Re: [Jack-Devel] ringbuffer problems

On April 28, 2011 02:03:07 am Arnold Krille wrote:
> Hi,
>
> On Thursday 28 April 2011 07:28:27 Timothy Godfrey wrote:
>  - Multiple readers in several threads reading from the same ringbuffer.
>
> > Would
> > constitute a violation of the rule, 'Their identities cannot be
> > interchanged'?
>
> This rule is there because when one thread is the reader and then another
> thread starts reading, there is a chance that for a short time both threads
> read. And that is not safe 
Not even reading by two threads is safe? Why is that?
Do you mean 'getting' (removal) from the buffer? That makes sense.
What about simple 'peek' operations (without removal), is that OK? 

> without locks on the ringbuffer or somewhere
> else. (Same for writers.)

MusE is using custom ring buffers. 
(Admittedly I think we're breaking some of those rules in a few places.)
They have some code for atomization with locks, but it seems unused ATM.
I can turn it on, but I wonder if I should.

The ring buffers have a volatile size member.
What effect does the volatile keyword have, in general? 
From the "Introduction to the Volatile Keyword" at Embedded dot com:
"A variable should be declared volatile whenever its value could change 
 unexpectedly.  ...<such as> global variables within a multi-threaded 
 application ...So all shared global variables should be declared volatile."

I try to follow that rule, but I gather use of volatile may not be enough,
 that locks may be required in some cases? 

Thanks. Tim E.

1303975152.32455_0.ltw:2,a <201104280300.21223.termtech at rogers dot com>