From: Robert Klemme <shortcutter@...>
Date: 2008-08-07T17:04:31+09:00
Subject: Re: Threaded IO trouble

2008/8/6 Michal Suchanek <hramrach@centrum.cz>:
> On 06/08/2008, Michal Suchanek <hramrach@centrum.cz> wrote:
>> Hello
>>
>>  I do not understand the internals of Ruby IO but what I get here looks
>>  really awful.
>>
>>  I am interfacing an application that processes lines of text and
>>  buffers part of the output until EOF (or EOF tag). I thought using an
>>  additional thread would be the right thing to do in this case: one
>>  thread writes stuff, and as the application starts to output stuff
>>  another thread wakes up to read it.
>>
>>  There are two problems here:
>>
>>  1) only reading inside the separate thread is possible, writing causes
>>  stdin to be read into the program
>>
>>  2) reading inside the thread produces deadlocks
>>
>>  Attaching the files required to reproduce both failures.
>>
>>  =================== mock.rb ===================
>>  buf=[]
>>  while l=gets
>>   buf << l
>>   puts buf.shift if buf.length >3
>>  end
> Actually the mockup misses a line here:
>
>  while l = buf.shift do puts l end

And it misses another line at the beginning:

$defout.sync = true

:-)

With that change for me this works as expected:

10:04:42 Temp$ ./ttest.rb
1218096292.04: main      : 0
1218096293.07: main      : 1
1218096297.08: main      : 2
1218096298.08: main      : 3
1218096298.08: reader    : 0
1218096303.08: main      : 4
1218096303.08: reader    : 1
1218096306.09: reader    : 2
1218096306.09: reader    : 3
1218096306.09: reader    : 4
10:05:06 Temp$ cat ttest.rb
#!/bin/env ruby

def log(m)
  t = Thread.current
  printf "%10.2f: %-10s: %s\n",
    Time.now,
    t[:label] || t.inspect,
    m
end

Thread.current[:label] = "main"

IO.popen "./mock.rb", "r+" do |io|
  io.sync = true

  t = Thread.new do
    Thread.current[:label] = "reader"
    io.each do |line|
      log line.chomp
    end
  end

  5.times do |i|
    log i
    io.puts i
    sleep(1 + rand(5))
  end

  io.close_write
  t.join
end
10:05:08 Temp$

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end