Python IDLE与多线程兼容？

Question

It seems that IDLE (part of the standard Python Windows install) will not execute multithreaded programs correctly without nasty hangs or bugout crashes. Does anyone know of a way to fix this?

The following program will always hang in IDLE but complete normally when executed with the Python interpreter directly:

import threading, time

printLock = threading.Lock()

def pl(s):
  printLock.acquire()
  print s
  printLock.release()

class myThread( threading.Thread ):
  def run(self):
    i = 0
    for i in range(0,30):
      pl(i)
      time.sleep(0.1)

t = myThread()
t.start()

while threading.activeCount() > 1:
  time.sleep(1)
  pl( time.time() )

print "all done!"

sample output:

U:\dev\py\multithreadtest>python mt.py
0
1
2
3
4
5
6
7
8
9
1277935368.84
10
11
12
13
14
15
16
17
18
19
1277935369.84
20
21
22
23
24
25
26
27
28
29
1277935370.84
1277935371.84
all done!

output when using IDLE "Run Module" function always hangs indefinitely at around the time the line reading 23 or 24 shows up on my machine.

Answer 1

import threading
print(threading.activeCount())

prints 1 when run at the command line, 2 when run from Idle. So your loop

while threading.activeCount() > 1:
  time.sleep(1)
  pl( time.time() )

will terminate in the console but continue forever in Idle.

To fix the problem in the posted code, add something like

initial_threads = threading.activeCount()

after the import and change the loop header to

while threading.activeCount() > initial_threads:

With this change, the code runs through 30 cycles and stops with 'all done!'. I have added this to my list of console Python versus Idle differences that need to be documented.

Answer 2

IDLE has some known issues when it comes to threading. I don't know an overwhelming amount about the particulars of why it's an issue, because I try my very hardest to stay away from IDLE, but I know that it is. I would strongly suggest you just go get IronPython and Python Tools for Visual Studio. VS's debugging tools are absolutely unmatched, especially given the huge library of add-ons.

Answer 3

AFAIK it's a crapshoot when running threaded code in IDLE. IDLE uses the GIL liberally so race conditions and deadlocks are common. Unfortunately, I am not well versed enough in threading to offer insight on making this thread-safe, beyond the obvious.