TLBB: The Last Big Breakage

[Dicebot]

On Sunday, 16 March 2014 at 04:08:15 UTC, Andrei Alexandrescu 
wrote:
> D1's approach to multithreading was wanting. D2 executed a big 
> departure from that with the shared qualifier and the 
> default-thread-local approach to data.
>
> We think this is a win, but D2 inherited a lot of D1's 
> thread-related behavior by default, and some of the rules 
> introduced by TDPL (http://goo.gl/9gtH0g) remained in the "I 
> have a dream" stage.
>
> Fixing that has not gained focus until recently, when e.g. 
> https://github.com/D-Programming-Language/dmd/pull/3067 has 
> come about. There is other more stringent control of shared 
> members, e.g. "synchronized" is all or none, "synchronized" 
> only makes direct member variables unshared, and more.
>
> This will statically break code. It will refuse to compile code 
> that is incorrect, but also plenty of code that is correct; the 
> compiler will demand extra guarantees from user code, be they 
> in the form of casts and stated assumptions.
>
> I believe this is a bridge we do need to cross. One question is 
> how we go about it: all at once, or gradually?
>
>
> Andrei

I still have zero understanding of what "synchronized" is 
supposed to mean an only vague guesses about "shared". Probably 
have never used either of those apart of "shared static this()" 
module constructors. Having some examples of how code is supposed 
to behave and what will break can help reason about it.