Bartosz Milewski Missing post

[Andrei Alexandrescu]

BCS wrote:
> Reply to Andrei,
> 
>> BCS wrote:
>>
>>> Everything is indicating that shared memory multi-threading is where
>>> it's all going.
>>>
>> That is correct, just that it's 40 years late. Right now everything is
>> indicating that things are moving *away* from shared memory.
>>
>> Andrei
>>
> 
> I'm talking at the ASM level (not the language model level) and as 
> opposed to each thread running in its own totally isolated address space.
> 
> Am I wrong in assuming that most languages use user mode (not kernel 
> mode) shared memory for inter thread communication?

What happens is that memory is less shared as cache hierarchies go 
deeper. It was a great model when there were a couple of processors 
hitting on the same memory because it was close to reality. Cache 
hierarchies reveal the hard reality that memory is shared to a 
decreasing extent and that each processor would rather deal with its own 
memory. Incidentally, message-passing-style protocols are prevalent in 
such architectures even at low level. It follows that message passing is 
not only an attractive model for programming at large, but also a model 
that's closer to machine than memory sharing.


Andrei