Multy-core CPUs

On 10/25/07, Peter William Lount [hidden email] wrote:
  

 What are they?
    

Here.  Again.  http://sixtyk.blogspot.com/2007/05/threading.html

  

 Sure, one only has to search the internet for "concurrency" and one sees a
wide range of problems and potential solutions. Look at the Little Book of
Semaphores for a breathtaking look at a few of the many possible solutions
to various problems. Open your eyes to the wider horizon.
    

Open my eyes to the wider horizon of yesterday?  I've seen it.  It's
complicated.  I prefer to look at tomorrow.
  

 I never said you stated that explicitly - I'd have to check all your
postings to find that out. It's implied by what you are saying in many of
your postings. At least that is the impression that I'm getting from your
writing. You've certainly not acknowledged the opposite.
    

I really believe that over-all your intentions are good, but this
seems downright dishonest.  Either that are you simply don't read what
I write.  I have told you *every single time* you brought up this
charge that I don't think it will solve all cases.

  

Ok, we're getting no where with this.  I apologized to the list for
what this thread has turned into, and I'll try to do a better job
staying out of this sort of pointless "nu uh", "uh hu!", "nu uh!"
discussions in the future.  (if I start it again just warn me!  It's a
bit of a weakness of mine).
  

---

De: [hidden email] [mailto:[hidden email]] En nombre de Peter William Lount
Enviado el: Jueves, 25 de Octubre de 2007 16:29
Para: The general-purpose Squeak developers list
Asunto: Re: Multy-core CPUs

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. 

Peter.. Peter.. you have to fight a little harder to that demon. Look I asked you to read my previous post with subject "One Process Per Instance" where I taked the time (so money) of explainly as didactic as I can how *your* millon object example could be managed in a system like the one I'm speculating with. So please, please Peter, I ask you not to make repeat myself go read it and make your statements there if you found them. As I already said I think the experiences you are sharing in this matter are precious so discussion gets just richer.

 

 

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.  

 

So I ask you kindly if you can read my previus emails where I where I have taken the job of expresing my exploratory thoughts until reached this model and the speculation about the existence of this model (consequences).

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. 

 

If you have read where I talk about how to manage with this model N millon objects with limited hardware and you still found problems please be my guest to inform me here because I want to know that as soon as possible.

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. 

 

Why? 

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?
 

Does not matter is other model not the one I'm speculating. (probably one you have imagined before clarifiying the 1:1 object process thing) 

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 restates that N times in my previus emails being too long. To give you a clue it's about the double nature I'm saying the object has. An amalgam between object and process. It's conceptual indissociability. More on those previus emails. 

 

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. 

 But that can happen right now if you give a bad use of process in a current Smalltalk. I don't want to solve deadlocks for anybody using parallelism badly. I just want a Smalltalk that works like todays but balancing cpu load across cores and scaling to an arbitrary number of them. All this trhead it's about that.

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. 

 But Peter don't lower your guard on that so easy! we know techniques to administer resources like navegating 10 thousand instances at the time a 10 gigas image of 10 million objects! don't shoot hope before it borns! I talk some details I've imagined about this in my "One Process Per Instance" post.

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.
 

We all have to use cheap hardware. Please (re)think about what I said about administering hardware resources over this model. 

 

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. 
 

I just can't beleive we really can't find clever ways of adminiter resources to the point in which this becomes acceptable. 

 
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. 

 Yes that happens with machines based on mathematic models like the boolean model. It injects an inpedance mismatch between the conceptual modeling and the virtual modeling. 

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

 Please take your time to think about what I've stated of administering resources being possible to manage load of millions of instances by a swarm of a few at the time. And don't be sorry of anything. I love criticism. Our culture need tons of criticism to be stronger. It's the only way we can unistall deprecated or obsolete ideas. You are helping here. If I really dreaming an this don't work I want that dream to be kill now so I can spend my time in something better. That helps.

 By  now this model it's just getting stronger. Please try to get it down !!!   :)))

 

    cheers,

 

Sebastian 

Hi Peter,

 

My response here is not formatted as I would wish, but is the imit of my current technology.

I work on SqueakElib, and though I am certainly no expert on E, I am somewhat familiar with it's design and implementation.  That said, a comment you made caught my eye...

 

> ----- Original Message ----
> From: Peter William Lount [hidden email]
>

> 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.

Messages don't get blocked, when they are queued for the Vat (thread/process) to service them.  They do get queued when they are sent to a Promise, but it does not affect the Vat.  When the Promise resolves, the messages are forwarded to the Vat for processing, in order, so partial msg ordering is maintained. 

