Limiting execution time

[morgoth990]

My plan is to limit the execution time to avoid to lock the game thread.
I have managed to succesfully break the execution using debugstep, the idea is to set debugstep=nullptr, call lua_resume and use a parallel thread to set debugstep = DebugStep_TIMEOUT_YIELD when the timeout is expired.

void CPU::DebugStep_TIMEOUT_YIELD(lua_State* L, lua_Debug* ar)
{
	if (lua_isyieldable(L))
		lua_yield(L, 0);
}

Using this method debugstep doesn't affect the performance.

The questions are:

• Is this ok or there's a better way?
• It's ok to change debugstep from a different thread?
• If so, should debugstep be tagged volatile?

[JDaance]

From lua.h, line 345 or so

/* Callbacks that can be used to reconfigure behavior of the VM dynamically.
 * These are shared between all coroutines.
 *
 * Note: interrupt is safe to set from an arbitrary thread but all other callbacks
 * can only be changed when the VM is not running any code */
struct lua_Callbacks
{
    void* userdata; /* arbitrary userdata pointer that is never overwritten by Luau */

    void (*interrupt)(lua_State* L, int gc);  /* gets called at safepoints (loop back edges, call/ret, gc) if set */
    void (*panic)(lua_State* L, int errcode); /* gets called when an unprotected error is raised (if longjmp is used) */

    void (*userthread)(lua_State* LP, lua_State* L); /* gets called when L is created (LP == parent) or destroyed (LP == NULL) */
    int16_t (*useratom)(const char* s, size_t l);    /* gets called when a string is created; returned atom can be retrieved via tostringatom */

    void (*debugbreak)(lua_State* L, lua_Debug* ar);     /* gets called when BREAK instruction is encountered */
    void (*debugstep)(lua_State* L, lua_Debug* ar);      /* gets called after each instruction in single step mode */
    void (*debuginterrupt)(lua_State* L, lua_Debug* ar); /* gets called when thread execution is interrupted by break in another thread */
    void (*debugprotectederror)(lua_State* L);           /* gets called when protected call results in an error */
};
typedef struct lua_Callbacks lua_Callbacks;

I don't know the intricacies of this, but I noticed this comment recently which seems relevant to your case! Using interrupt may be exactly what you need?

[morgoth990]

I have tested it, interrupt can't call lua_yield/break.
The only way to use interrupt is the solution suggested in this discussion #208