[Lcd4linux-devel] Threads

[Michael R. <re...@eu...>]

Hi Xavier, Hi List,

> Okay, I was misinformed about fork. Let's continue this way.
I already started with a "simple threading" framework (nothing in CVS by 
now)

> But another question : for example eval needs the mail('unread') value,
> so calls a (hypothetical) mail() function in plugin_mail, which forks to
> retreive POP summary, and it takes, for example, 5 seconds, what does
> the eval do within this time ? I don't know what Michael wants on this
> issue.

It's simple: The first call to mail::unread() triggers the fork, and 
returns nothing (this is a drawback: oin the first call you'll never get 
a senseful result). From now on, the 2nd thread regularly polls the 
mailbox (at a configurable interval from the config file), ans stores 
the result in a special shared memory area. The main thread from 
mail::unread() does nothing but reading this shared memory area and 
returns the corresponding results. So the main thread is very fast and 
does never block.

The shared memory area itself will be protected by a mutex, to ensure 
that it's not written to by the poll thread while being read from the 
mail thread.

The best place for such a "shared memory parameter passing structure" 
would be our well-loved hash. But I'm not shure if this is possible...

I am starting this async stuff with the exec() plugin, because its 
simpler than POP polling, so I can focus on the threading framework. 
Exec's really need an async model, too, because you never can tell how 
long the exec'ed prcess will take today.


bye, Michael

-- 
Michael Reinelt                                   Tel: +43 676 3079941
Geisslergasse 4                                   Fax: +43 316  692343
A-8045 Graz, Austria                          e-mail: re...@eu...