 

Msg ordering is partial because of this case: object a in Vat A, object b in Vat B, and object c in Vat C are intercommunicating.  Both b and c have references to a.   At time t1, b sends msg m1 to a, at time t2, c sends msg m2 to a, but there is higher network latency for b, so m2 gets to a at t3 and m1 gets to a at t4 and they are out of order from the remote invocation order.

 

I hope this helps.  Read more about Elib.

 

cheers,

Rob

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. 

Peter.. Peter.. you have to fight a little harder to that demon. Look I asked you to read my previous post with subject "One Process Per Instance" where I taked the time (so money) of explainly as didactic as I can how *your* millon object example could be managed in a system like the one I'm speculating with. So please, please Peter, I ask you not to make repeat myself go read it and make your statements there if you found them. As I already said I think the experiences you are sharing in this matter are precious so discussion gets just richer.

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.  

 

So I ask you kindly if you can read my previus emails where I where I have taken the job of expresing my exploratory thoughts until reached this model and the speculation about the existence of this model (consequences).

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. 

 

If you have read where I talk about how to manage with this model N millon objects with limited hardware and you still found problems please be my guest to inform me here because I want to know that as soon as possible.

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. 

 

Why? 

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?
 

Does not matter is other model not the one I'm speculating. (probably one you have imagined before clarifiying the 1:1 object process thing)

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 restates that N times in my previus emails being too long. To give you a clue it's about the double nature I'm saying the object has. An amalgam between object and process. It's conceptual indissociability. More on those previus emails.

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. 

 But that can happen right now if you give a bad use of process in a current Smalltalk. I don't want to solve deadlocks for anybody using parallelism badly. I just want a Smalltalk that works like todays but balancing cpu load across cores and scaling to an arbitrary number of them. All this trhead it's about that.

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. 

 But Peter don't lower your guard on that so easy! we know techniques to administer resources like navegating 10 thousand instances at the time a 10 gigas image of 10 million objects! don't shoot hope before it borns! I talk some details I've imagined about this in my "One Process Per Instance" post.

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.
 

We all have to use cheap hardware. Please (re)think about what I said about administering hardware resources over this model.

 

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. 
 

I just can't beleive we really can't find clever ways of adminiter resources to the point in which this becomes acceptable.

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. 

 Yes that happens with machines based on mathematic models like the boolean model. It injects an inpedance mismatch between the conceptual modeling and the virtual modeling.

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

 Please take your time to think about what I've stated of administering resources being possible to manage load of millions of instances by a swarm of a few at the time. And don't be sorry of anything. I love criticism. Our culture need tons of criticism to be stronger. It's the only way we can unistall deprecated or obsolete ideas. You are helping here. If I really dreaming an this don't work I want that
dream to be kill now so I can spend my time in something better. That helps.

 By  now this model it's just getting stronger. Please try to get it down !!!   :)))

When a message is sitting in an inbound queue on a process waiting for that process to do get to it it is in essence blocked until it gets processed. If the process is only processing one inbound message at once it is possible for a dead lock to occur when multiple processes are in a similar situation with each other. Both processes waiting for the message that would let them continue which is sitting blocked on the other's queue. That's all. Classic deadlock case.

Hi,


 ... 

I recall a counter example of the million objects was to split the data objects into 10,000 chunks. However, that's a different problem not the one that I have to deal with.

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.  

 

So I ask you kindly if you can read my previus emails where I where I have taken the job of expresing my exploratory thoughts until reached this model and the speculation about the existence of this model (consequences).

There are so many emails in this thread please link to the emails you'd like me to reread. Thanks very much.

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. 

 

If you have read where I talk about how to manage with this model N millon objects with limited hardware and you still found problems please be my guest to inform me here because I want to know that as soon as possible.

Yes, I know it's possible for systems like Erlang to have 100,000 virtual processes, aka lightweight threads, that can be in one real native operating system process or across many native processes.

Are you saying that you've figured out how to do that with millions of processes?

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. 

 

Why? 

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?
 

Does not matter is other model not the one I'm speculating. (probably one you have imagined before clarifiying the 1:1 object process thing)

Alan Kay's original work suggested that each object had a process. There is the logical view and the idealized view. Then there is the concrete and how to implement things. How one explains things to end users is often with the idealized view. How one implements is more often with something that isn't quite the idea.

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 restates that N times in my previus emails being too long. To give you a clue it's about the double nature I'm saying the object has. An amalgam between object and process. It's conceptual indissociability. More on those previus emails.

Alright I'll have to reread the entire thread since no one wants to clearly state their pov in one email as I attempt to do out of courtesy. I don't have time to reread the entire thread today though. (That's why it is a courtesy to repost - it saves your readers time).

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. 

 But that can happen right now if you give a bad use of process in a current Smalltalk. I don't want to solve deadlocks for anybody using parallelism badly. I just want a Smalltalk that works like todays but balancing cpu load across cores and scaling to an arbitrary number of them. All this trhead it's about that.

