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  • Canonical pattern reference in Actors programming model.

    - by Bubba88
    Hello! Is there a source, which I could use to learn some of the most used and popular practices regarding Actor-/Agent-oriented programming. My primary concern is about parallelism and distribution limited to the mentioned scheme - Actors, message passing. Should I begin with Erlang documentation or maybe there is any kind of book that describes the most important building blocks when programming Actor-oriented? Thank you! (Most useful examples would be in Scala or F#)

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  • Is F# a poor choice for a functional language

    - by dagda1
    Hi, To me, I think F# is a bad choice due to the fact that it uses threads behind the scenes. To me, threads are too "heavy" due to things like context switching. I can see why Erlang is a good choice because it uses light weight processes. Am I wrong? Cheers Paul

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  • Apache as Reverse Proxy for CouchDB

    - by Overflown
    I'm thinking of a web app that uses CouchDB extensively, to the point where there would be great gains from serving with the native erlang HTTP API as much as possible. Can you configure Apache as a reverse proxy to allow outside GETs to be proxied directly to CouchDB, whereas PUT/POST are sent to the application internal logic (for sanitation, authentication...)? Or is this unwise -- the CouchDB built-in authentication options just seem a little weak for a Web App. Thanks

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  • Is there a suitable replacement for C++, when I would like to write video processing applications?

    - by Nisanio
    Hi I want to write a video editing software, and the "logical" conclusion is that the language I must to use is C++... But I don't like it (sorry c++ fans) I would like to write it with something cool, like Lisp or Haskell or Erlang... But I don't know if the open source implementation of those languages (I don't have money to buy licenses) let me made a competitive software (in the performance area) What do you think? what do you recommend?

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  • Ubuntu 10.04: Unable to Start RabbitMQ Server Post-Installation

    - by Garland W. Binns
    After installing RabbitMQ on Ubuntu 10.04 I receive a failure message that the service was unable to start. Any insight into the issue would be greatly appreciated! Below are contents of startup_log and startup_err. Startup_log: {error_logger,{{2012,7,7},{15,50,31}},"Protocol: ~p: register error: ~p~n",["inet_tcp",{{badmatch,{error,etimedout}},[{inet_tcp_dist,listen,1},{net_kernel,start_protos,4},{net_kernel,start_protos,3},{net_kernel,init_node,2},{net_kernel,init,1},{gen_server,init_it,6},{proc_lib,init_p_do_apply,3}]}]} {error_logger,{{2012,7,7},{15,50,31}},crash_report,[[{initial_call,{net_kernel,init,['Argument__1']}},{pid,<0.20.0>},{registered_name,[]},{error_info,{exit,{error,badarg},[{gen_server,init_it,6},{proc_lib,init_p_do_apply,3}]}},{ancestors,[net_sup,kernel_sup,<0.9.0>]},{messages,[]},{links,[#Port<0.100>,<0.17.0>]},{dictionary,[{longnames,false}]},{trap_exit,true},{status,running},{heap_size,987},{stack_size,24},{reductions,512}],[]]} {error_logger,{{2012,7,7},{15,50,31}},supervisor_report,[{supervisor,{local,net_sup}},{errorContext,start_error},{reason,{'EXIT',nodistribution}},{offender,[{pid,undefined},{name,net_kernel},{mfa,{net_kernel,start_link,[[rabbitmqprelaunch877,shortnames]]}},{restart_type,permanent},{shutdown,2000},{child_type,worker}]}]} {error_logger,{{2012,7,7},{15,50,31}},supervisor_report,[{supervisor,{local,kernel_sup}},{errorContext,start_error},{reason,shutdown},{offender,[{pid,undefined},{name,net_sup},{mfa,{erl_distribution,start_link,[]}},{restart_type,permanent},{shutdown,infinity},{child_type,supervisor}]}]} {error_logger,{{2012,7,7},{15,50,31}},std_info,[{application,kernel},{exited,{shutdown,{kernel,start,[normal,[]]}}},{type,permanent}]} {"Kernel pid terminated",application_controller,"{application_start_failure,kernel,{shutdown,{kernel,start,[normal,[]]}}}"} Startup_err: Crash dump was written to: erl_crash.dump Kernel pid terminated (application_controller) ({application_start_failure,kernel,{shutdown,{kernel,start,[normal,[]]}}})

