Threadpools, difference between DMD and LDC

[Dicebot via Digitalmars-d-learn]

On Monday, 4 August 2014 at 16:38:24 UTC, Russel Winder via 
Digitalmars-d-learn wrote:
>> Modern default approach is to have amount of "worker" threads 
>> identical or close to amount of CPU cores and handle internal 
>> scheduling manually via fibers or some similar solution.
>
> I have no current data, but it used to be that for a single 
> system it
> was best to have one or two more threads than the number of 
> cores.
> Processor architectures and caching changes so new data is 
> required. I
> am sure someone somewhere has it though.

This is why I had "or close" remark :) Exact number almost always 
depends on exact deployment layout - i.e. what other processes 
are running in the system, how hardware interrupts are handled 
and so on. It is something to decide for each specific 
application. Sometimes it is even best to have amount of worker 
threads _less_ than amount of CPU cores if affinity is to be used 
for some other background service for example.

>> If you are totally new to the topic of concurrent services, 
>> getting familiar with 
>> http://en.wikipedia.org/wiki/C10k_problem may be useful :)
>
> I thought they'd moved on the the 100k problem.

True, C10K is a solved problem but it is best thing to start with 
to understand why people even bother with all the concurrency 
complexity - all details can be a bit overwhelming if one starts 
completely from scratch.

> There is an issue here that I/O bound concurrency and CPU bound
> concurrency/parallelism are very different beasties. Clearly 
> tools and
> techniques can apply to either or both.

Actually with CSP / actor model one can simply consider 
long-running CPU computation as form of I/O an apply same 
asynchronous design techniques. For example, have separate 
dedicated thread running the computation and send input there via 
message passing - respond message will act similar to I/O 
notification from the OS.

Choosing optimal concurrency architecture for application is 
probably even harder problem than naming identifiers.