Yes it can happen now. That's why it's important to actually learn concurrency control techniques. Books like the Little Book of Semaphores can help with that learning process.

The point is that a number of people in this thread are proposing solutions that seem to claim that these problems magically go away in some utopian manner with process-based concurrency. All I'm pointing out is that there isn't a silver bullet or concurrency utopia and now I'm getting flack for pointing out that non-ignorable reality. So be it. Those that push ahead are often the ones with many arrows in their back.

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. 

 But Peter don't lower your guard on that so easy! we know techniques to administer resources like navegating 10 thousand instances at the time a 10 gigas image of 10 million objects! don't shoot hope before it borns! I talk some details I've imagined about this in my "One Process Per Instance" post.

Well then you must have a radically different meaning of 1 to 1 object to process mapping than I have or a radically different implementation that I've understood from your writings. If you can make it work that is all the proof that you need, isn't it!?

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.
 

We all have to use cheap hardware. Please (re)think about what I said about administering hardware resources over this model.

 

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. 
 

I just can't beleive we really can't find clever ways of adminiter resources to the point in which this becomes acceptable.

Each thread needs a stack, a stored set of registers. That's at least two four kilobyte memory pages (one for the stack and one for the registers) with current hardware assuming your thread is mapped to a real processor thread of execution at some point. The two pages are there so that you can have the processor detect if the stack grows beyond it's four kilobyte page. Now you could pack them into one page when it's not being executed but that would increase your context switch time to pack and unpack. If you avoid that and simply use the same page for both then you're risking having your stack overwrite memory used for the process/thread which would be unsafe multi-threading.

Maybe some hardware designers will figure it out.

However, there is still the worst pitfall of the 1 to 1 mapping of process to object: that is the overhead of each message send to another object would require a thread context switch! That's is inescapably huge.

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. 

 Yes that happens with machines based on mathematic models like the boolean model. It injects an inpedance mismatch between the conceptual modeling and the virtual modeling.

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

 Please take your time to think about what I've stated of administering resources being possible to manage load of millions of instances by a swarm of a few at the time. And don't be sorry of anything. I love criticism. Our culture need tons of criticism to be stronger. It's the only way we can unistall deprecated or obsolete ideas. You are helping here. If I really dreaming an this don't work I want that
dream to be kill now so I can spend my time in something better. That helps.

Well having loads of millions of instances managed by a swarm of them at once is what I was assuming. In fact Linux does this (well for thousands not millions anyway). It turns out that Intel's X86/IA32 architecture can only handle 4096 threads in hardware. What Linux did was virtualize them so that only one hardware thread was used for the active thread (per core I would assume). This allowed Linux to avoid the glass ceiling of 4096 threads. However, there are limits due to the overhead of context switching time and the overhead of space that each thread - even with a minimal stack as would be the case with the model you are proposing might have. It's just too onerous for practical use.

Unless you are doing something radically different that I don't understand that is.

 By  now this model it's just getting stronger. Please try to get it down !!!   :)))

I though I crushed it already!!! ;--)

Certainly until you can provide a means for it to handle the one million data objects across 10,000 processes with edits going to the 10,000 processes plus partial object graph seeding (and any object on demand) to them and end up with one and a half million output objects with the total number of interconnections increased by 70% I'll consider it crushed. ;--)

Forward to the future - to infinity and beyond with real hardware!

Cheers,

Peter

On Wed, Oct 24, 2007 at 11:12:13PM -0700, Peter William Lount wrote:
  

An excellent book for learning the ins and outs of concurrency control - 
and most importantly the common mistakes - is the free PDF book, "The 
Little Book of Semaphores",  by Allen B. Downey and his students: 
http://www.greenteapress.com/semaphores/downey05semaphores.pdf.
    

Peter,
Thanks for this reference.
Dave



  

On Wed, Oct 24, 2007 at 11:12:13PM -0700, Peter William Lount wrote:
  

An excellent book for learning the ins and outs of concurrency control - 
and most importantly the common mistakes - is the free PDF book, "The 
Little Book of Semaphores",  by Allen B. Downey and his students: 
http://www.greenteapress.com/semaphores/downey05semaphores.pdf.
    

Peter,
Thanks for this reference.
Dave



  

On Wed, Oct 24, 2007 at 11:12:13PM -0700, Peter William Lount wrote:
  

An excellent book for learning the ins and outs of concurrency control - 
and most importantly the common mistakes - is the free PDF book, "The 
Little Book of Semaphores",  by Allen B. Downey and his students: 
http://www.greenteapress.com/semaphores/downey05semaphores.pdf.
    

Peter,
Thanks for this reference.
Dave