at-exit-thread

[Gabriel Genellina]

En Fri, 29 Feb 2008 18:12:13 -0200, <castironpi at gmail.com> escribió:

> On Feb 29, 1:55 pm, "Diez B. Roggisch" <de... at nospam.web.de> wrote:
>> castiro... at gmail.com schrieb:
>>
>> > The Python main interpreter has an at-exit list of callables, which
>> > are called when the interpreter exits.  Can threads have one?  What's
>> > involved, or is the best way merely to subclass Thread?
>>
>> Is that some sort of trick-question?
>>
>> class MyThread(Thread):
>>
>>     def run(self):
>>         while some_condition:
>>              do_something()
>>         do_something_after_the_thread_ends()
>>
>> The atexit stuff is for process-termination which is/may be induced by
>> external signals - which is the reason why these callbacks extist.
>> Threads don't have that, thus no need.
>
> That depends.  If a thread adds an object it creates to a nonlocal
> collection, such as a class-static set, does it have to maintain a
> list of all such objects, just to get the right ones destroyed on
> completion?

Yes, like any other objects. All threads in a process share the same  
memory space; any thread can "see" any other created object, and the  
general rules on reference counting apply: an object is destroyed when it  
is no more referenced.
There are threading.local objects, which are specially designed to provide  
per-thread storage; they are not shared among threads. (BTW, you should  
use a threading.local instance instead of indexing by get_ident())

> Processes destroy their garbage hassle-free; how can
> threads?  And don't forget Thread.run( self ) in the example, if
> anyone ever wants to make use of the 'target' keyword.

Any object created inside a thread will be destroyed when the last  
reference to it is removed, as any other object. Threads are not special  
in this regard.

-- 
Gabriel Genellina