[dmd-concurrency] catching up

[Andrei Alexandrescu]

The most significant bits are:

* D's concurrency approach flagship is a message passing architecture 
similar to Erlang's. The message passing design must work across (a) 
threads within the same address space; (b) processes within the same 
machine; (c) machines within the same subnet; (d) arbitrary remote 
machines. Depending on cases (a)-(d) there are different strategies of 
passing data around, e.g. within the same address space immutable data 
may be shared and shared objects may be aliased. To some extent, 
however, user code should be able to send a message to a concurrent 
entity without knowing or caring where the entity is, and what transport 
method is used. We don't yet have a detailed design for this.

* By default there is no data sharing across threads.

* The shared qualifier allows explicit sharing. The compiler guarantees 
statically that all mutable shared data is actually marked as shared. 
__gshared will remain a low-level mechanism to cheat on that guarantee, 
and we hope to be able to remove that in the future.

* One issue is how shared interacts with synchronized. I'll email about 
this in a different message.

* One issue is initializing shared and non-shared (TLS) globals. We will 
have "static this()" be invoked for every thread and define the new 
module constructor "static shared this()" that is only invoked upon the 
start of the process.


Andrei

Graham St Jack wrote:
> I'm also in need of a catch-up briefing.
> 
> Thanks,
> Graham
> 
> Kevin Bealer wrote:
>> Beginner stuff...
>>
>> Andrei mentioned that there have been many months of mulling over 
>> models and
>> options.  Is there a description of what has been figured out so far 
>> and what's left
>> to do?  Is there a place where I can get caught up on the vision so far?
>>
>> Topics I know about so far:
>> - Sean Kelley is working on a message passing system
>> - Immutable / pure logic should make concurrent code faster, safer, better
>> - Globals default to TLS unless shared is used.
>>
>> For people joining this group it would be good to have a sort of 
>> bullet point list of
>> what questions have been answered and what still has to be worked out.
>>
>> What are the big unanswered questions?
>>
>> Thanks,
>> Kevin
>>
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