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How does akka compare to Erlang? [closed]

I've been looking at akka recently and it's pretty impressive. It looks like it has most of the killer features of erlang - location transparency, supervision hierarchies, and more. Are there any features erlang has that akka doesn't?

How, if at all, do Erlang Processes map to Kernel Threads?

Erlang is known for being able to support MANY lightweight processes; it can do this because these are not processes in the traditional sense, or even threads like in P-threads, but threads entirely in user space.

This is well and good (fantastic actually). But how then are Erlang threads executed in parallel in a multicore/multiprocessor environment? Surely they have to somehow be mapped to kernel threads in order to be executed on separate cores?

Assuming that that's the case, how is this done? Are many lightweight processes mapped to a single kernel thread?

Or is there another way around this problem?

What is the difference between a process and a thread

What is the technical difference between a process and a thread? I get the feeling a word like 'process' is over used and there is also hardware and software threads. How about light-weight processes in languages like Erlang? Is there a definitive reason to use one term over the other?

Speed comparison with Project Euler: C vs Python vs Erlang vs Haskell

I have taken Problem #12 from Project Euler as a programming exercise and to compare my (surely not optimal) implementations in C, Python, Erlang and Haskell. In order to get some higher execution times, I search for the first triangle number with more than 1000 divisors instead of 500 as stated in the original problem.

The result is the following:

C:

lorenzo@enzo:~/erlang$ gcc -lm -o euler12.bin euler12.c
lorenzo@enzo:~/erlang$ time ./euler12.bin
842161320

real    0m11.074s
user    0m11.070s
sys 0m0.000s

python:

lorenzo@enzo:~/erlang$ time ./euler12.py 
842161320

real    1m16.632s
user    1m16.370s
sys 0m0.250s

python with pypy:

lorenzo@enzo:~/Downloads/pypy-c-jit-43780-b590cf6de419-linux64/bin$ time ./pypy /home/lorenzo/erlang/euler12.py 
842161320

real    0m13.082s
user    0m13.050s
sys 0m0.020s

erlang:

lorenzo@enzo:~/erlang$ erlc euler12.erl 
lorenzo@enzo:~/erlang$ time erl -s euler12 solve
Erlang R13B03 (erts-5.7.4) [source] [64-bit] [smp:4:4] [rq:4] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.7.4  (abort with ^G)
1> 842161320

real    0m48.259s
user    0m48.070s
sys 0m0.020s

haskell:

lorenzo@enzo:~/erlang$ ghc euler12.hs -o euler12.hsx
[1 of 1] Compiling Main             ( euler12.hs, euler12.o )
Linking euler12.hsx ...
lorenzo@enzo:~/erlang$ time ./euler12.hsx 
842161320

real    2m37.326s
user    2m37.240s
sys 0m0.080s

Summary:

• C: 100%
• python: 692% (118% with pypy)
• erlang: 436% (135% thanks to RichardC)
• haskell: 1421%

I suppose that C has a big advantage as it uses long for the calculations and not arbitrary length integers as the other three. Also it doesn't need to load a runtime first (Do the others?).

Question 1: Do Erlang, Python and Haskell lose speed due to using arbitrary length integers or don't they as long as the values are less than MAXINT?

Question 2: Why is Haskell so slow? Is there a compiler flag that turns off the brakes or is it my implementation? (The latter is quite probable as Haskell is a book with seven seals to me.)

Question 3: Can you offer me some hints how to optimize these implementations without changing the way I determine the factors? Optimization in any way: nicer, faster, more "native" to the language.

EDIT:

Question 4: Do my functional implementations permit LCO (last call optimization, a.k.a tail recursion elimination) and hence avoid adding unnecessary frames onto the call stack?

I really tried to implement the same algorithm as similar as possible in the four languages, although I have to admit that my Haskell and Erlang knowledge is very limited.

Source codes used:

#include <stdio.h>
#include <math.h>

int factorCount (long n)
{
    double square = sqrt (n);
    int isquare = (int) square;
    int count = isquare == square ? -1 : 0;
    long candidate;
    for (candidate = 1; candidate <= isquare; candidate ++)
        if (0 == n % candidate) count += 2;
    return count;
}

int main ()
{
    long triangle = 1;
    int index = 1;
    while (factorCount (triangle) < 1001)
    {
        index ++;
        triangle += index;
    }
    printf ("%ld\n", triangle);
}

#! /usr/bin/env python3.2

import math

def factorCount (n):
    square = math.sqrt (n)
    isquare = int (square)
    count = -1 if isquare == square else 0
    for candidate in range (1, isquare + 1):
        if not n % candidate: count += 2
    return count

triangle = 1
index = 1
while factorCount (triangle) < 1001:
    index += 1
    triangle += index

print (triangle)

-module (euler12).
-compile (export_all).

factorCount (Number) -> factorCount (Number, math:sqrt (Number), 1, 0).

