From: Matthew Purdy <lists@...>
Date: 2012-11-02T06:06:52+09:00
Subject: streaming stdout with open4 to prevent parent/child buffer lock

i have to fork a process and read a large amount of stdout; however, the
child buffer gets filled up and everything hangs.  how do you read
stdout as stream?

the only way i know how to do this is the following two ways; but both
do not work; how can you get the stdout when the method starts so you
can read stdout as it get written to from the child process?

if not, what is an alternative?

below is two sample scripts to show the use case.

#######################################
open4_test.rb
#######################################

command = 'ruby test_run.rb'

#try it as return
pid, stdin, stdout, stderr = Open4::popen4(command)

while !stdout.eof? do
  puts stdout.gets
end

#try it with a block
status = Open4::popen4(command) do |pid, stdin, stdout, stderr|
  puts stdout.gets if !stdout.eof?
end

###################################


########################
test_run.rb is
########################

(0..100).each do |i|
  puts "helloworld #{i}"
  sleep 1
  puts "goodbye world #{i}"
  sleep 1
end

#######################

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