[dmd-concurrency] Sending mesages to non-listening threads

[Robert Jacques]

On Wed, 13 Jan 2010 13:49:49 -0500, Andrei Alexandrescu  
<andrei at erdani.com> wrote:
> Robert Jacques wrote:
>> Erlang uses "passers" all the time. The difference is spinning off an  
>> Erlang process is no big deal, so you don't think about it. Spinning  
>> off an OS thread, on the other hand, is a big deal.
>
> Point taken. BTW we should reserve the possibility to implement abstract  
> threads in D as well. I wonder how Erlang achieves its good performance  
> numbers.

A key thing to remember is that Erlang's runtime is actually serial: on  
multi-core machines it simply spawns multiple processes. This is a great  
and efficient paradigm, (It makes the GC thread-local, etc) but it's  
somewhat all or none. There are lot's of issues with mixing fibers and  
threads without operating system support. I know it's broken pre-Vista on  
Windows, because certain OS calls make some poor assumptions, resulting is  
rare hard to track down bugs. I also know this effect third party  
libraries do this too (OpenGL drivers, etc.). I don't know if the *nix  
world has any hidden gotchas like that. I think message passing should  
cleanly support D fibers, and we should encourage their usage: programming  
with threads doesn't scale since inevitably you either have too many or  
not enough.

One way to mitigate this is to have a task library like cilk or Intel's  
Threading Building blocks.