Interesting Thread Gotcha

Diez B. Roggisch deets at nospam.web.de
Wed Jan 16 19:33:09 CET 2008


Dan schrieb:
> On Jan 16, 11:06 am, "Diez B. Roggisch" <de... at nospam.web.de> wrote:
>> Hendrik van Rooyen wrote:
>>> "Dan" <the,,,ail.com> wrote:
>>>>>>> keyboard_thread = thread.start_new_thread(kbd_driver (port_q,kbd_q))
>>>> Needs to be
>>>>>>> keyboard_thread = thread.start_new_thread(kbd_driver, (port_q,kbd_q))
>>>> Commas are important!
>>>> -Dan
>>> Absolutely! - well spotted!
>>> As the first correct respondent, you win the freedom to spend a week in
>>> Naboomspruit at your own expense.
>>> It would have been nice, however, to have gotten something like:
>>> TypeError - This routine needs a tuple.
>>> instead of the silent in line calling of the routine in question,
>>> while failing actually to start a new thread.
>> You can't prevent the silent inline-calling - otherwise, how would you do
>> this:
>>
>> def compute_thread_target():
>>     def target():
>>         pass
>>     return target
>>
>> thread.start_new_thread(compute_thread_target())
>>
>> Of course start_new_thread could throw an error if it got nothing callable
>> as first argument. No idea why it doesn't.
>>
>> Diez
> 
> Of course, in his case, having start_new_thread throw an error
> wouldn't have helped, since he went into an infinite loop while
> evaluating the parameters for start_new_thread.
> 
> Would it be possible to have pychecker (or some such) warn that there
> is an insufficient parameter count to start_new_thread? I guess that
> would require knowing the type of thread. . .

What has this to do with the second argument? It's perfectly legal to 
have a function as thread-target that takes no arguments at all, so 
enforcing a second argument wouldn't be helpful - all it would do is to 
force all developers that don't need an argument tuple to pass the empty 
tuple. So there was no insufficient argument count.

And none of these would solve the underlying problem that in python 
expressions are evaluated eagerly. Changing that would mean that you end 
up with a totally new language.

the only thing that could help to a certain extend would be static 
types. Which we don't want here :)

Diez



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