pthread_create doesn't run

```
void *thr_fn(void *arg)
{
printf("this is a new thread\n");
int i;
while(1)
{
printf("%d\n", i);
emscripten_thread_sleep(200);
i++;
}
}

int EMSCRIPTEN_KEEPALIVE create_thread()
{
printf("this is create\n");
pthread_t ntid;
pthread_create(&ntid, NULL, thr_fn, NULL);
while(1)
{
emscripten_thread_sleep(200);
}
}
```
When I use the "create_thread" in a Web Worker, it seems to not run an not printf any number.