C++ stop other programs by PID on brute force quit from client

Question

I have an .exe Program, which triggers some other files during execution.

So at a given point, the tree might become like:

Main program
    -Program 1
    -Program 2
    -Program 3

Of all these programs I have their PID, so I am able to close them successfully. However, when a user 'brute forces the program' (read close the program manually), I am unable to close these child programs. Is there an option to trigger the closing of child-programs before the main-program itself will actually exit. (Something is for example also possible in an html-page to remind the user e.g. or they really want to leave te page).

Because, when this situation occurs, on the next run the main-program will try to start up these child-programs again, however they are already running. (And the settings of the main-program are time dependent and have to be transferred to the other child-programs on start-up to work properly)

Ideally, I would like to have a cross-platform solution, since I have to make the app available for Windows, Linux and MacOS.

Thanks for your answers.

Answer 1

This is an OS feature and each OS offers it in its own way. Keeping track of the PIDs does not work, for once for the reason you mention (your parent process may itself crash) and second because the child process may spawn grand-children processes of its own that needs to be tracked, and then grand-grand-children and so on.

On Windows this is handled by NT Job Objects by asking for the JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE:

Causes all processes associated with the job to terminate when the last handle to the job is closed.

The way to use it is to create the job object in the parent process and make the handle non-inheritable. Then any child process will become part of the job, but only one handle exisst (the one owned by the parent). If the parent crashes then the handle is reclaimed by the OS and this will terminate the NT job object, killing all child processes as well as any grand-child or grand-grand-child process.

On Linux (and OS X) the same functionality is achieved with process groups.

I am not aware of any cross-platform library that would abstract this into a coherent uniform API.