>>>>I created a small executable to run a process in the background, so the application does not hang while the process is executed. A timer then checks for the file created and shows the result. I did not use ParallelFox, because I did not want to register any additional libraries at the clients, but not sure if I can succeed.
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>>>>Because there is one small problem: When starting the process (using api_Apprun with "HID") the main application loses its focus for a short time. That can be annoying when you are typing or doing anything, and then for a split second the focus goes away, and that every few minutes. So I wonder if there is a way to run the process without losing focus of the calling application, or if there is a way to use ParallelFox without registering, or perhaps another idea?
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>>>You can run the process as a service. Or like I used to do, run it on a server or a separate machine. All "communication" with the process is done by sending a file with "instructions", and the process responds by creating a file with the "answers".
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>>Yes that could be an idea. So the process stays active in the background and waits for instructions. Only problem, it needs to quit when I close the main application. Of course it was easier to create it in such a way to start it with a parameter, run the process, and then quit, but your solution might be the next best thing and solves the original issue.
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>One of the instructions sent via the file, can be to shut itself down.

You are a genius !