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

[Ron Adam]

On 08/20/2015 11:45 AM, Sven R. Kunze wrote:
> 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.

When a bytecode to load an object is executed such as LOAD_FAST, it gets 
it's reference to the object from the function's list of names in it's 
code object.

 >>> def foo(x):
...     y = 2
...     return x + y
...
 >>> from dis import dis
 >>> dis(foo)
   2           0 LOAD_CONST               1 (2)
               3 STORE_FAST               1 (y)

   3           6 LOAD_FAST                0 (x)
               9 LOAD_FAST                1 (y)
              12 BINARY_ADD
              13 RETURN_VALUE

 >>> dir(foo.__code__)
['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', 
'__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', 
'__init__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', 
'__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', 
'__subclasshook__', 'co_argcount', 'co_cellvars', 'co_code', 
'co_consts', 'co_filename', 'co_firstlineno', 'co_flags', 'co_freevars', 
'co_kwonlyargcount', 'co_lnotab', 'co_name', 'co_names', 'co_nlocals', 
'co_stacksize', 'co_varnames']

 >>> foo.__code__.co_varnames
('x', 'y')

LOAD_FAST 0,  reads __code__.co_varnames[0]
LOAD_FAST 1,  reads __code__.co_varnames[1]

Adding a co_mutables name list to the __code__ attribute, along with new 
bytecodes to access them, it would create a way to keep private local 
names without changing how the other bytecodes work.

LOAD_MUTABLE 0,  would get the first reference in __code__.co_mutables.


Look for co_name, and co_freevars here to see how they relate to other 
byte codes.

https://docs.python.org/3.5/library/dis.html#python-bytecode-instructions


Hope that helps.

Cheers,
    Ron










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