确保epmd开始 [英] Ensure epmd started

问题描述

  {A，B，C} =现在（），
 Nodename = list_to_atom（列表：flatten（io_lib：format（
test-〜b-〜b-〜b @ localhost，[A，B，C]）） 
 {ok，_} = net_kernel：start（[Nodename，shortnames]），
  

只要一个分布式的Erlang节点在上一次在机器上运行，这样epmd仍然在运行，但是在构建服务器上，我不能假设是这样的。

我通过将此添加到我的测试中解决了问题：

  _ = os：cmd（epmd -daemon），
  

但感觉就像一个黑客。在运行 net_kernel：start 之前是否有更好/更好的方式来确保epmd已经启动？

解决方案

不，您不能确保EPMD以更干净的方式开始。

TL; DR

EPMD是一个外部程序，在C 中实现。虽然 net_kernel：start / 1 负责创建 net_sup supervisor ，它实际上并不触发必须明确启动的EPMD守护程序。在 erl 命令中指定 -sname 选项时，我看了一下EPMD的启动方式，惊喜 - 我发现 epmd 程序是通过系统（） C呼叫开始的。

I have an eunit test that generates a unique node name and starts distribution:

{A,B,C} = now(),
Nodename = list_to_atom(lists:flatten(io_lib:format(
    "test-~b-~b-~b@localhost", [A, B, C]))),
{ok, _} = net_kernel:start([Nodename, shortnames]),

This works fine as long as a distributed Erlang node has been running on the machine at some previous time, and thus epmd is still running, but on the build server I can't assume that's the case.

I solved the problem by adding this to my test:

_ = os:cmd("epmd -daemon"),

but it feels like a hack. Is there a better/nicer way to ensure that epmd is started before running net_kernel:start?

解决方案

No, you cannot ensure EPMD is started in a cleaner way.

TL;DR

EPMD is an external program, implemented in C. Whilst net_kernel:start/1 takes care of creating the net_sup supervisor, it does not actually trigger the EPMD daemon, which has to be started explicitely. I had a look at how EPMD is started when the -sname option is specified in the erl command and - surprise, surprise - I discovered that the epmd program is started via a system() C call.

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