What causes a call to queue.join () in the main thread for non-main threads?

Question

My code is as follows:

import time, queue, threading

def washer(dishes, dish_queue): 
    for dish in dishes: 
        print ("Washing", dish) 
        time.sleep(1) 
        dish_queue.put(dish)

def dryer(dish_queue): 
    while True: 
        dish = dish_queue.get() 
        print("Drying", dish) 
        time.sleep(2) 
        dish_queue.task_done()
        print('dryer')

dish_queue = queue.Queue()
for n in range(2): 
    dryer_thread = threading.Thread(target=dryer, args=(dish_queue,))
    dryer_thread.start()

dishes = ['salad', 'bread', 'entree', 'desert'] 
washer(dishes, dish_queue) 
dish_queue.join()

From my understanding of the documentation documentation in turn, dish_queue.join () will block the main thread until the number of unfinished tasks (unreadable dishes here) returns to 0. But I wonder what happened with 2 dry_thread.

I found that if I run the function dryeron an empty one dish_queuein the main program, the program gets stuck (BTW, is this the so-called block from dish_queue.get ()?). So if dish_queue.join()unlocks the main thread, make 2 dry_thread also unlocked and free up memory? What does a block in a queue in a doc mean ?

Answer 1

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