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digitalmars.D - DIP-74 Reference Cycles

reply "Per =?UTF-8?B?Tm9yZGzDtnci?= <per.nordlow gmail.com> writes:
I just read http://wiki.dlang.org/DIP74

and I'm very excited about it :)

What are the plans on making it handle RC-cycles using weak and 
strong references?

See also:

https://en.wikipedia.org/wiki/Reference_counting#Dealing_with_reference_cycles
Jul 08 2015
parent reply "Martin Nowak" <code dawg.eu> writes:
On Wednesday, 8 July 2015 at 11:39:27 UTC, Per Nordlöw wrote:

 I just read http://wiki.dlang.org/DIP74

 and I'm very excited about it :)

 What are the plans on making it handle RC-cycles using weak and 
 strong references?

 See also:

 https://en.wikipedia.org/wiki/Reference_counting#Dealing_with_reference_cycles


We're currently overhauling smart ptrs, like Unique and 
RefCounted.
Among others we'll add class support, rendering most of DIP74 
superfluous.
Jul 08 2015
parent reply =?UTF-8?B?Ik5vcmRsw7Z3Ig==?= <per.nordlow gmail.com> writes:
On Wednesday, 8 July 2015 at 21:55:49 UTC, Martin Nowak wrote:

 We're currently overhauling smart ptrs, like Unique and 
 RefCounted.
 Among others we'll add class support, rendering most of DIP74 
 superfluous.


But not everything in DIP74 can be implemented as library 
extension right?
Jul 09 2015
parent reply "deadalnix" <deadalnix gmail.com> writes:
On Thursday, 9 July 2015 at 08:31:39 UTC, Nordlöw wrote:

 On Wednesday, 8 July 2015 at 21:55:49 UTC, Martin Nowak wrote:

 We're currently overhauling smart ptrs, like Unique and 
 RefCounted.
 Among others we'll add class support, rendering most of DIP74 
 superfluous.


 But not everything in DIP74 can be implemented as library 
 extension right?


The escape analysis needs to be in the compiler. Proposed DIPs do 
a poor job at it as they require a bag of tricks instead of a 
principled approach IMO.

The part where refcount is done can be done via library (and 
should IMO).
Jul 09 2015
next sibling parent reply "Brad Anderson" <eco gnuk.net> writes:
On Thursday, 9 July 2015 at 08:58:22 UTC, deadalnix wrote:

 The part where refcount is done can be done via library (and 
 should IMO).


I think the nice thing about the compiler aware approach is that 
the compiler could forgo incs/decs when it knows the reference 
doesn't escape. I'm not sure how much this would actually aid 
performance in practice though.
Jul 09 2015
parent "deadalnix" <deadalnix gmail.com> writes:
On Thursday, 9 July 2015 at 16:49:53 UTC, Brad Anderson wrote:

 On Thursday, 9 July 2015 at 08:58:22 UTC, deadalnix wrote:

 The part where refcount is done can be done via library (and 
 should IMO).


 I think the nice thing about the compiler aware approach is 
 that the compiler could forgo incs/decs when it knows the 
 reference doesn't escape. I'm not sure how much this would 
 actually aid performance in practice though.


There are one case where it is actually useful: when refcounting 
shared object.

For thread local object, the compiler already have the 
increment/decrement pair and can optimize accordingly. It can't 
when the refcount is shared (it always is in many languages like 
C++ or ObjC) because another thread could have done arbitrary 
thing to the refcount in the meantime. In that case it is useful, 
but generally, refcounting shared object have loosy perfs because 
of contention on the cache line containing the refcount.

The other case where refcounting is bad is when it interract with 
exceptions. In which case, the language improvement we are 
talking about here do not help much, and this is why exception 
are not recoverable in ObjC and absent in swift. A option to make 
them fast again would be to not decrement the refcount on 
unwinding, and leak, delegating the cleanup to the GC.
Jul 09 2015
prev sibling parent "Martin Nowak" <code dawg.eu> writes:
On Thursday, 9 July 2015 at 08:58:22 UTC, deadalnix wrote:

 The escape analysis needs to be in the compiler. Proposed DIPs 
 do a poor job at it as they require a bag of tricks instead of 
 a principled approach IMO.

 The part where refcount is done can be done via library (and 
 should IMO).


Right, there are a number of proposals to make a library 
implementation powerful enough.
http://wiki.dlang.org/DIP69#Scope_Function_Returns
http://wiki.dlang.org/DIP77
Jul 10 2015