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  • Installing Yaws server on Ubuntu 12.04 (Using a cloud service)

    - by Lee Torres
    I'm trying to get a Yaws web server working on a cloud service (Amazon AWS). I've compilled and installed a local copy on the server. My problem is that I can't get Yaws to run while running on either port 8000 or port 80. I have the following configuration in yaws.conf: port = 8000 listen = 0.0.0.0 docroot = /home/ubuntu/yaws/www/test dir_listings = true This produces the following successful launch/result: Eshell V5.8.5 (abort with ^G) =INFO REPORT==== 16-Sep-2012::17:21:06 === Yaws: Using config file /home/ubuntu/yaws.conf =INFO REPORT==== 16-Sep-2012::17:21:06 === Ctlfile : /home/ubuntu/.yaws/yaws/default/CTL =INFO REPORT==== 16-Sep-2012::17:21:06 === Yaws: Listening to 0.0.0.0:8000 for <3> virtual servers: - http://domU-12-31-39-0B-1A-F6:8000 under /home/ubuntu/yaws/www/trial - =INFO REPORT==== 16-Sep-2012::17:21:06 === Yaws: Listening to 0.0.0.0:4443 for <1> virtual servers: - When I try to access the the url (http://ec2-72-44-47-235.compute-1.amazonaws.com), it never connects. I've tried using paping to check if port 80 or 8000 is open(http://code.google.com/p/paping/) and I get a "Host can not be resolved" error, so obviously something isn't working. I've also tried setting the yaws.conf so its at Port 80, appearing like this: port = 8000 listen = 0.0.0.0 docroot = /home/ubuntu/yaws/www/test dir_listings = true and I get the following error: =ERROR REPORT==== 16-Sep-2012::17:24:47 === Yaws: Failed to listen 0.0.0.0:80 : {error,eacces} =ERROR REPORT==== 16-Sep-2012::17:24:47 === Can't listen to socket: {error,eacces} =ERROR REPORT==== 16-Sep-2012::17:24:47 === Top proc died, terminate gserv =ERROR REPORT==== 16-Sep-2012::17:24:47 === Top proc died, terminate gserv =INFO REPORT==== 16-Sep-2012::17:24:47 === application: yaws exited: {shutdown,{yaws_app,start,[normal,[]]}} type: permanent {"Kernel pid terminated",application_controller," {application_start_failure,yaws,>>>>>>{shutdown,>{yaws_app,start,[normal,[]]}}}"} I've also opened up the port 80 using iptables. Running sudo iptables -L gives this output: Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT tcp -- ip-192-168-2-0.ec2.internal ip-192-168-2-16.ec2.internal tcp dpt:http ACCEPT tcp -- 0.0.0.0 anywhere tcp dpt:http ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED ACCEPT tcp -- anywhere anywhere tcp dpt:http ACCEPT tcp -- anywhere anywhere tcp dpt:http Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination In addition, I've gone to the security group panel in the Amazon AWS configuration area, and add ports 80, 8000, and 8080 to ip source 0.0.0.0 Please note: if you try to access the URL of the virtual server now, it likely won't connect because I'm not running currently running the yaws daemon. I've tested it when I've run yaws either through yaws or yaws -i Thanks for the patience

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  • Distributed website server redundancy

    - by Keith Lion
    Assume a website infrastructure is very complicated and is fully distributed (probably like most large web companies). Am I right in thinking that although there are all these extra web servers to handle multiple client requests, there is still a single "machine" whereby users must enter? I am guessing this machine will be the one physically associated to the IP address? I ask because I need to know whether, in places where distributed systems exist, there is still a single point of failure- usually the control node or, in this example, the machine connected to the public internet? Surely there cannot be two machines connected to the internet, as they would have to have different IP addresses? This "machine" may not be a server per se, but maybe it is a piece of cisco equipment. I just need to know whether, in the real world, these distributed systems still have a particular section where they depend on the integrity of one electronic device?

