emb_free_embedded_thd is not thread safe

static void emb_free_embedded_thd(MYSQL *mysql)
{
THD thd= (THD)mysql->thd;
thd->clear_data_list();
thread_count--;
thd->store_globals();
thd->unlink();
delete thd;
my_pthread_setspecific_ptr(THR_THD, 0);
mysql->thd=0;
}

thread_count is global but it is modified without protection. In a multi-core env this will lead to lost updates or at least, race conditions.