I see this https://issues.apache.org/jira/browse/NIFI-78 on jira but it's referencing java. Is there a way to map the nifi process with a thread on the server so I can manually kill it?
There short answer is... no there is not a way to force kill a stuck processor, you would have to restart the NiFi server.
Longer explanation...
The NiFi application is a single Java process and this process then uses Java threads to concurrently execute the processors.
If the code in a processor gets stuck doing something, then the thread that was executing the processor is stuck, which is usually when you see a persistent number in the top-right corner of a processor.
The most common case of a processor getting stuck is when it uses a client library to make a connection to an external system, and the system is not responding and the client library does not provider good configurable timeout properties, or it does but the processor did not set them.
If this is a processor provided by Apache NiFi then we can file a bug and try to improve the processor to avoid these situations.
If it is a custom processor then it is up to the developer to follow best practices to avoid these conditions.