Function lua_gc

third-party/lua-5.5.0/src/lapi.c:1170–1243

** Garbage-collection function */

** Garbage-collection function
*/
LUA_API int lua_gc (lua_State *L, int what, ...) {
  va_list argp;
  int res = 0;
  global_State *g = G(L);
  if (g->gcstp & (GCSTPGC | GCSTPCLS))  /* internal stop? */
    return -1;  /* all options are invalid when stopped */
  lua_lock(L);
  va_start(argp, what);
  switch (what) {
    case LUA_GCSTOP: {
      g->gcstp = GCSTPUSR;  /* stopped by the user */
      break;
    }
    case LUA_GCRESTART: {
      luaE_setdebt(g, 0);
      g->gcstp = 0;  /* (other bits must be zero here) */
      break;
    }
    case LUA_GCCOLLECT: {
      luaC_fullgc(L, 0);
      break;
    }
    case LUA_GCCOUNT: {
      /* GC values are expressed in Kbytes: #bytes/2^10 */
      res = cast_int(gettotalbytes(g) >> 10);
      break;
    }
    case LUA_GCCOUNTB: {
      res = cast_int(gettotalbytes(g) & 0x3ff);
      break;
    }
    case LUA_GCSTEP: {
      lu_byte oldstp = g->gcstp;
      l_mem n = cast(l_mem, va_arg(argp, size_t));
      int work = 0;  /* true if GC did some work */
      g->gcstp = 0;  /* allow GC to run (other bits must be zero here) */
      if (n <= 0)
        n = g->GCdebt;  /* force to run one basic step */
      luaE_setdebt(g, g->GCdebt - n);
      luaC_condGC(L, (void)0, work = 1);
      if (work && g->gcstate == GCSpause)  /* end of cycle? */
        res = 1;  /* signal it */
      g->gcstp = oldstp;  /* restore previous state */
      break;
    }
    case LUA_GCISRUNNING: {
      res = gcrunning(g);
      break;
    }
    case LUA_GCGEN: {
      res = (g->gckind == KGC_INC) ? LUA_GCINC : LUA_GCGEN;
      luaC_changemode(L, KGC_GENMINOR);
      break;
    }
    case LUA_GCINC: {
      res = (g->gckind == KGC_INC) ? LUA_GCINC : LUA_GCGEN;
      luaC_changemode(L, KGC_INC);
      break;