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  • not output exception stack trace in EUnit

    - by hpyhacking
    I'm write a test with EUnit, but not anything exception detail output in console. exp_test() -> ?assertEqual(0, 1/0). Run this module:exp_test() in the Erlang Shell output following ** exception error: bad argument in an arithmetic expression in function exp_test:'-exp_test/0-fun-0-'/1 (src/test/eunit/xxx_test.erl, line 8) But in EUnit output following > eunit:test(xxx). > xxx_test: exp_test...*failed* ::badarith EUnit not output anything exception trace info Im trying the verbose config in eunit, but no effect. I want to output some exception detail in eunit test result. Thanks~

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  • Sharing [config] data across modules,functions

    - by williamstw
    I have some configuration data in a config file that I read off disk when the app starts. I need to make that configuration data available to other functions/modules in the application. I started down the path of looking into ets/mnesia to store the data on startup to make it shared among all processes, but then my inner voice cautioned me that there must be a more functional, erlang-y way to do this. The only alternate approach I've come up with so far is setting up a module that has an actor loop that reads the data on startup and responds to messages like {Key, From} and responds by From ! {ok,Value}. Then, I gave up and decided to ask... Thanks, --tim

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  • lists:keyfind problems

    - by dagda1
    Hi, I cannot for the life of me get lists:keyfind to work as I expect in Erlang. I have the following eunit test: should_find_key_test() -> NewList = lists:keystore("key", 1, [], {"key", "value"}), Value = case lists:keyfind("key", 1, NewList) of false -> notfound; {_key, _value} -> _value end, ?debugVal(Value). Whenever I run this test I get the following error message: indextests:should_find_key_test (module 'indextests')...failed ::error:undef in function lists:keyfind/3 called as keyfind("key",1,[{"key","value"}]) in call from indextests:should_find_key_test/0 Can anyone see what I am doing wrong? Is it saying that lists:keyfind no longer exists? Cheers Paul

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  • Maximum open sll connections on Windows

    - by scooterman
    version: erlang R13B Hi all, how can I increase the amount of ssl ports/handles that my network server is able to create on Windows? On linux I was able to successful create about 1000 connections using: -env ERL_MAX_PORTS 80000 -P 268435456 and changing the maximum open fd's using ulimit. On windows apparently there is no effect using the same configuration, and sadly the number of open connections are VERY small (about 30, and it opens 6 handles for each one). I've noticed that the shell starts two other children processes, inet_gethost.exe and ssl_esock.exe. If these are the ones that I have to increase the port count, how do I do that? Thanks,

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  • Why are C, C++, and LISP so prevalent in embedded devices and robots?

    - by David
    It seems that the software language skills most sought for embedded devices and robots are C, C++, and LISP. Why haven't more recent languages made inroads into these applications? For example, Erlang would seem particularly well-suited to robotic applications, since it makes concurrent programming easier and allows hot swapping of code. Python would seem to be useful, if for no other reason than its support of multiple programming paradigms. I'm even surprised that Java hasn't made a foray into general robotic programming. I'm sure one argument would be, "Some newer languages are interpreted, not compiled" - implying that compiled languages are quicker and use fewer computational resources. Is this still the case, in a time when we can put a Java Virtual Machine on a cell phone or a SunSpot? (and isn't LISP interpreted anyway?)

