81 lines
4.7 KiB
Plaintext
81 lines
4.7 KiB
Plaintext
%hr/
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%p
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layout: site
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author: Torsten
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—
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%p
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Part of what got me started on this project was the intuition that our programming model is in some way broken and so by
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good old programmers logic: you haven’t understood it till you programmed it, I started to walk into the fog.
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%h3#fpgas FPGA’s
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%p
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Don’t ask me why they should be called Field Programmable Gate Arrays, but they have fascinated me for years,
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because off course they offer the “ultimate” in programming. Do away with fixed cpu instruction sets and get the program in silicon. Yeah!
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%p
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But several attempts at learning the black magic have left me only little the wiser.
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Verlilog or VHDL are the languages that make up 80-90% of what is used and they so not object oriented,
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or in any way user friendly. So that has been on the long
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list, until i bumped into
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%a{:href => "http://pshdl.org/"} pshdl
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by way of Karstens
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= succeed "." do
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%a{:href => "https://www.youtube.com/watch?v=Er9luiBa32k"} excellent video on it
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%p
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But what struck me is something he said. That in hardware programming it’s all about getting your design/programm to fit into
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the space you have, and make the timing of the gates work.
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%p
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And i realized that is what is missing from our programming model: time and space. There is no time, as calls happen
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sequentially / always immediately. And there is no space as we have global memory with random access, unlimited by virtual
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memory. But the world we live in is governed by time and space, and that governs the way our brain works.
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%h3#active-objects-vs-threads Active Objects vs threads
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%p
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That is off course not soo new, and the actor model has been created to fix that. And while i haven’t used it much,
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i believe it does, especially in non techie problems. And
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%a{:href => "http://celluloid.io/"} Celluloid
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seems to be a great
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implementation of that idea.
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%p
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Off course Celluloid needs native threads, so you’ll need to run rubinius or jruby. Understandibly. And so we have
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a fix for the problem, if we use celluloid.
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%p
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But it is a fix, it is not part of the system. The system has sequetial calls per thread and threads. Threads are evil as
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i explain (rant about?)
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= succeed "," do
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%a{:href => "/rubyx/threads.html"} here
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%h3#messaging-with-inboxes Messaging with inboxes
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%p
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If you read the rant (it is a little older) you’ll se that it established the problem (shared global memory) but does not propose a solution as such. The solution came from a combination of the rant,
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the
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%a{:href => "/2014/07/17/framing.html"} previous post
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and the fpga physical perspective.
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%p
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A physical view would be that we have a fixed number of object places on the chip (like a cache) and
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as the previous post explains, sending is creating a message (yet another object) and transferring
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control. Now in a physical view control is not in one place like in a cpu. Any gate can switch at
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any cycle, so any object could be “active” at every cycle (without going into any detail about what that means).
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%p
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But it got me thinking how that would be coordinated, because one object doing two things may lead
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to trouble. But one of the Sythesis ideas was
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%a{:href => "http://valerieaurora.org/synthesis/SynthesisOS/ch5.html"} lock free synchronisation
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by use of a test-and-swap primitive.
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%p
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So if every object had an inbox, in a similar way that each object has a class now, we could create
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the message and put it there. And by default we would expect it to be empty, and test that and if
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so put our message there. Otherwise we queue it.
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%p
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From a sender perspective the process is: create a new Message, fill it with data, put it to
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receivers inbox. From a receivers perspective it’s check you inbox, if empty do nothing,
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otherwise do what it says. Do what it says could easily include the ruby rules for finding methods.
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Ie check if your yourself have a method by that name, send to super if not etc.
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%p
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In a fpga setting this would be even nicer, as all lookups could be implemented by associative memory
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and thus happen in one cycle. Though there would be some manager needed to manage which objects are
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on the chip and which could be hoisted off. Nothing more complicated than a virtual memory manager though.
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%p
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The inbox idea represents a solution to the thread problem and has the added benefit of being easy to understand and
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possibly even to implement. It should also make it safe to run several kernel threads, though i prefer the idea of
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only having one or two kernel threads that do exclusively system calls and the rest with green threads that use
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home grown scheduling.
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%p
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This approach also makes one way messaging very natural though one would have to invent a syntax for
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that. And futures should come easy too.
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