Re: Help writing first daemon

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Tue, 11 Sep 2012 13:50:27 -0700 (PDT), Maciej Sobczak wrote:

> W dniu wtorek, 11 wrze�nia 2012 17:13:06 UTC+2 u�ytkownik Dmitry A. Kazakov napisa�:
> 
>>>> But, if you consider running the middleware as a system service (daemon),
>>>> the main reason for that would be the architecture of shared memory.
>>> 
>>> No, there is no connection between these two concepts.
>> 
>> The concepts are single vs. multiple instances middleware.
> 
> No. System services and shared memory are low-level building blocks that
> can be used to construct software that actually does something useful.
> Whether that software exists in a single vs. multiple instances is a
> matter of terminology that is defined on a much higher level and has
> nothing to do with how many processes there are or how they communicate.

Not the software, but states (and thus data). In a single instance
middleware objects maintained by it are physically shared by all
applications. That precludes I/O, like pipes. In a multiple instances
middleware objects are replicated and some I/O is necessary to maintain
consistency of a logical object, physically distributed across
applications.

> For example, a well known database server is said to exist in a single
> instance, while being physically composed of many processes (presumably
> system services) communicating with each other. These concepts exist on
> different levels.

E.g. DB vs. DB replica.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de