RE: [ECOS] POSIX Queue Suspension

[Gary Thomas <gary@chez-thomas.org>]

On Mon, 2005-06-20 at 16:58 -0500, Ali, Khurram wrote:
> FYI
> 
> I got the latest source using anonymous cvs. Used the default
> configuration with POSIX support. I see the behavior which I was
> expecting.
> 
> I now have another question: How do I add support for printf? Which
> library is this part of? I am using an x86 PC as my target.
> 

What kind of support do you think you need?  If you have the POSIX
environment running, you've everything already.

Perhaps you're asking about [interrupt driven] serial drivers?

> Thank you,
> Khurram
> 
> -----Original Message-----
> From: ecos-discuss-owner@ecos.sourceware.org
> [mailto:ecos-discuss-owner@ecos.sourceware.org] On Behalf Of Ali,
> Khurram
> Sent: Monday, June 20, 2005 1:49 PM
> To: Andrew Lunn
> Cc: eCos Discussion
> Subject: RE: [ECOS] POSIX Queue Suspension
> 
> > If more than one thread is waiting to receive a message when a message
> > arrives at an empty queue and the Priority Scheduling option is
> supported, 
> > then the thread of highest priority that has been waiting the longest 
> > shall be selected to receive the message.
> 
> Thread L is the highest priority thread that has been waiting the
> longest. Shouldn't it be resumed first?
> 
> Agreed that other threads also have the same priority, but since there
> is an additional restriction of "waiting the longest" I would assume
> that we can have two or more threads at the same priority?
> 
> Am I missing something?
> 
> Khurram
> 
> -----Original Message-----
> From: Andrew Lunn [mailto:andrew@lunn.ch] 
> Sent: Monday, June 20, 2005 12:22 PM
> To: Ali, Khurram
> Cc: eCos Discussion
> Subject: Re: [ECOS] POSIX Queue Suspension
> 
> On Mon, Jun 20, 2005 at 10:54:00AM -0500, Ali, Khurram wrote:
> > Hello,
> > 
> > I have two POSIX threads that are waiting to receive on a POSIX queue.
> > Thread L suspends on the queue first. Thread K then suspends on the
> > queue. However, when Thread J sends an element to the queue. Thread K
> is
> > resumed first. 
> > 
> > All threads have the same priority. All queue accesses are also made
> > with the same priority. Shouldn't Thread L be resumed first. 
> > 
> > What could I be doing wrong?
> 
> You don't seem to of read the POSIX standard. 
> 
> http://www.opengroup.org/onlinepubs/009695399/functions/mq_receive.html
> 
> If the specified message queue is empty and O_NONBLOCK is not set in
> the message queue description associated with mqdes, mq_receive()
> shall block until a message is enqueued on the message queue or until
> mq_receive() is interrupted by a signal. If more than one thread is
> waiting to receive a message when a message arrives at an empty queue
> and the Priority Scheduling option is supported, then the thread of
> highest priority that has been waiting the longest shall be selected
> to receive the message. Otherwise, it is unspecified which waiting
> thread receives the message. If the specified message queue is empty
> and O_NONBLOCK is set in the message queue description associated with
> mqdes, no message shall be removed from the queue, and mq_receive()
> shall return an error.
> 
> So eCos behavious seems correct to me.
> 
>         Andrew
> 
> -- 
> Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
> and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss
> 
> 
-- 
Gary Thomas <gary@chez-thomas.org>


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