I'm calling a suitelet from another system, the suitelet immediately returns a response

context.response.write('File Received');

and then proceeds to do quite a lot of processing. It seems that the external system is only get the response after the suitelet has finished all its processing rather than at the response.write, this is causing the external system to get timeout issues as the request seems to take a long time, does anyone know how to immediately have the suitelet return a response and then continue processing?