# System Hang Constants Use one or more of the following constants in the parameter of [`setExceptionHangingMask(_:)`](/documentation/ExceptionHandling/NSExceptionHandler/setExceptionHangingMask(_:)) to specify the types of exceptions that cause the exception to halt execution so a debugger can be attached. ## Overview When exception-handling domains are nested, [`NSHangOnTopLevelExceptionMask`](/documentation/ExceptionHandling/NSHangOnTopLevelExceptionMask) deals with exceptions that would make it to the top two levels of exception handlers. In the main thread of a Cocoa application, the top-level handler is the global instance. ## Topics ### Constants [`NSHangOnUncaughtExceptionMask`](/documentation/ExceptionHandling/NSHangOnUncaughtExceptionMask) The exception handler suspends execution when it detects an uncaught exception (other than a system exception or runtime error). [`NSHangOnUncaughtSystemExceptionMask`](/documentation/ExceptionHandling/NSHangOnUncaughtSystemExceptionMask) The exception handler suspends execution when it detects an uncaught system exception. [`NSHangOnUncaughtRuntimeErrorMask`](/documentation/ExceptionHandling/NSHangOnUncaughtRuntimeErrorMask) The exception handler suspends execution when it detects an uncaught runtime error. [`NSHangOnTopLevelExceptionMask`](/documentation/ExceptionHandling/NSHangOnTopLevelExceptionMask) The exception handler suspends execution when it detects an exception that would be handled by the top-level handler. [`NSHangOnOtherExceptionMask`](/documentation/ExceptionHandling/NSHangOnOtherExceptionMask) The exception handler suspends execution when it detects an exception that would be handled by an object other than the top-level handler. ### Containing Objective-C enumeration --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)