Re: [LAD] Atomic Operations

>> Actually, his implementation is similar to ringbuffer.c in
>> libjack... and assumes that reading and writing can happen
>> atomically (as was pointed out by someone else) -- which can
>> be managed with single reader / single writer
>> requirement.[a]
>> Unless I've misunderstood the code, ringbuffer.c is /not/
>> using special atomic operations.
>
> Why should a single-reader-single-writer ring-buffer need atomic operations?
>
> The reader increments the read-pointer (which doesn't have to be a pointer)
> last when its finished,

how do you ensure, that the read pointer is incremented _after_ the data
has been written to the output?

> the writer increments the write-pointer last when it
> has written.

likewise, how do you ensure, that the write pointer is incremented
_after_ the data has been written to the ringbuffer?

also, when reading the read/write pointers, you need to ensure, that
they are loaded, before you touch the ringbuffer.

> All other access is read-only. No problems. (At least in my app.)

your code may work on x86, not necessarily on ppc, ia64 ... and then
there is alpha ...
we are not in a world, where assembler instructions are executed one
after the other, but we have out-of-order cpus with speculation and
multi-processor systems with non-shared caches ...

hth, tim

-- 
tim@email-addr-hidden
http://tim.klingt.org
Which is more musical, a truck passing by a factory or a truck passing
by a music school?
  John Cage

_______________________________________________
Linux-audio-dev mailing list
Linux-audio-dev@email-addr-hidden
http://lists.linuxaudio.org/mailman/listinfo/linux-audio-dev