[Python-Dev] Re: [Stackless] comments on PEP 219
jeremy at alum.mit.edu
Wed Mar 14 02:17:39 CET 2001
>>>>> "GMcM" == Gordon McMillan <gmcm at hypernet.com> writes:
>> Is this the semantic difference between Stackless and CPython
>> that people are getting all in a lather about?
GMcM> What semantic difference? You can't transfer control to a
GMcM> coroutine / urthread in a magic method in CPython, either
If I have a library or class that uses threads under the covers, I can
create the threads in whatever code block I want, regardless of what
is on the call stack above the block. The reason that coroutines /
uthreads are different is that the semantics of control transfers are
tied to what the call stack looks like a) when the thread is created
and b) when a control transfer is attempted.
This restriction seems quite at odds with modularity. (Could I import
a module that creates a thread within an __init__ method?) The
correctness of a library or class depends on the entire call chain
involved in its use.
It's not at all modular, because a programmer could make a local
decision about organizing a particular module and cause errors in a
module that don't even use directly. This would occur if module A
uses uthreads, module B is a client of module A, and the user writes a
program that uses module B. He unsuspectingly adds a call to module A
in an __init__ method and *boom*.
"Python is a language in which the use of uthreads in a module you
didn't know existed can render your own program unusable." <wink>
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