What is anr?

ANR (Application Not Responding)

An ANR, or Application Not Responding, error occurs when the Android system detects that an application's UI thread has been blocked for too long, making the app unresponsive to user input. This can lead to a frustrating user experience, and Android will prompt the user with a dialog offering them the option to wait or close the application.

There are several reasons why an ANR might occur:

• Performing long-running operations on the main thread: The main thread is responsible for handling UI updates and user input. If a long-running task, like network calls, complex calculations, or database operations, is performed on the main thread, it can block the thread and cause an ANR. To avoid this, use asynchronous tasks like AsyncTask, Threads, Executors, Handlers, or Kotlin coroutines to offload these tasks to background threads.

• Deadlock: Two or more threads can become deadlocked when each thread is waiting for the other to release a resource. This can cause the UI thread to become blocked and trigger an ANR.

• Slow I/O operations: Accessing files or databases on the main thread can be slow and lead to ANRs. Use background threads and proper caching mechanisms to mitigate this.

• Broadcast Receivers: Broadcast Receivers are designed to be quick. If you perform lengthy operations inside a Broadcast%20Receiver's onReceive() method, the application might become unresponsive. Offload the intensive tasks to a background thread or service.

• Excessive garbage collection: While less common, frequent or lengthy Garbage%20Collection pauses can occasionally block the UI thread long enough to trigger an ANR.

To prevent ANRs, follow these best practices:

• Move long-running tasks off the main thread: Use background threads, AsyncTask, IntentService, or other asynchronous mechanisms.
• Avoid performing I/O operations on the main thread.
• Keep BroadcastReceiver onReceive() methods short.
• Optimize code for efficiency.
• Use tools like Android Studio Profiler to identify performance bottlenecks.
• Be mindful of lock contention and potential deadlocks.

When an ANR occurs, Android generates a trace file (typically located in /data/anr/traces.txt) that contains information about the threads and their stack traces at the time of the ANR. Analyzing these traces is crucial for debugging ANR issues. Consider using tools like StrictMode during development to identify potential problems early.