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Fixing 'Xcode build failed due to concurrent builds' in Flutter

Flutter, Xcode, Troubleshooting2 min read

Encountering the "Xcode build failed due to concurrent builds" error in Flutter can disrupt your development flow. It signifies that another process is already using the build folder or intermediate files, preventing a clean build. Fear not, for there are ways to reclaim control! This article equips you with methods to identify and eliminate the conflicting process, using commands readily available in your terminal.

Understanding the Culprit

This error surfaces when Xcode attempts to build your Flutter app but detects the build folder or temporary files locked by another process. This could be a previous build that didn't complete cleanly or another instance of Flutter running in the background.

Finding the Offender

  1. Open Terminal: Fire up your terminal application.

  2. Identify the Process ID (PID): Here's where we hunt down the culprit. We can utilize two methods:

    • Method 1: Using ps aux | grep xcodebuild

      This command displays a comprehensive list of running processes, with "grep xcodebuild" filtering the results to processes containing "xcodebuild." Look for entries related to Xcode builds, particularly those in the "DEVEL" state.

    • Method 2: Using top -o command

      This approach employs the top command to display a dynamic view of running processes. The -o command argument lets you sort the list based on a specific column. Here, we'll use %CPU to sort by CPU usage. Locate processes related to Xcode builds and identify the one consuming a significant amount of CPU.

  3. Note the Process ID (PID): Regardless of the method used, make sure you capture the PID (Process ID) of the process you suspect is causing the conflict.

Taking Down the Intruder (Use with Caution!)

  1. Terminate the Conflicting Process: Now that you have the PID, use the kill -9 command to forcefully terminate the process. However, exercise caution:

    1kill -9 <PID>

    Remember, kill -9 is a forceful termination method that could lead to data loss in unsaved work. Double-check the PID before proceeding to ensure you're targeting the correct process.

  2. Rebuild with Confidence: After eliminating the conflicting process, return to your development environment and confidently attempt to build your Flutter app again using flutter run or your preferred method. If it's still not working try running flutter clean and then flutter run again.

Bonus Tips

  • Background Process Check: Before resorting to kill -9, verify you haven't left any lingering instances of Flutter or Xcode in the background. Close any development tools or terminals that might be holding onto the build folder.
  • Clean Build Alternative: Consider employing flutter clean before your next build attempt. This command removes leftover build artifacts, potentially resolving the conflict without forceful termination.

By following these steps and wielding the power of your terminal commands, you should be able to effectively neutralize the "Xcode build failed due to concurrent builds" error and resume your Flutter development seamlessly. Remember to exercise caution when using kill -9.