factorCount (_, Sqrt, Candidate, Count) when Candidate > Sqrt -> Count;

factorCount (_, Sqrt, Candidate, Count) when Candidate == Sqrt -> Count + 1;

factorCount (Number, Sqrt, Candidate, Count) ->
    case Number rem Candidate of
        0 -> factorCount (Number, Sqrt, Candidate + 1, Count + 2);
        _ -> factorCount (Number, Sqrt, Candidate + 1, Count)
    end.

nextTriangle (Index, Triangle) ->
    Count = factorCount (Triangle),
    if
        Count > 1000 -> Triangle;
        true -> nextTriangle (Index + 1, Triangle + Index + 1)  
    end.

solve () ->
    io:format ("~p~n", [nextTriangle (1, 1) ] ),
    halt (0).

factorCount number = factorCount' number isquare 1 0 - (fromEnum $ square == fromIntegral isquare)
    where square = sqrt $ fromIntegral number
          isquare = floor square

factorCount' number sqrt candidate count
    | fromIntegral candidate > sqrt = count
    | number `mod` candidate == 0 = factorCount' number sqrt (candidate + 1) (count + 2)
    | otherwise = factorCount' number sqrt (candidate + 1) count

nextTriangle index triangle
    | factorCount triangle > 1000 = triangle
    | otherwise = nextTriangle (index + 1) (triangle + index + 1)

main = print $ nextTriangle 1 1

Where is Erlang used and why? [closed]

I would like to know a list of the most common application/websites/solutions where Erlang is used, successfully or not.

Explaining why it is used into a specific solution instead of others programming languages would be very much appreciated, too.

Listing BAD Erlang case studies (cases in which Erlang is misused) it would be interesting, as well.

What is Erlang written in?

What is Ericsson's implementation of Erlang and Erlang/OTP written and compiled in? Is is assembly, C or Erlang itself?

Update 1: Thanks to DrJokepu. If I understand correctly, Erlang source-to-VM compiler is written in Erlang itself. But the VM is written in C.

Update 2: Hynek-Pichi-Vychodil pointed out a lot of details.

• VM and HW interacting drivers: in C.
• Compiler (to VM) and libraries: in Erlang.
• Extensions: Possible in any language by writing a port or an Erlang node in that language.

convert an integer to a string in Erlang

I know, Erlang strings should be avoided at all costs...

but if I'm not doing that, how do I produce "5" from 5?

in particular, is there anything like io:format("~p",[5]) that would return a formatted string instead of printing to a stream?

Concurrency model: Erlang vs Clojure

We are going to write a concurrent program using Clojure, which is going to extract keywords from a huge amount of incoming mail which will be cross-checked with a database.

One of my teammates has suggested to use Erlang to write this program.

Here I want to note something that I am new to functional programming so I am in a little doubt whether clojure is a good choice for writing this program, or Erlang is more suitable.

Mixing Erlang and Haskell

If you've bought into the functional programming paradigm, the chances are that you like both Erlang and Haskell. Both have purely functional cores and other goodness such as lightweight threads that make them a good fit for a multicore world. But there are some differences too.

Erlang is a commercially proven fault-tolerant language with a mature distribution model. It has a seemingly unique feature in its ability to upgrade its version at runtime via hot code loading. (Way cool!)

Haskell, on the otherhand, has the most sophisticated type system of any mainstream language. (Where I define 'mainstream' to be any language that has a published O'Reilly book so Haskell counts.) Its straightline single threaded performance looks superior to Erlang's and its lightweight threads look even lighter too.

I am trying to put together a development platform for the rest of my coding life and was wondering whether it was possible to mix Erlang and Haskell to achieve a best of breed platform. This question has two parts:

1. I'd like to use Erlang as a kind of fault tolerant MPI to glue GHC runtime instances together. There would be one Erlang process per GHC runtime. If "the impossible happened" and the GHC runtime died, then the Erlang process would detect that somehow and die too. Erlang's hot code loading and distribution features would just continue to work. The GHC runtime could be configured to use just one core, or all cores on the local machine, or any combination in between. Once the Erlang library was written, the rest of the Erlang level code should be purely boilerplate and automatically generated on a per application basis. (Perhaps by a Haskell DSL for example.) How does one achieve at least some of these things?
2. I'd like Erlang and Haskell to be able to share the same garabage collector. (This is a much further out idea than 1.) Languages that run on the JVM and the CLR achieve greater mass by sharing a runtime. I understand there are technical limitations to running Erlang (hot code loading) and Haskell (higher kinded polymorphism) on either the JVM or the CLR. But what about unbundling just the garbage collector? (Sort of the start of a runtime for functional languages.) Allocation would obviously still have to be really fast, so maybe that bit needs to be statically linked in. And there should be some mechansim to distinguish the mutable heap from the immutable heap (incuding lazy write once memory) as GHC needs this. Would it be feasible to modify both HIPE and GHC so that the garbage collectors could share a heap?

Please answer with any experiences (positive or negative), ideas or suggestions. In fact, any feedback (short of straight abuse!) is welcome.

Update

Thanks for all 4 replies to date - each taught me at least one useful thing that I did not know.

