Addressing native memory leaks in React native applications

At some point, most React developers will have to deal with the headache of managing a memory leak. Memory leaks could destroy your project or, at the very least, delay it - all while costing you unnecessary stress and time. Whenever a leak happens, slowdowns, crashes, high latency, and other issues are sure to follow.

Here are some tips to help you identify memory leaks and fix them at the source as quickly and economically as possible.

Identifying a leak

A memory leak happens when a certain amount of memory that is no longer required by an application does not get returned to the pool of available memory. The problem is that returning bits of unused memory to the operating system is an undecidable problem. That is, it can’t happen automatically. It is up to developers to specify whether any piece of memory is to be returned. Unfortunately, it is very easy to overlook this, especially if several developers work together.

Another problem is that it is tough to tell if a leak has occurred. They’re often so small that you wouldn’t even notice, and then you must back and carefully analyze your work if performance starts to suffer.

To identify the leak, go back to your app and analyze a particular workflow that you would expect to be memory-neutral - something like moving back and forth between screens, for example. If there is a leak, you will see your app’s memory consumption increase as you perform these functions. The best way to run this test is through Instruments (if you are working in iOS) or Studio Profiler in Android.

What to do when you find a memory leak

Once you have run your analysis and you notice that memory usage is definitely increasing inordinately, the next question to ask is whether the problem you are seeing is definitely a memory leak. When working in iOS, you can use the Apple XCode Reprofiling tool to profile it - this should give you a definitive answer. If it is a leak, it can affect the app’s performance and even end up crashing the system, so you need to come up with a fix for it as quickly as possible.

When searching for an effective solution, it is important to understand what is actually happening in your app. The best way to explain this is in terms of memory subscriptions. These are created whenever a component is mounted. If they are not unsubscribed when that component is unmounted, that’s when a memory leak occurs. You need to remove those subscriptions when the component unmounts. Once you have identified the component in question, there are a few solutions you could apply:

1. Use AbortController

With this interface in Javascript, you can abort one or more Web requests as required. You can use AbortController to cancel the request that is causing the problem, and this should clear up the leak.

2. Clear intervals

The setInterval function could be the source of your problem. If you have set up any repeating tasks to recur every second or so, this can often result in a memory leak - it will need to be cleared after unmounting.

3. useStateifMounted hook

This hook is similar to useState, but it adds a vital criterion: it stipulates that the state of your component should be updated only if it is mounted. If it is not mounted, it will not be updated, and the allocated memory will be released.

4. useEffect hook

By simply adding ‘isMounted’ to your useEffect hook, you can ensure that data will not be retrieved if the component is unmounted. That way, the data can be saved.

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