jupyter笔记本中进行多处理与线程处理

Question

我尝试在here处测试示例，将其从线程更改为多处理。

在jupyter笔记本中运行此示例（原始示例），将显示一个进度条，该条会在一段时间内填满。

import threading
from IPython.display import display
import ipywidgets as widgets
import time
progress = widgets.FloatProgress(value=0.0, min=0.0, max=1.0)

def work(progress):
    total = 100
    for i in range(total):
        time.sleep(0.2)
        progress.value = float(i+1)/total

thread = threading.Thread(target=work, args=(progress,))
display(progress)
thread.start()

如果我将代码更改为多处理，则会出现进度条，但不会填满：

import multiprocessing as mp
from IPython.display import display
import ipywidgets as widgets
import time
progress = widgets.FloatProgress(value=0.0, min=0.0, max=1.0)

def work(progress):
    total = 100
    for i in range(total):
        time.sleep(0.2)
        progress.value = float(i+1)/total

p = mp.Process(target = work, args=(progress,))
display(progress)
p.start()

如果我通过在worker循环中添加print(i)来修改上述内容，进度条将神奇地开始填充。

import multiprocessing as mp
from IPython.display import display
import ipywidgets as widgets
import time
progress = widgets.FloatProgress(value=0.0, min=0.0, max=1.0)

def work(progress):
    total = 100
    for i in range(total):
        print(i)
        time.sleep(0.2)
        progress.value = float(i+1)/total

p = mp.Process(target = work, args=(progress,))
display(progress)
p.start()

这是一个错误还是有一些我根本不了解的基本信息？

编辑（系统信息）

OS是Ubuntu 18.04

$jupyter --version 
4.4.0

import sys; sys.version 
3.7.0 (default, Oct 15 2018, 10:26:13) \n[GCC 7.3.0]