otp

These two give identical output: 1> io:format("Hello, world!~n"). Hello, world! ok 2> io:format("Hello, world!\n"). Hello, world! ok Why does io:format support ~n when \n does the same thing? Are there any differences? According to "Programming Erlang", ~n outputs the platform-specific new line sequence ( \n on Unix, \r\n on Windows, etc.). I think \n just writes the \n character, but am not sure. According to io document , The general format of a control sequence is ~F.P.PadModC . So the format must begin with ~ , and character n is one of the control sequences with the definition Writes a

I am currently working on a live media server, which will allow general consumers to send live video to us. In our current environment we've seen broadcasts sent to us with the duration of days, so the idea of being able to fix a bug (or add a feature) without disconnecting users is extremely compelling. However as I was writing code I realized that hot code swapping doesn't make any sense unless I write every process so that all state is always done inside a gen_server, and all external modules that gen_server calls must be as simple as possible. Let's take the following example: -module

What are the main advantages of using a model for concurrency based on processes over one based on threads and in what contexts is the latter appropriate? knutin Fault-tolerance and scalability are the main advantages of using Processes vs. Threads. A system that relies on shared memory or some other kind of technology that is only available when using threads, will be useless when you want to run the system on multiple machines. Sooner or later you will need to communicate between different processes. When using processes you are forced to deal with communication via messages, for example,

I would like to build and deploy an application which has Django as frontend, YAWS ( appmods ) or Mochiweb/Webmachine as a backend and CouchDB as a datastore. Furthermore, I plan to extensively use CouchDB's ability to replicate in order to provide high fault tolerance for the whole application. I tend to think that in order to achieve this, I must create a single OTP release which has YAWS and CouchDB as Erlang/OTP applications. Does this approach seem to be correct? How can I organize YAWS and CouchDB in terms of OTP applications in order to create a solid production setup? Are there any

I have an elixir project with a defined version. How can I access this from within the running application. in mix.exs def project do [app: :my_app, version: "0.0.1"] end I would like to be access this version number in the application so I can add it to the returned message. I looking for something in the env hash like the following __ENV__.version # => 0.0.1 Here's a similar approach to retrieve the version string. It also relies on the :application module, but is maybe a bit more straightforward: {:ok, vsn} = :application.get_key(:my_app, :vsn) List.to_string(vsn) Mix.Project itself

Good day, I have a gen_server process which does some long-running state-updating tasks periodically in handle_info : handle_info(trigger, State) -> NewState = some_long_running_task(), erlang:send_after(?LOOP_TIME, self(), trigger), {noreply, NewState}. But when such task runs, then whole server gets unresponsive and any call to it leads to whole server crash: my_gen_server:status(). ** exception exit: {timeout,{gen_server,call,[my_gen_server,status]}} in function gen_server:call/2 How it is possible to avoid blocking of gen_server ? And when one call my_gen_server:status() at any time, the

I am aware that nodes can be started from the shell. What I am looking for is a way to start a remote node from within a module. I have searched, but have been able to find nothing. Any help is appreciated. A bit more low level that pool is the slave(3) module. Pool builds upon the functionality in slave. Use slave:start to start a new slave. You should probably also specify -rsh ssh on the command-line. So use pool if you need the kind of functionality it offers, if you need something different you can build it yourself out of slave. There's a pool(3) facility: pool can be used to run a set

Is there a limit to the number of processes that can be register globally? Or is this only limited by the memory/ max number of atoms ? Ubuntu 12.04 and Erlang R15B01. Good question! I'd bet on the number of atoms, if you take into account the following. The Efficiency Guide has a section on system limits: Processes The maximum number of simultaneously alive Erlang processes is by default 32768. This limit can be raised up to at most 268435456 processes at startup (see documentation of the system flag +P in the erl(1) documentation). The maximum limit of 268435456 processes will at least on a