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  • Parse MIME messages

    - by Abhimanyu
    Hi, For my new project which has email module.i need to show all the email information on web.when i m making a call to server i m getting the base64 encoded mime data. after applying base64 decoding technique i m getting the mime data as follows: /*****************Mime data start *******************************/ From [email protected] Tue Jun 23 12:01:02 2009 Date: Tue, 23 Jun 2009 12:01:02 +0530 From: Prashant R Naik <[email protected]> To: [email protected] Subject: This is a test mail Message-ID: <[email protected]> Reply-To: Prashant R Naik <[email protected]> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="ReaqsoxgOBHFXBhH" Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Status: RO Content-Length: 1912 Lines: 52 --ReaqsoxgOBHFXBhH Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Test mail. Initiated by prashant Regards, -- Prashant R Naik Principal Technologist | Symbian & Web2.0 Geodesic Limited | www.geodesic.com Tel: +91-80-66551000 --ReaqsoxgOBHFXBhH Content-Type: image/gif Content-Disposition: attachment; filename="trash.gif" Content-Transfer-Encoding: base64 R0lGODlhEAAQANUoADJ8wTqU2DmR1TqV2DN9wTSBxTWFyTaGyTJ9wTWGyTaKzjmS1TOAxTuV 2DaFyTN8wDiN0jiO0jSAxTeKzjqS1DN8wTqR1TWFyjB4vTOBxTmO0TmS1DaKzTeJzTqV1zSA xDJ8wDqS1TeKzTF4vDF4vTiO0f///zuX2gAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACH5BAEAACgALAAA AAAQABAAAAaDQNRpSCwWhcakcsk8mZ5Qpik5pUKvT2W1uDVWp+BiYNAImAZmz/lcDoQEFoFp QTFtTPKFQLCAREolJiURJhCCJhqAJRMiIhwmjSYdJgqUjQoODgkJJgecBp0mBgYXBx8ZBQxY UAUSDAUACLEPDwgEAAAEIBUEtygkIyMkwMMYw8EjKEEAOw== --ReaqsoxgOBHFXBhH Content-Type: image/jpeg Content-Disposition: attachment; filename="bx.jpg" Content-Transfer-Encoding: base64 /9j/4AAQSkZJRgABAQEASABIAAD/2wBDAAEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEB AQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQH/2wBDAQEBAQEBAQEBAQEBAQEB AQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQH/wAAR CAAUAAoDAREAAhEBAxEB/8QAFQABAQAAAAAAAAAAAAAAAAAAAAn/xAAYEAEAAwEAAAAAAAAA AAAAAAAAGWen5//EABQBAQAAAAAAAAAAAAAAAAAAAAD/xAAUEQEAAAAAAAAAAAAAAAAAAAAA /9oADAMBAAIRAxEAPwCb4AJHym0Vp3PQJTaK07noJHgA/9k= --ReaqsoxgOBHFXBhH Content-Type: image/png Content-Disposition: attachment; filename="day_bg.png" Content-Transfer-Encoding: base64 iVBORw0KGgoAAAANSUhEUgAAAGQAAAApCAYAAADDJIzmAAAABmJLR0QA/wD/AP+gvaeTAAAA CXBIWXMAAAsTAAALEwEAmpwYAAAAB3RJTUUH2AwCCS0kTriU2QAAAB10RVh0Q29tbWVudABD cmVhdGVkIHdpdGggVGhlIEdJTVDvZCVuAAAAXElEQVR42u3bQQEAMAgDMZiqiZtP5AwbfeQk NO/WvPtLMR0TABEQIAICRECACAgQAREQIAICRECACAgQAREQIAICRECACAgQAREQIAICRECA CAgQARGQ7NpPPasFT+0FZPjBRwYAAAAASUVORK5CYII= --ReaqsoxgOBHFXBhH-- /*****************Mime data end *******************************/ now the problem is i have to parse this data and use it in my application.since this data is not a xml so it difficult to parse it (because parsing with some tag is easy).so any one who knows how to parse mime data help be.i m using erlang to parse this data. Thank you in advance

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  • gen_server with a dict vs mnesia table vs ets

    - by pablo
    Hi, I'm building an erlang server. Users sends http requests to the server to update their status. The http request process on the server saves the user status message in memory. Every minute the server sends all messages to a remote server and clear the memory. If a user update his status several times in a minute, the last message overrides the previous one. It is important that between reading all the messages and clearing them no other process will be able to write a status message. What is the best way to implement it? gen_server with a dict. The key will be the userid. dict:store/3 will update or create the status. The gen_server solves the 'transaction' issue. mnesia table with ram_copies. Handle transactions and I don't need to implement a gen_server. Is there too much overhead with this solution? ETS table which is more light weight and have a gen_server. Is it possible to do the transaction in ETS? To lock the table between reading all the messages and clearing them? Thanks

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  • Using RabbitMQ (Java client), is there a way to determine if network connection is closed during con

