Understanding Crashes and Crash Logs

WWDC 2018

Crashes Organizer

Xcode → Window → Organizer (Shift + Command + 6)

Device Window

You can get logs from a device.

Automated testing

Symbolication

• Upload app symbols for server-side symbolication
• Keep your app archive for local symbolication
• Download debug symbols for bitcode apps

Analyzing Crash Logs

Assertions and Preconditions

• Forced unwrap of an Optional that stores nil
• Out of bounds Array access
• Swift arithmetic overflow
• Uncaught exception
• Custom assertion in your code

Terminations by the Operating System

• Watchdog events (time out)
• Device overheated
• Memory exhaustion
• Invalid code signature

Avoiding Launch Timeouts

• Test your app without the debugger
• Test your app on a real device
• Test your app on older hardware

Memory Errors

Object life cycle

Dealloc → Freed object → Rotate

Crash Log Analysis

• Understand the crash reason
• Examine the crashed thread’s stack trace
• Look for more clues in bad address and disassembly 👍

Common Memory Error Symptoms

Crash Analysis Tips

• Look at code other than the line that crashed
• Look at thread stack traces other than the crashed thread
• Look at more than one crash log
• Use Address Sanitizer and Zombies to reproduce memory errors

Multithreading Issues

Use theThread Sanitizer to fix multi-threading issues

Demo

Tips

Use the thread name