How to Diagnose an ANR or Freeze That Produces No Crash on Android

An ANR is not a crash, so the usual crash tooling shows nothing and you are left with a frozen screen and an angry dialog. Android does record exactly what the main thread was doing when it froze, though, in a trace file you have to go and get.

How to diagnose it

1. Capture the ANR trace

Pull /data/anr/traces.txt (or use adb bugreport) right after the freeze. It contains a thread dump captured at the moment the system decided the app was unresponsive.

2. Find the main thread stack

Locate the main thread in the dump. Its top frames show exactly what call was running when the watchdog fired, which is the work blocking your UI.

3. Identify the blocking operation

ANRs almost always come from synchronous file or network I/O, a giant loop, or a lock the main thread is waiting on. Confirm which by what the stack is sitting in.

4. Move the work off the main thread

Push I/O and heavy computation to a background thread or coroutine and post only the result back to the main thread. Keeping the main thread free of long calls eliminates the ANR.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every mobile error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.