Ending all threads started by dialog on dialog close/end

[r0n]

In a running QM dialog called "testdialog" I have a button that starts the functions: "StartTestFunction_1" and "StartTestFunction_2"
If I close the dialog "testdialog" I want to close ALL the separate threads started by it. (meaning close/end: "StartTestFunction_1" and "StartTestFunction_2")

I have 2 questions

1) How I do it. Is this correct?  (It works but I need to know if this is correct approach)

Code:

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    case WM_CLOSE
        shutdown -6 0 "StartTestFunction_1"
        shutdown -6 0 "StartTestFunction_2"
    case WM_DESTROY
        shutdown -6 0 "StartTestFunction_1"
        shutdown -6 0 "StartTestFunction_2"

2) Is there a more effective (shorter) way to end ALL threads started through a QM dialog? (must also work in .exe)