Interrupting computations using signals

[Daniel Mendler]

If Emacs is running in GUI mode, I can interrupt computations by
pressing `C-g` (keyboard-quit). Is there also a possibility to submit
such an interrupt from outside, via signals or via another mechanism?

This feature would be useful when running computations in an external
Emacs worker process. Ideally there is some API which allows to enable
external interrupts only within an interruptible section. Note that I
can always terminate a worker process via the OS mechanisms, but that is
not the point here, I want to make it interruptible instead.

I've read something in the manual about SIGUSR1/SIGUSR2 but I could not
get these handlers to work in an Emacs running in daemon or batch mode.

Daniel