Function lua_gc

3rd/lua-5.4.3/src/lapi.c:1126–1221

** 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;
  lua_lock(L);
  g = G(L);
  va_start(argp, what);
  switch (what) {
    case LUA_GCSTOP: {
      g->gcrunning = 0;
      break;
    }
    case LUA_GCRESTART: {
      luaE_setdebt(g, 0);
      g->gcrunning = 1;
      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: {
      int data = va_arg(argp, int);
      l_mem debt = 1;  /* =1 to signal that it did an actual step */
      lu_byte oldrunning = g->gcrunning;
      g->gcrunning = 1;  /* allow GC to run */
      if (data == 0) {
        luaE_setdebt(g, 0);  /* do a basic step */
        luaC_step(L);
      }
      else {  /* add 'data' to total debt */
        debt = cast(l_mem, data) * 1024 + g->GCdebt;
        luaE_setdebt(g, debt);
        luaC_checkGC(L);
      }
      g->gcrunning = oldrunning;  /* restore previous state */
      if (debt > 0 && g->gcstate == GCSpause)  /* end of cycle? */
        res = 1;  /* signal it */
      break;
    }
    case LUA_GCSETPAUSE: {
      int data = va_arg(argp, int);
      res = getgcparam(g->gcpause);
      setgcparam(g->gcpause, data);
      break;
    }
    case LUA_GCSETSTEPMUL: {
      int data = va_arg(argp, int);
      res = getgcparam(g->gcstepmul);