From: Robert Klemme <bob.news@...>
Date: 2004-02-09T19:04:59+09:00
Subject: Re: Multi-threading lesson wanted


"Charles Comstock" <cc1@cec.wustl.edu> schrieb im Newsbeitrag
news:c07jo8$l5f$1@newsreader.wustl.edu...
> Robert Klemme wrote:
>
> > "Tim Bates" <tim@bates.id.au> schrieb im Newsbeitrag
> > news:4025CA70.9090202@bates.id.au...
> > <snip>
> >
> >>Below is the code I have written. The idea is that other application
> >>code calls SAMS::Database.get_handle{ |handle| handle.execute... } and
> >>this module takes care of the rest. Also, the application's shutdown
> >>code will call SAMS::Database.destroy to cleanly disconnect all the
> >
> > handles.
> >
> > You definitely need some kind of synchronization mechanism that makes
> > accesses to the shared connection pool thread safe.  In your case a
> > ConditionVariable will help you with the max connection logic.
> >
> > See section "Logging from multiple threads" for example usage of a
> > ConditionVariable at
> > http://www.rubygarden.org/ruby?MultiThreading
> >
> > I'd implement a Semaphore using a ConditionVariable and a Mutex; that
way
> > you can initialize the semaphore with the max connection value and
count
> > the semaphore down when you take a connection from the pool and
increment
> > it when you put it back.  If the semaphore is zero, the next thread
trying
> > to decrease the semaphore is put to sleep and will wake up when
another
> > thread increments the semaphore.
> >
> > You can as well use the semaphore implementation in the RAA:
> > http://raa.ruby-lang.org/list.rhtml?name=semaphore
> >
> > <snip>
> >
> > As an additional note: I would not use module methods for the pool
> > handling.  Instead I'd instantiate an instance of the pool.  This is
IMHO
> > better since the pool is not necessarily a singleton: Just think of an
> > application that needs to access more than one database and hence use
more
> > than one connection configuration.
> >
> > Kind regards
> >
> >     robert
> >
> Why doesn't the counting semaphore library come standard with Ruby?

Dunno.

>  I
> haven't done anything multithreaded in a little while, but I remember
> being annoyed I didn't have a counting semaphore.  Is there a particular
> reason it's not part of the standard library?  Obviously not everything
> should come standard but this seems to be the sort of thing that should.

Yeah, that's true.  +1 for including Semaphore in "Thread".  Matz?

Regards

    robert