Remember that Go vs D MQTT thing and how we wondered about dmd vs gdc?

[Shammah Chancellor]

On 2014-03-07 21:11:12 +0000, Bienlein said:

> What they are saying on their web site is that they are using fibers 
> and at the same time they say they are using libevent. That is 
> confusing for me. On http://vibed.org/features they write: "Instead of 
> using classic blocking I/O together with multi-threading for doing 
> parallel network and file operations, all operations are using 
> asynchronous operating system APIs. By default, >>libevent<< is used to 
> access these APIs operating system independently."
> 
> Further up on the same page they write: "The approach of vibe.d is to 
> use asynchronous I/O under the hood, but at the same time make it seem 
> as if all operations were synchronous and blocking, just like ordinary 
> I/O. What makes this possible is D's support for so called >>fibers<<".

That is all correct.  Libevent supplies the polling an async io.   D 
provides the ability to do fibers.   Mixed together you get a very 
probust, easy to program, scalable, web platform.   See below.

> 
>> It does. Bienlein has a very vague knowledge of topics he
>> comments about.
> 
> I thought the vibe.d guys would shed some light at this at the 
> occasion, but no luck. What I don't understand is how fibers can listen 
> to input that comes in through connections they hold on to. AFAIKS, a 
> fiber only becomes active when it's call method is called. So who calls 
> the call method in case a connection becomes active? That is then again 
> a kernel thread? How does the kernel thread know something arrived 
> through a connection? It can't do a blocking wait as the system would 
> run out of kernel threads very quickly.

Fibers are cooperatively multitasked routines.  Whenever vibe-d uses a 
libevent IO function, it yields it's current operation back to the 
event loop.  When a libevent poll indicates there is data waiting, it 
resumes that fiber where it was left off.   The vibe-d event loop is 
essentially the scheduler for the fibers.