t experience these problems?
To answer this question, let’s discuss the relationship between AsyncTask and memory leaks in details.