[Twisted-Python] deferToThread question

[Michele Petrazzo]

I want to call a block function. I use deferToThread to call it, so 
something like this:

def block_func():
  os.popen3(my_soft) #my_soft is a blocking software
  print 1/0 # Simulate an error

If I use normal (not defer) call, so: block_func(), the exception is 
raised after my_soft is closed.

I i call block_func with defer, so:

def block_func_err(err):
  print err

t = threads.deferToThread(block_func)
t.addErrback(block_func_err)

the error is raised before my_soft is closed.

Why? Is it right?

S.O. win2k and mdk10, both with py 2.3.4, twisted 1.3.0, wxpy 2.4.2 and 
user of wxsupport, not wxreactor.

Thanks,
Michele Petrazzo