rb_thread_sleep   447 include/ruby/intern.h void rb_thread_sleep(int);
rb_thread_sleep  6009 io.c           		rb_thread_sleep(1);
rb_thread_sleep  3232 process.c                  rb_thread_sleep(1);
rb_thread_sleep  3236 process.c                  rb_protect((VALUE (*)())rb_thread_sleep, 1, &state);