Understanding Xcode’s Leaks Instrument

Xcode’s Leaks Instrument is a powerful tool for detecting memory leaks in your app. It allows you to gather information about leaked memory, including the address, size, and type of data, as well as its contents. However, it appears that the “Gather leaked memory contents” feature sometimes produces an unexpected result.

Symptoms of Incorrect Leaks Instrument Output

When running the “Gather leaked memory contents” feature in Xcode’s Leaks Instrument, you might notice that instead of displaying the ASCII string beside each hex dump, it only shows the hex contents. This is particularly frustrating because it makes the content un-selectable and impossible to copy into a decent hex editor for further analysis.

Alternative Approach: Running Leaks from the Command Line

Fortunately, there’s an alternative approach to achieve your desired output. You can run leaks from the command line, which allows you to gather information about leaked memory in a more detailed format. Here’s how to do it:

Finding the Process Name of Your Running App

First, you need to find the process name of your running app. You can use tools like Activity Monitor or top to achieve this.

• Activity Monitor: To use Activity Monitor, follow these steps:

  1. Open Activity Monitor on your Mac.
  2. In the left-hand sidebar, select “Process” under the category labeled with a process name that matches your app’s name.
  3. Once you’ve found your app’s process in the list, take note of its name.

  top command: If you’re on a Mac running an older version of macOS (pre-Catalina), you might need to use the top command instead. Here’s how:

  1. Open Terminal.
  2. Run the following command: ps -eo pid,cmd
  3. Look for your app’s process ID and command name in the output.

Running Leaks from the Command Line

Once you have your app’s process name, run the leaks command to gather information about leaked memory:

# Run leaks on your app
leaks <app_name>

Replace <app_name> with the actual name of your running app. The output will display various details, including the address, size, and type of data, as well as its contents if possible.

Benefits of Running Leaks from the Command Line

Running leaks from the command line has several benefits over using Xcode’s Leaks Instrument:

• More detailed output: The command-line version provides a more comprehensive view of leaked memory, including ASCII string contents.
• Customization: You can use various options to customize the output and tailor it to your needs.

Available Options for Leaks

The following are some common options available when running leaks from the command line:

# Common options for leaks:
- -p, --pid <pid>  PID of the process to inspect
- -s, --size      Show only sizes greater than the specified value
- -t, --type      Show only types matching the specified value

For example, you can use these options to find memory blocks larger than 1024 bytes or with a type that matches char:

# Find memory blocks larger than 1024 bytes and of char type:
leaks -s 1024 -t char <app_name>

Conclusion

While Xcode’s Leaks Instrument can be an effective tool for detecting memory leaks, its “Gather leaked memory contents” feature may not always provide the desired output. Fortunately, running leaks from the command line offers a more detailed and customizable approach to gathering information about leaked memory. By following these steps, you should be able to obtain the ASCII string contents of your app’s leaked memory blocks for further analysis.

Last modified on 2025-03-29