tell me comprehensive info about hangs and how to detect them, solve them and what are they

Hangs in applications typically refer to situations where the app becomes unresponsive, often due to excessive CPU usage or blocking operations on the main thread. Detecting and solving hangs involves using various tools and techniques to identify the root cause and optimize the code.

Detecting Hangs

1. Instruments in Xcode:

   • Use the specialized Hangs instrument to analyze blocking behaviors between threads and identify issues impacting the UI or the app's main thread.
   • The System Trace instrument can help analyze thread interactions and identify which threads are blocking others.

2. Thread Performance Checker:

   • This tool in Xcode helps identify main thread hangs and priority inversions. It can also show excessive disk write and slow app launch diagnostics, which are often related to hangs.

3. Flame Graphs:

   • Available in Instruments, flame graphs provide a high-level overview of CPU usage and can help identify long hangs during app launch or execution.

Solving Hangs

1. Algorithm and Data Structure Optimization:

   • If hangs are due to inefficient algorithms, consider changing the algorithm or its implementation to improve efficiency.

2. Avoiding Main Thread Blockages:

   • Ensure that heavy operations, such as loading assets or performing complex calculations, are not executed on the main thread.

3. Using Breakpoints and Debugging Tools:

   • Set breakpoints to inspect the state of the program and identify the exact line of code causing the hang. Use the unified backtrace view in Xcode to trace the call stack and understand the flow of execution.

4. Analyzing CPU Usage:

   • Use Xcode's built-in CPU gauge to detect if CPUs are heavily used while interacting with your app. This can indicate areas where optimization is needed.

Understanding Hangs

Hangs occur when the app's main thread is blocked, preventing it from processing user interactions or updating the UI. This can be due to:

• Excessive CPU Usage: When the CPU is overwhelmed with tasks, it can lead to hangs.
• Blocking Operations: Operations that wait for resources or perform long computations on the main thread can cause the app to hang.

For more detailed guidance on optimizing CPU performance and analyzing hangs, refer to the session Optimize CPU performance with Instruments (00:03:26).