From: Brian Candler <b.candler@...>
Date: 2009-04-30T04:38:43+09:00
Subject: Re: Ruby Interface of Erlang

Brian Candler wrote:
> BTW, I haven't been able to get it to build yet - it's stuck looking for 
> -lei

I found the problem. In configure.rb I had to add "-pthread" to 
--with-ldflags. Without that, mkmf.log was showing the following errors:

"gcc -o conftest -I. -I/usr/local/lib/ruby/1.8/i686-linux -I./src 
-I/usr/lib/erlang/lib/erl_interface-3.5.7/include  -g -O2 conftest.c 
-L'.' -L'/usr/local/lib' -Wl,-R'/usr/local/lib' 
-L'/usr/lib/erlang/lib/erl_interface-3.5.7/lib' 
-Wl,-R'/usr/lib/erlang/lib/erl_interface-3.5.7/lib' -lei -lerl_interface 
-lruby-static -lei  -ldl -lcrypt -lm   -lc"
/usr/lib/erlang/lib/erl_interface-3.5.7/lib/libei.a(ei_pthreads.o): In 
function `__erl_errno_place':
(.text+0x4c): undefined reference to `pthread_once'
/usr/lib/erlang/lib/erl_interface-3.5.7/lib/libei.a(ei_pthreads.o): In 
function `__erl_errno_place':
(.text+0x7a): undefined reference to `pthread_getspecific'
/usr/lib/erlang/lib/erl_interface-3.5.7/lib/libei.a(ei_pthreads.o): In 
function `__erl_errno_place':
(.text+0xa4): undefined reference to `pthread_setspecific'
/usr/lib/erlang/lib/erl_interface-3.5.7/lib/libei.a(ei_pthreads.o): In 
function `__erl_errno_place':
(.text+0xb6): undefined reference to `pthread_getspecific'
/usr/lib/erlang/lib/erl_interface-3.5.7/lib/libei.a(ei_pthreads.o): In 
function `erl_errno_key_alloc':
(.text+0x136): undefined reference to `pthread_key_create'
/usr/lib/erlang/lib/erl_interface-3.5.7/lib/libei.a(ei_pthreads.o): In 
function `ei_m_trylock':
(.text+0x189): undefined reference to `pthread_mutex_trylock'
collect2: ld returned 1 exit status

However, even after successful compilation, it still didn't work due to 
a runtime linker error on "__erl_errno":

irb(main):001:0> require 'erlix'
LoadError: /usr/local/lib/ruby/site_ruby/1.8/i686-linux/erlix.so: 
undefined symbol: __erl_errno - 
/usr/local/lib/ruby/site_ruby/1.8/i686-linux/erlix.so
  from /usr/local/lib/ruby/site_ruby/1.8/i686-linux/erlix.so
  from (irb):1

After poking around header files, I decided that the way to fix this 
was:

$ make clean
$ make CPPFLAGS=-D_REENTRANT

And it happily builds and runs the sample now. I don't know how 
configure.rb should decide for itself whether -D_REENTRANT is needed or 
not.

A few more suggestions:

(1) For converting objects to strings, you should implement a "to_s" 
method, not "puts". Current behaviour is rather un-rubylike:

irb(main):008:0> t=ErlixTuple.new([a1,f,b,a2,i])
=> #<ErlixTuple:0xb7d78d74>
irb(main):009:0> t
=> #<ErlixTuple:0xb7d78d74>
irb(main):010:0> t.puts                 ## unexpected
{atom1,17.000000,#Bin,atom2,101}
=> nil
irb(main):011:0> t.to_s
=> "#<ErlixTuple:0xb7d78d74>"           ## unexpected

This would also allow you to interpolate terms into strings, e.g.

  puts "The response was #{t}"

(2) It would be helpful if ErlixTurple took a variable number of 
arguments, instead of a single array. That would let you write

   ErlixTuple.new(a1,f,b,a2,i)

This wouldn't prevent you from using an array if you like, because Ruby 
provides a 'splat' operator:

   arr = [a1,f,b,a2,i]
   ErlixTuple.new(*arr)

Anyway, keep up the good work - this is looking promising!

Regards,

Brian.
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