    - by MItch Branting
    I'm using RabbitMQ on RHEL 5.3 using the Java client. I have 2 nodes (machines). Node1 is consuming messages from a queue on Node2 using the Java helper class QueueingConsumer. QueueingConsumer consumer = new QueueingConsumer(channel); channel.basicConsume("MyQueueOnNode2", noAck, consumer); while (true) { QueueingConsumer.Delivery delivery = consumer.nextDelivery(); ... Process message - delivery.getBody() } If the interface is brought down on Node1 or Node2 (e.g. ifconfig eth1 down), the client (above) never knows the network isn't there anymore. Does RabbitMQ provide some type of configuration on the Java client that can be used to determine if the connection has gone away. Shutting down the RabbitMQ server on Node2 will trigger a ShutdownSignalException, which can be caught and the app can go into a reconnect loop. But bringing down the interface doesn't cause any type of exception to happen, so the code will be waiting forever on consumer.nextDelivery(). I've also tried using the timeout version of this call. e.g. QueueingConsumer consumer = new QueueingConsumer(channel); channel.basicConsume("MyQueueOnNode2", noAck, consumer); int timeout_ms = 30000; while (true) { QueueingConsumer.Delivery delivery = consumer.nextDelivery(timeout_ms); if (delivery == null) { if (channel.isOpen() == false) // Seems to always return true { throw new ShutdownSignalException(); } } else { ... Process message - delivery.getBody() } } but appears that this always returns true (even though the interface is down). I assume registering for the ShutdownListener on the connection will yield the same results, but haven't tried that yet. Is there a way to configure some sort of heartbeat, or do you just have to write custom lease logic (e.g. "I'm here now") in order to get this to work?

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  • Is tcerl for Mnesia production ready? Is there any alternatives?

    - by Sanoj
    I would like to create a scalable web service using Mnesia as database. However Mnesia per default isn't scalable for persistent storgage since it is using Dets (which has a 2GB limit) as backend. I have seen discussions about extending Mnesia with MnesiaEx and use tcerl as backend. It sounds good and have showed good performance. However, I have seen in a talk about Tokyo Cabinet and CouchDB with Mnesia that there are some issues: issues with durability issues with memory leaks issues with crashes Is tcerl + Mnesia really production ready? And is there any other alternatives? How doe´s companies overcome these issues if they use Mnesia in bigger systems? Is there a working solution with Mnesia and Tokyo Tyrant that is working better?

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  • mnesia primary key

    - by maryjanne
    Hi I have two tables one notes and one tag and I want to make the id from notes primary key to use it in the tag table, but I don't know where I do wrong. My notes id is generate from another table counter, with the function dirty_update_counter. My function for the id_notes from tag looks like this: Fun = fun() -> mnesia:write(#tag{ id_note =0}) end, mnesia:transaction(Fun). generate_Oid(TableName) when is_atom(TableName) -> F = fun() -> [Oid] = mnesia:read(tag, TableName, write), NewId = Oid#tag.id_note+1, New = Oid#tag{id_note = NewId}, mnesia:write(New), NewId end, mnesia:transaction(F). insert_n(N) when is_record(N, note) -> F = fun() -> {atomic, Id} = generate_Oid(note), New = N#note{id = Id}, mnesia:write(New), New end, mnesia:transaction(F). find_n(Id) when is_integer(Id) -> {atomic, [N]} = mnesia:transaction(fun() -> mnesia:read({note, Id}) end), N. But this function don't increment my field id_note from the table tag, despite the fact that in my note table, my id field is incremented from counter table. Thanks in advance for any help.

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  • Where are tables in Mnesia located?

    - by Sanoj
    I try to compare Mnesia with more traditional databases. As I understand it tables in Mnesia can be located to: ram_copies - tables are stored in RAM only, so no durability as in ACID. disc_copies - tables are located on disc and a copy is located in RAM, so the table can not be bigger than the available memory? disc_only_copies - tables are located to disc only, so no caching in memory and worse performance? And the size of the table are limited to the size of dets or the table has to be fragmented. So if I want the performance of doing reads from RAM and the durability of writes to disc, then the size of the tables are very limited compared to a traditional RDBMS like MySQL or PostgreSQL. I know that Mnesia aren't meant to replace traditional RDBMS:s, but can it be used as a big RDBMS or do I have to look for another database? The server I will use is a VPS with limited amount of memory, around 512MB, but I want good database performance. Are disc_copies and the other types of tables in Mnesia so limited as I have understood?

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  • Can a CouchDB document update handler get an update conflict?

    - by jhs
    How likely is a revision conflict when using an update handler? Should I concern myself with conflict-handling code when writing a robust update function? As described in Document Update Handlers, CouchDB 0.10 and later allows on-demand server-side document modification. Update handlers can process non-JSON formats; but the other major features are these: An HTTP front-end to arbitrarily complex document modification code Similar code needn't be written for all possible clients—a DRY architecture Execution is faster and less likely to hit a revision conflict I am unclear about the third point. Executing locally, the update handler will run much faster and with lower latency. But in situations with high contention, that does not guarantee a successful update. Or does the update handler guarantee a successful update?

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