How to fix “The thread is not in background processing mode. [ERROR_THREAD_MODE_NOT_BACKGROUND (0x191)]” – Error Code 401

Overview

In this article, we’ll focus on resolving the issue described as: “The thread is not in background processing mode. [ERROR_THREAD_MODE_NOT_BACKGROUND (0x191)]”. This error, identified by the error code Error Code 401, can impede your system’s performance, and here’s how you can fix it.

Identifying the Problem

Error Code 401 occurs when a thread attempts to perform an operation that is not allowed in background processing mode. This error typically arises in multithreaded applications where threads are executing in both foreground and background modes.

Common Fixes

• Check thread priority: Ensure that the thread experiencing the error is not set to a higher priority than the foreground thread.
• Use BeginThread instead of CreateThread: When creating background threads, use the BeginThread function instead of CreateThread. BeginThread automatically sets the thread priority to BACKGROUND_PRIORITY_CLASS.
• Set thread priority in CreateThread: If using CreateThread, explicitly set the thread priority to BACKGROUND_PRIORITY_CLASS using the SetThreadPriority function.

Advanced Troubleshooting

• Debug the application: Use debugging tools like Visual Studio or WinDbg to identify the source of the error and determine which thread is triggering it.
• Check for thread synchronization issues: Ensure that threads are synchronized correctly using synchronization primitives like mutexes and events.
• Consider using a thread pool: Thread pools can help manage thread priorities and ensure that background threads are not starved of resources.

Conclusion

Error Code 401 can be resolved by ensuring that threads are created and executed in the appropriate background processing mode. By following the fixes and troubleshooting steps outlined in this article, you can address this error effectively and prevent it from recurring in the future. Remember to maintain proper thread management practices to ensure optimal system performance.