[Python-ideas] easy thread-safety [was: fork]

[Sven R. Kunze]

On 20.08.2015 04:20, Ron Adam wrote:
> In this case 'i' is immutable as it's not marked as 'mutable'.  That 
> determines what byte code is used, (or how the byte code that is used 
> acts).
>
> >>> dis(spam)
>   2           0 SETUP_LOOP              24 (to 27)
>               3 LOAD_FAST                0 (a)
>               6 GET_ITER
>         >>    7 FOR_ITER                16 (to 26)
>              10 STORE_FAST               1 (i)
>
>   3          13 LOAD_GLOBAL              0 (eggs)
>              16 LOAD_FAST                1 (i)
>              19 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
>              22 POP_TOP
>              23 JUMP_ABSOLUTE            7
>         >>   26 POP_BLOCK
>         >>   27 LOAD_CONST               0 (None)
>              30 RETURN_VALUE
>
> If a compiler directive/flag for threading was set, then the 
> interpreter/compiler may use different LOAD_FAST and GET_ITER routines 
> that will raise an exception if "i" or "a" is mutable. (by checking a 
> flag on the object, or other means.)
>
> If however...
>
>     def eggs(i):
>         mutable i       # mutable objects clearly marked.
>         i.scramble()
>
>     def spam(a):
>         mutable a, i
>         for i in a:
>             eggs(i)    # eggs can't access 'a' or 'i' in it's scope.
>                        # so i needs to be passed.

I had absolutely not idea what you mean when saying: "co_mutables". 
Reading the byte code and the examples above though, I just can agree. 
Thanks a lot for this.

Yesterday, I used "shared" in my posts to illustrate that. "mutable" is 
another word for it.

Best,
Sven