[LAD] Atomic Operations

[Tim Blechmann]

>> 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 at klingt.org
http://tim.klingt.org

Which is more musical, a truck passing by a factory or a truck passing
by a music school?
  John Cage

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