Understanding ConcurrentModificationException in Android SDK: Causes and Solutions

Dive into how to track down the causes of `ConcurrentModificationException` in your Android applications, particularly when dealing with network calls. Learn best practices to avoid this issue in your development workflow.
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Tracking Down ConcurrentModificationException After a Network Call

Developing Android applications, especially SDKs that interact with APIs, can often lead to frustrating issues. One common error developers encounter is ConcurrentModificationException. If you've ever found yourself puzzled by this exception, particularly when it seems that no code modification is occurring at that moment, you're not alone. This post delves into the root cause of this issue by analyzing a specific scenario and offering practical solutions.

The Problem Scenario

You’ve created an Android SDK and have received reports about ConcurrentModificationExceptions. However, replicating this exception on your device proves to be a challenge. In the logcat output, we can see relevant activity related to a CameraViewModel receiving a response from an API, followed closely by the exception. This may signal that the list is being altered while it is being traversed, a common situation leading to this error.

Log Review

The logcat indicates:

A response from an API call is received (CameraViewModel: response here:).

Shortly thereafter, a ConcurrentModificationException is thrown.

The Exception points to a method involving list iteration, where an ArrayList is being modified.

Code Snippet

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And in the function getResponse which appears to be responsible for processing the response, we have:

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Analyzing the Cause

Non-reproducibility: The sporadic nature of this exception arises from the fact that it’s dependent on timing; the condition might not always trigger if processes don’t overlap.

Solutions to Avoid ConcurrentModificationException

To mitigate this type of exception, consider these approaches:

1. Pass a Copy of the List

Instead of directly passing entries, which could be modified, create a copy of it when making the API call:

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This ensures that you can manipulate copiedEntries without affecting the original entries that other processes might still be using.

2. Synchronize Access

If sharing the entries list across multiple threads is necessary, consider using synchronization:

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This approach ensures that the critical section is accessed mutually exclusively by one thread at a time.

3. Use Thread-Safe Collections

Consider leveraging thread-safe collections like CopyOnWriteArrayList which are specifically designed to handle concurrent modifications without throwing exceptions.

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This can significantly reduce the likelihood of encountering ConcurrentModificationException during possible modifications.

Conclusion

The ConcurrentModificationException in Android can be a headache for developers, but understanding the nature of your data structures and how they are managed across different threads can go a long way toward preventing errors. By adopting safer coding practices such as passing copies of lists, synchronizing access to shared resources, or op