From: Simon Strandgaard <0bz63fz3m1qt3001@...>
Date: 2003-05-17T22:04:11+09:00
Subject: select strange behavier

'select' is suppose to watch some file-descriptors and when an event
occurs then an array is returned containing the *affected* file-descriptors.
Problem: the array I get returned seems contain something different!!!

To me it seems like the array contains *non-affected* file-descriptors ???

Am I mistaken?.. notify when theres data to read.. how should I do?


> cat b.rb
require 'stringio'
require 'singleton'

class Redir
        include Singleton
        def initialize
                @out = $stdout
                @error = $stderr
        end
        def set_out(elsewhere)
                @out = elsewhere
        end
        def set_error(elsewhere)
                @error = elsewhere
        end
        def write_out(msg)
                msg = "<out>" + msg + "</out>"
                @out.write(msg)
        end
        def write_error(msg)
                msg = "<err>" + msg + "</err>"
                @error.write(msg)
        end
end

def system(command)
        # todo: stdin
        r1, w1 = IO.pipe # stdout
        r2, w2 = IO.pipe # stderr
        thread = Thread.new do
                loop do
                        puts "waiting"
                        res = select([r1, r2], nil, nil, 0.1)[0]
                        p res
                        if res.include?(r1)
                                unless r1.eof
                                        Redir.instance.write_out r1.read
                                else
                                        puts "r1 not"
                                end
                        end
                        if res.include?(r2)
                                unless r2.eof
                                        Redir.instance.write_error r2.read
                                else
                                        puts "r2 not"
                                end
                        end
                end
        end
        #sleep 0.3    # if we sleep then no output is captured, why ???
        pid = fork do
                r1.close; r2.close
                $defout.reopen(w1); $stdout.reopen(w1); $stderr.reopen(w2)
                exec(command)
                # todo: should I care closing w1+w2 correctly?
        end
        w1.close; w2.close
        Process.waitpid(pid)
        # todo: Wait until the pipes r1+r2 is flushed completly
        sleep 0.5
        r1.close; r2.close
        thread.kill
end

redir = Redir.instance
s = ""
buf = StringIO.new(s, "w")
redir.set_out(buf)
redir.set_error(buf)
system("ruby -e 'puts \"hello\"; system(\"ls main.cpp nonexist\")'")

puts "1"
puts s.split(/\n/).collect { |msg| "OK: "+msg }.join("\n")
puts "2"
>

> ruby -w b.rb
/home/neoneye/stow/ruby18_r2/lib/ruby/1.8/singleton.rb:145: warning: redefine instance
waiting
[#<IO:0x80fcd54>]
waiting
[#<IO:0x80fcd54>, #<IO:0x80fcd18>]
r1 not
waiting
[#<IO:0x80fcd54>, #<IO:0x80fcd18>]
r1 not
r2 not 
  SNIP SNIP SNIP SNIP SNIP SNIP SNIP SNIP
  SNIP   repeats itself many times!  SNIP
  SNIP SNIP SNIP SNIP SNIP SNIP SNIP SNIP
waiting
[#<IO:0x80fcd54>, #<IO:0x80fcd18>]
r1 not
r2 not
waiting
[#<IO:0x80fcd54>, #<IO:0x80fcd18>]
r1 not
r2 not
waiting
[#<IO:0x80fcd54>, #<IO:0x80fcd18>]
r1 not
r2 not
waiting
1
OK: <out>hello
OK: main.cpp
OK: </out><err>ls: nonexist: No such file or directory
OK: </err>
2
>


ruby/machine

> ruby -v
ruby 1.8.0 (2003-03-03) [i386-freebsd5.0]
> uname -a
FreeBSD P350.home 5.0-RELEASE FreeBSD 5.0-RELEASE #0: Thu Jan 16 22:16:53 GMT 2003     root@hollin.btc.adaptec.com:/usr/obj/usr/src/sys/GENERIC  i386
>

--
Simon Strandgaard