yield from interrupt

[morgoth990]

I'm trying to limit the execution time calling lua_yield() from the interrupt callback but seems to trigger an exception.
It's possible to yield from the interrupt callback or how can I achieve the same result?

[morgoth990]

browsing the sources the only way I see is to set lua_singlestep() to true before lua_resume() and call lua_yield() from the debugstep callback

[zeux]

Yields don't really work in interrupts (in general interrupts are very special and permit almost no interaction with the VM). The only thing that works atm is raising an error. I think to enable yields you'd need to edit VM_INTERRUPT macro in lvmexecute.cpp, I'd guess it would be like this but I haven't tested it:

#define VM_INTERRUPT() \
    { \
        void (*interrupt)(lua_State*, int) = L->global->cb.interrupt; \
        if (LUAU_UNLIKELY(!!interrupt)) \
        { /* the interrupt hook is called right before we advance pc */ \
            VM_PROTECT(L->ci->savedpc++; interrupt(L, -1)); \
            if (L->state != 0) \
            { \
                L->ci->savedpc--; \
                goto exit; \
            } \
        } \
    }

Note that interrupt callback will also be called from GC where it's unsafe to error or yield, so you'd need to check the input argument before making this decision.

[morgoth990]

It's working.
Any chance to have this on the main repo to mantain compability? Shouldn't have a noticeable impact on performance.

[zeux]

I'll take a look at this, I've created #287 so that this doesn't get lost.