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digitalmars.D - inout(shared) as a thing?

reply Nicholas Wilson <iamthewilsonator hotmail.com> writes:
I was reading 
https://github.com/rikkimax/stdc-signatures/blob/master/stdc
graphic/image.d#L54 as part of
https://github.com/rikkimax/DIPs/blob/master/DIPs/DIP1xxx-RC.md and it struck
me that the duplication of `IFoo` and `ISharedFoo` might be made redundant
`with inout(shared)` as `inout` (->`inout(const)`? so that one can write
`inout(shared,const)`. obviously no need to deprecate plain inout) is to
mutable/const/immutable.

I think this would work for "declarations" like 
interfaces/signatures/contraints, I'm not so sure about 
implementations as the acquisition of ownership needs to occur to 
take place in order to avoid data races.

Maybe inout(shared=(T t){...}) where (T t){...} is a lamda (or 
some other builtin) that ensures that t (or this) is owned by by 
the executing thread. could also have inout(shared=synchronized), 
inout(shared=synchronized(a)) where a is a variable in scope 
(e.g. parameter, member,...), inout(shared=atomic) or some 
wrapper that atomically loads t or this. Just throwing out ideas.

I don't think this would work on the return value of functions.

Thoughts? Worthy of a DIP?

Nic
Feb 07
parent Steven Schveighoffer <schveiguy yahoo.com> writes:
On 2/7/18 5:19 AM, Nicholas Wilson wrote:
 I was reading 
 https://github.com/rikkimax/stdc-signatures/blob/master/stdc
graphic/image.d#L54 
 as part of 
 https://github.com/rikkimax/DIPs/blob/master/DIPs/DIP1xxx-RC.md and it 
 struck me that the duplication of `IFoo` and `ISharedFoo` might be made 
 redundant `with inout(shared)` as `inout` (->`inout(const)`? so that one 
 can write `inout(shared,const)`. obviously no need to deprecate plain 
 inout) is to mutable/const/immutable.
 
 I think this would work for "declarations" like 
 interfaces/signatures/contraints, I'm not so sure about implementations 
 as the acquisition of ownership needs to occur to take place in order to 
 avoid data races.
 
 Maybe inout(shared=(T t){...}) where (T t){...} is a lamda (or some 
 other builtin) that ensures that t (or this) is owned by by the 
 executing thread. could also have inout(shared=synchronized), 
 inout(shared=synchronized(a)) where a is a variable in scope (e.g. 
 parameter, member,...), inout(shared=atomic) or some wrapper that 
 atomically loads t or this. Just throwing out ideas.
 
 I don't think this would work on the return value of functions.
 
 Thoughts? Worthy of a DIP?
I'm thinking it doesn't work. Not because it wouldn't be sound from the standpoint of the type system, but because there is no "possibly shared" type constructor similar to const. If you are inside an inout(shared) function, how do you properly deal with the data? At the moment it's custom based on what your overall structure looks like. Sure, there are atomics for small shared data types, and at that level, you could conservatively just atomically load and store data. But what about shared aggregates? Those require locking at the right places, and there is no compiler-defined way to do it -- you have to write it yourself. There's just no way to do a "maybe shared" implementation for it. -Steve
Feb 07