Optimising for Concurrency: Comparing the BEAM and JVM virtual machines

Post by di4na » Wed, May 13, 2020, 11:10 PM UTC

hinkley wrote: post #37

di4na wrote: post #35

Earlier quoted context omitted.

I am not sure i understand the problem you are trying to find information about. Maybe explain it a little bit more ? or go ask for it in the elixir forum, people can try to be your librarians there

To an outsider, it seems like the BEAM documentation [and particularly, videos] go out of their way to discuss how process management and IPC communication works and how certain classes of data are managed. They talk about what makes the BEAM the BEAM to exclusion of all other concerns. Prior to finding this document ( http://www.cs-lab.org/historical_beam_instruction_set.html ) I had no idea whether you could actual…

Post by lostcolony » Wed, May 13, 2020, 11:27 PM UTC

chrisseaton wrote: post #48

lostcolony wrote: post #47

Earlier quoted context omitted.

Uh...no. A safepoint is when all threads in the JVM have blocked (which is purely cooperative, and happens during thread transitions), and, importantly, when OS threads running native code still are running , but can't return/respond to the JVM. The JVM doesn't pause those threads. Which is the point. You can't preempt crunching those numbers if it's not within the BEAM. Which might be fine. Or it might not. Making i…

> A safepoint is when all threads in the JVM have blocked And having blocked them, you can then pre-empt them. > You can't preempt crunching those numbers if it's not within the BEAM. I still don't see why sorry. If you had a JIT and you compiled maths intensive code to native code, it could run efficiently in BEAM and still be pre-emptible by having a safepoint in the generated code. How do you think Java is doing o…

Post by trhway » Wed, May 13, 2020, 11:36 PM UTC

vlovich123 wrote: post #12

Traubenfuchs wrote: post #9

> Programming with concurrency primitives is a difficult task because of the challenges created by its shared memory model. I never understood this often repeated point. As junior / mid-level developer I had the privilege to run self written .jar files on government scale systems with more than 50 cores. I used Java thread pools and concurrent data structures to do heavy cross thread caching. It was all pretty simple…

It's fine if you know what you're doing and are the primary maintainer. As someone who's encountered code maintained over a long period of time with lots of people coming and going, concurrency using locks is quite ugly, especially as people cargo cult "better performing" solutions that aren't actually & just add complexity/race conditions. My experience is primarily C/C++ but this is all agnostic to the language.

Post by The_rationalist » Wed, May 13, 2020, 11:43 PM UTC

eggsnbacon1 wrote: post #32

the author leaves out Kotlin which adds support for coroutines on the language level and still compiles to java bytecode. These are not classic continuations because they cannot be cancelled, but they're still very useful and true fibers. There's also the Quasar library that adds fiber support to existing Java projects, but its mostly unmaintained since the maintainers were pulled in to work on Project Loom. Then the…

Post by toast0 » Thu, May 14, 2020, 1:23 AM UTC

lostcolony wrote: post #43

PopeDotNinja wrote: post #36

Earlier quoted context omitted.

Am I correct in saying that functions written in C do not get pre-empted like Erlang functions? If that is true, you could write computationally intense code in C within a BEAM app. But I think this misses the point. Pre-emption is really cool for concurrency abstractions, and the trade off is being less good at single threaded computation. Trying to turn Erlang into something like a Bitcoin miner is kind of like com…

You are correct. It's actually worse than that; as I recall, the internal numerical representations of numbers do not necessarily map to the CPU's (for instance, there is no byte sizing; you have integers and floats, and they can be arbitrarily large). The work to perform that conversion, do the math, and convert back, would almost assuredly make it so that a single calculation takes more time than just doing it with…