But Smalltalk methods are sequential procedures by nature, so having a 
process per object maybe would adress mutual exclusion problem, but will 
not introduce parallelism per se.

Someone has to decide to break execution sequential path into parallel 
paths.

As long as we have 2,3,4 processing units, maybe we can trust programmer 
can use old concurrency model, working with already existing 
Smalltalk::Process objects, we can try hard to make them robust to 
parallelism...

This obviously won't scale to a 1000 or more processing units!

It seems to me that:
- focusing exclusively on solving mutual exclusion problem, sharing 
whole state or none (though I don't understand the value) or partial 
state via some duplication and syncing mecanism (a-la-croquet or 
a-la-spoon-sauce maybe).
- not adressing parallelisation problem (Except early doInParallel: 
proposal).
makes this thread old-concurrency-few-core problem related.

Maybe there is a future for declarative language revival...



PS: for fun, what happens to all-is-object paradigm if each and every 
object has a MessageQueue object? What is the MessageQueue of the 
MessageQueue of ...


Peter William Lount a écrit :
> Hi,
> 
> Sebastian Sastre wrote:
>  
>> hi,
>>
>> What? That just won't work. Think of the memory overhead. 
>>  
>> I don't give credit to unfounded apriorisms. I think it deserves to be 
>> proved that does not work. Anyway let's just assume that may be too 
>> much for state of the art hardware in common computers in year 2007. 
>> What about in 2009? what about in 2012? Remember the attitude you had 
>> saying this now the first day of 2012.
> 
> It's not an unfounded apriorism as you put it.
> 
> Current hardware and technology expected in the next ten years isn't 
> optimized for N hundred thousand or N million threads of execution. 
> Maybe in the future that will be the case.
> 
> The Tile-64 processor is expected to grow to about 4096 processors by 
> pushing the limits of technology beyond what they are today. To reach 
> the levels you are talking about for a current Smalltalk image with 
> millions of objects each having their own thread (or process) isn't 
> going to happen anytime soon.
> 
> I work with real hardware.
> 
> I am open and willing to be pleasantly surprised however.
> 
> 
>> Tying an object instance to a particular process makes no sense. If 
>> you did that you'd likely end up with just as many dead locks and 
>> other concurrency problems since you'd now have message sends to the 
>> object being queued up on the processes input queue. Since processes 
>> could only process on message at a time deadlocks can occur - plus all 
>> kinds of nasty problems resulting from the order of messages in the 
>> queue. (There is a similar nasty problem with the GUI event processing 
>> in VisualAge Smalltalk that leads to very difficult to diagnose and 
>> comprehend concurrency problems). It's a rats maze that's best to avoid.
>>  
>> Besides, in some cases an object with multiple threads could respond 
>> to many messages - literally - at the same time given multiple cores. 
>> Why slow down the system by putting all the messages into a single 
>> queue when you don't have to!?
>> You didn't understand the model I'm talking about.
> 
> That is likely the case.
> 
> 
>> There isn't such a thing as an object with multiple trheads. That does 
>> not exists in this model.
> 
> Ok. I got that.
> 
> 
>> It does exists one process per instance no more no less.
> 
> I did get that. Even if you only do that logically you've got serious 
> problems.
> 
> 
>> I think you're thinking about processes and threads the same way you 
>> know them today.
> 
> I can easily see such a scenario working and also breaking all over the 
> place.
> 
> 
>> Lets see if this helps you to get the idea: Desambiguation: for this 
>> model I'm talking about process not as an OS process but as a VM light 
>> process which we also use to call them threads.
> 
> Ok.
> 
> 
>> So I'm saying that in this model you have only one process per 
>> instance but that process is not a process that can have threads 
>> belonging to it.
> 
> ok.
> 
>> That generates a hell of complexity.
> 
> You lost me there. What complexity?
> 
> 
>> The process I'm saying it's tied to an instance it's more close to the 
>> process word you know from dictionary plus what you know what an 
>> instance is and with the process implemented by a VM that can balance 
>> it across cores.
> 
> I didn't understand. Please restate.
> 
> 
>>  
>> I'm not falling in the pitfall of start trying to parallelize code 
>> automagically. This far from it. In fact I think this is better than 
>> that illusion. Every message is guaranteed by VM to reach it's 
>> destination in guaranteed order. Otherwise will be chaos. And we want 
>> an ordered chaos like the one we have now in a Squeak reified image.
> 
> Yes, squeak is ordered chaos. ;--).
> 
> 
> 
>>  
>> Clarified that I ask why do you think could be deadlocks? and what 
>> other kind of concurrency problems do you think that will this model 
>> suffer?
> 
> 
> If a number of messages are waiting in the input queue of a process that 
> can only process one message at a time since it's not multi-threaded 
> then those messages are BLOCKED while in the thread. Now imagine another 
> process with messages in it's queue that are also BLOCKED since they are 
> waiting in the queue and only one message can be processed at a time. 
> Now imagine that process A and process B each have messages that the 
> other needs before it can proceed but those messages are BLOCKED waiting 
> for processing in the queues.
> 
> This is a real example of what can happen with message queues. The order 
> isn't guaranteed. Simple concurrency solutions often have deadlock 
> scenarios. This can occur when objects must synchronize events or 
> information. As soon as you have multiple threads of execution you've 
> got problems that need solving regardless of the concurrency model in 
> place.
> 
> 
>>  
>> Tying an object's life time to the lifetime of a process doesn't make 
>> sense since there could be references to the object all over the 
