Python 线程 - 在 join() 时做一些事情

Question

Python 2.6.6

我有一个要执行的线程列表，主代码将等待 (Threading.join()) 直到它们全部完成。

>>> for thread in threadList:
...     thread.start()
>>> for t in threadList:
...     t.join()

有没有办法在主代码等待线程结束时打印诸如“正在运行...”之类的消息？

我想一秒又一秒地打印相同的东西（“正在运行...”），直到线程全部完成。

谢谢。

---

已解决

实施的解决方案：

>>> for thread in threadList:
...     thread.start()
>>> string = "running"
>>> while any(t.is_alive() for t in threadList):
...    sys.stdout.write("\r%s" % string)
...    sys.stdout.flush()
...    string = string + "."                     #this may not be the best way
...    time.sleep(0.5)

在我的情况下，“time.sleep(0.5)”的额外时间不是问题，尽管它不是最推荐的。

这会生成输出：

running........

“running”之后的点将一个接一个地打印在同一行，同时还有任何线程处于活动状态。果然如我所料！

基于@Manuel Jacob 和@Alex Hall 的回答。

Answer 1

Thread.join() 被设计为阻塞。您可以定期调用 Thread.is_alive()，而不是使用 Thread.join()。

您的示例已改编：

for thread in threadList:
    thread.start()
while any(thread.is_alive() for thread in threadList):
    print('running...')
    time.sleep(1)

正如 cmets 中所指出的，当最后一个线程在睡眠期间完成时，这可能会导致最多一秒的额外延迟。

Answer 2

from time import sleep
from threading import Thread

threadList = [Thread(target=lambda: sleep(3)), Thread(target=lambda: sleep(5))]

for thread in threadList:
    thread.start()

def check_running():
    while True:
        alive = sum(thread.is_alive() for thread in threadList)
        if not alive:
            break
        print '%s threads still running...' % alive
        sleep(1)

Thread(target=check_running).start()

for t in threadList:
    t.join()

输出：

2 threads still running...
2 threads still running...
2 threads still running...
1 threads still running...
1 threads still running...

---

或者：

from time import sleep
from threading import Thread

threadList = [Thread(target=lambda: sleep(3), name='Alice'), Thread(target=lambda: sleep(5), name='Bob')]

for thread in threadList:
    thread.start()

for t in threadList:
    while True:
        t.join(timeout=1)
        if not t.is_alive():
            break
        print('%s is still running...' % t.name)

输出：

Alice is still running...
Alice is still running...
Bob is still running...