多线程下的线程执行顺序问题

CODE:

import thread, time

def counter(myId, count):
    for i in range(count):
        mutex.acquire( )
        time.sleep(1)
        print '[%s] => %s' % (myId, i)
        mutex.release( )

mutex = thread.allocate_lock( )
for i in range(10):
    thread.start_new_thread(counter, (i, 3))

time.sleep(60)
print 'Main thread exiting.'

CODE:

[0] => 0
[0] => 1
[0] => 2
[3] => 0
[3] => 1
[3] => 2
[6] => 0
[6] => 1
[6] => 2
[9] => 0
[9] => 1
[9] => 2
[4] => 0
[4] => 1
[4] => 2
[8] => 0
[8] => 1
[8] => 2
[5] => 0
[5] => 1
[5] => 2
[2] => 0
[2] => 1
[2] => 2
[7] => 0
[7] => 1
[7] => 2
[1] => 0
[1] => 1
[1] => 2
Main thread exiting.