>> place. If the process quits the object should still be alive IF there 
>> are still references to it.
>> You'd need to pass around more than references to processes. For if a 
>> process has more than one object you'd not get the resolution you'd 
>> need. No, passing object references around is way better.
>>  
>> Yes of course there will be. In this system a process termination is 
>> one of two things: A) that instance is being reclaimed in a garbage 
>> collection or B) that instance has been written to disk in a kind of 
>> hibernation that can be reified again on demand.  Please refer to my 
>> previous post with subject "One Process Per Instance.." where I talk 
>> more about exacly this.
> 
> If all there is is a one object per process and one process per object - 
> a 1 to 1 mapping then yes gc would work that way but the 1 to 1 mapping 
> isn't likely to ever happen given current and future hardware prospects.
> 
> 
>>  
>> Even if you considered an object as having it's own "logical" process 
>> you'd get into the queuing problems hinted at above.
>>  
>> Which I dont see and I ask your help to understand if you still find 
>> them after the clarifications made about the model.
> 
> See the example above.
> 
> 
>>  
>> Besides objects in Smalltalk are really fine grained. The notion that 
>> each object would have it's own thread would require so much thread 
>> switching that no current processor could handle that. It would also 
>> be a huge waste of resources.
>> And what do you think was going out of the mouths of criticizers of 
>> the initiatives like the park place team had in 1970's making a 
>> Smalltalk with the price of the CPU's and RAM at that time? that VM's 
>> are a smart efficient use of resources?
> 
> That's not really relevant. If you want to build that please go ahead - 
> please don't let me stop you, that's the last thing I'd want. I wish you 
> luck. I get to play with current hardware and hardware that's coming 
> down the pipe such as the Tile-64 or the newest GPUs when they are 
> available to the wider market.
> 
> 
>>  
>> So I copy paste myself: "I don't give credit to unfounded apriorisms. 
>> It deserves to be proven that does not work. Anyway let's just assume 
>> that may be too much for state of the art hardware in common computers 
>> in year 2007. What about in 2009? what about in 2012?"
> 
> Well just get out your calculator. There is an overhead to a thread or 
> process in bytes. Say 512 bytes per thread plus it's stack. There is the 
> number of objects. Say 1 million for a medium to small image. Now 
> multiply those and you get 1/2 gigabyte. Oh, we forgot the stack space 
> and the memory for the objects themselves. Add a multiplier for that, 
> say 8 and you get 4 gigabytes. Oh, wait we forgot that the stack is kind 
> weird since as each message send that isn't to self must be an 
> interprocess or interthread message send you've got some weirdness going 
> on let along all the thread context switching for each message send that 
> occurs. Then you've got to add more for who knows what... the list could 
> go on for quite a bit. It's just mind boggling.
> 
> Simply put current cpu architectures are simply not designed for that 
> approach. Heck they are even highly incompatible with dynamic message 
> passing since they favor static code in terms of optimizations.
> 
>>  
>> Again, one solution does not fit all problems - if it did programming 
>> would be easier.
>>  
>> But programming should have to be easier.
> Yes, I concur, whenever it's possible to do so. But it also shouldn't 
> ignore the hard problems either.
> 
> 
>> Smalltalk made it easier in a lot of aspects.
> 
> Sure I concur. That's why I am working here in this group spending time 
> (is money) on these emails.
> 
>> Listen.. I'm not a naif silver bullet purchaser nor a faithful person. 
>> I'm a critic Smalltalker that thinks he gets the point about OOP and 
>> tries to find solutions to surpass the multicore crisis by getting an 
>> empowered system not consoling itself with a weaker one.
> 
> I do get that about you.
> 
> 
>> Peter please try to forget about how systems are made and think in how 
>> you want to make them.
> 
> I do think about how I want to make them. However to make them I have no 
> choice but to consider how to actually build them using existing 
> technologies and the coming future technologies.
> 
> Currently we have 2-core and 4-core processors as the mainstream with 
> 3-core and 8-core coming to a computer store near you. We have the 
> current crop of GPUs from NVidia that have 128 processing units that can 
> be programmed in a variant of C for some general purpose program tasks 
> using a SIMD (single instruction multiple data) format - very useful for 
> those number crunching applications like graphics, cryptology and 
> numeric analysis to name just a few. We also have the general purpose 
> networked Tile-64 coming - lots of general purpose compute power with an 
> equal amount of scalable networked IO power - very impressive. Intel 
> even has a prototype with 80-cores that is similar. Intel also has it's 
> awesomely impressive Itanium processor with instruction level 
> parallelism as well as multiple cores - just wait till that's a 128 core 
> beastie. Please there is hardware that we likely don't know about or 
> that hasn't been invented yet. Please bring it on!!!
> 
> The bigger problem is that in order to build real systems I need to 
> think about how they are constructed.
> 
> So yes, I want easy parallel computing but it's just a harsh reality 
> that concurrency, synchronization, distributed processing, and other 
> advanced topics are not always easy or possible to simplify as much as 
> we try to want them to be. That is the nature of computers.
> 
> Sorry for being a visionary-realist. Sorry if I've sounded like the 
> critic. I don't mean to be the critic that kills your dreams - if I've 
> done that I apologize. I've simply meant to be the realist who informs 
> the visionary that certain adjustments are needed.
> 
> All the best,
> 
> Peter
> 
> 
> 
> ------------------------------------------------------------------------
> 
>