Regarding the rest of coding life thing - I included it slightly tongue in cheek to spark debate, but it is actually true. There is a project that I have in mind that I intend to work on until I die, and it needs a stable platform.

In the platform I have proposed above, I would only write Haskell, as the boilerplate Erlang would　be automatically generated. So how long will Haskell last? Well Lisp is still with us and doesn't look like it is going away anytime soon. Haskell is BSD3 open source and has achieved critical mass. If programming itself is still around in 50 years time, I would expect Haskell, or some continuous evolution of Haskell, will still be here.

Update 2 in response to rvirding's post

Agreed - implementing a complete "Erskell/Haslang" universal virtual machine might not be absolutely impossible, but it would certainly be very difficult indeed. Sharing just the garbage collector level as something like a VM, while still difficult, sounds an order of magnitude less difficult to me though. At the garbage collection model, functional languages must have a lot in common - the unbiquity of immutable data (including thunks) and the requirement for very fast allocation. So the fact that commonality is bundled tightly with monolithic VMs seems kind of odd.

VMs do help achieve critical mass. Just look at how 'lite' functional languages like F# and Scala have taken off. Scala may not have the absolute fault tolerance of Erlang, but it offers an escape route for the very many folks who are tied to the JVM.

While having a single heap makes message passing very fast it introduces a number of other problems, mainly that doing GC becomes more difficult as it has to be interactive and globally non-interruptive so you can't use the same simpler algorithms as the per-process heap model.

Absolutely, that makes perfect sense to me. The very smart people on the GHC development team appear to be trying to solve part of the problem with a parallel "stop the world" GC.

http://research.microsoft.com/en-us/um/people/simonpj/papers/parallel-gc/par-gc-ismm08.pdf

(Obviously "stop the world" would not fly for general Erlang given its main use case.) But even in the use cases where "stop the world" is OK, their speedups do not appear to be universal. So I agree with you, it is unlikely that there is a universally best GC, which is the reason I specified in part 1. of my question that

The GHC runtime could be configured to use just one core, or all cores on the local machine, or any combination in between.

In that way, for a given use case, I could, after benchmarking, choose to go the Erlang way, and run one GHC runtime (with a singlethreaded GC) plus one Erlang process per core and let Erlang copy memory between cores for good locality.

Alternatively, on a dual processor machine with 4 cores per processor with good memory bandwidth on the processor, benchmarking might suggest that I run one GHC runtime (with a parallel GC) plus one Erlang process per processor.

In both cases, if Erlang and GHC could share a heap, the sharing would probably be bound to a single OS thread running on a single core somehow. (I am getting out of my depth here, which is why I asked the question.)

I also have another agenda - benchmarking functional languages independently of GC. Often I read of results of benchmarks of OCaml v GHC v Erlang v ... and wonder how much the results are confounded by the different GCs. What if choice of GC could be orthogonal to choice of functional language? How expensive is GC anyway? See this devil advocates blog post

http://john.freml.in/garbage-collection-harmful

by my Lisp friend John Fremlin, which he has, charmingly, given his post title "Automated garbage collection is rubbish". When John claims that GC is slow and hasn't really sped up that much, I would like to be able to counter with some numbers.

Can someone explain the structure of a Pid in Erlang?

Can someone explain the structure of a Pid in Erlang?

Pids looks like this : <A.B.C> , e.g. <0.30.0> , but i would like to know what is the meaning of these three "bits" : A, B and C.

'A' seems to be always 0 on a local node, but this value changes when the Pid's owner is located on another node.

Is it possible to directly send a message on a remote node using only the Pid ? Something like that : <4568.30.0> ! Message , without having to explicitely specify the name of the registered process and the node name ( {proc_name, Node} ! Message ) ?

What libraries can I use to build a GUI with Erlang?

What libraries can I use to build a GUI for an Erlang application? Please one option per answer.

What's a good IDE for Erlang programming?

As far as I know there's Erlang plugin for NetBeans and Eclipse. Which one has the upper hand at the moment?

Are there any other IDE for Erlang which I didnt mention, and how good are they when compare with NetBeans and Eclipse?

What kind of virtual machine is BEAM (the Erlang VM)?

From what I understand a virtual machine falls into two categories either "system virtual machine" or a "process virtual machine". It's kind of fuzzy to me where BEAM lies. Is there another kind of virtual machine I am not aware of?

Setting up an Erlang development environment

I'm interested in looking at Erlang and want to follow the path of least resistance in getting up and running.

At present, I'm planning on installing Erlang R12B-3 and Erlide (Eclipse plugin). This is largely a Google-result-based decision. Initially this will be on a Windows XP system, though I am likely to reproduce the environment on Ubuntu shortly after.

Is there a significantly better choice? Even if it is tied to one platform.

Please share your experiences.

Is there a good, complete tutorial on Erlang parse transforms available?

There are lots of fragments out there detailing bits and pieces of the parse transform process in Erlang, but none I've found offer complete coverage from motivation to execution. Is there a good tutorial I'm missing somewhere and, if so, where can it be found?