Reporting app hangs

This documentation is for version 2 of the BugSnag Flutter library. We recommend upgrading to the latest release using our Upgrade guide. Documentation for the current release can be found here.

When your app fails to respond to interactions in real time it causes user frustration and can lead them to abandon your app altogether.

iOS only. See ANR detection for Android.

An app hang or freeze is a specific instance of the main thread failing to respond in a reasonable amount of time and can be caused by performing CPU intensive work or performing blocking I/O on the main thread. If your app hangs for 10 seconds or longer, it may be terminated by the system watchdog as described in Apple’s documentation.

BugSnag sends the stack trace of the main thread when an app hang is detected that ends with termination by the system watchdog or being force-quit by the user, helping you to identify the underlying cause. The stack trace will be captured at the point the hang is first detected by BugSnag.

You can also report non-fatal app hangs (i.e. hangs that did not result in the app being killed) by configuring a minimum threshold hang duration.

App hangs are unlikely to occur in Dart code but can happen in native iOS components.

Fatal app hangs

App hangs that end with termination by the system watchdog or being force-quit by the user are considered to be “fatal”. By default BugSnag reports these types of app hangs when a threshold of 2000ms is exceeded.

The system watchdog does not terminate apps launched by Xcode.

Fatal app hangs are sent to your BugSnag dashboard when the app next launches.

Non-fatal app hangs

To enable reporting of non-fatal app hangs, set appHangThresholdMillis to a number of milliseconds. It can be configured to a minimum of 250 milliseconds (0.25 seconds). This threshold applies to both fatal and non-fatal app hangs and is used by BugSnag to prepare an app hang event report when it is exceeded; if the app subsequently recovers from the hang, a non-fatal hang is reported.

void main() => bugsnag.start(
  runApp: () => runApp(const MyFlutterApp()),
  appHangThresholdMillis: 5000,

Disabling detection

BugSnag’s App hang detection can be completely disabled by setting the Enabled Error Types configuration option.

void main() => bugsnag.start(
  runApp: () => runApp(const MyFlutterApp()),
  enabledErrorTypes.appHangs: false,