Possible ruby bug involving threads and IO

[Lucas Nussbaum]

Hi,

I ran into a problem demonstrated by the following code :

#!/usr/bin/ruby

require 'thread'

Thread::new {
while true do
puts "before read MOTD"
str = IO.read("/etc/motd")
puts "after read MOTD"

puts "before read UPTIME"
str = IO.read("/proc/uptime")
puts "after read UPTIME"
end
}

while true do
end

Ruby hangs on IO.read("/proc/uptime").

Note that it works with linux 2.4 (tested : 2.4.27) but not linux 2.6
(tested : 2.6.9)
It only fails with files on the proc filesystem.

Any ideas ?

Thanks,

 

[William Morgan]

Excerpts from Lucas Nussbaum's mail of 4 Jan 2005 (EST):

Ruby hangs on IO.read("/proc/uptime").

This is probably the same issue described in:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/109668
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/110600

The upshot is that certain files in /proc/ seem to hang on a select()
call, which Ruby uses for I/O within threads. You can do an strace and
watch the difference between doing this from within and from without a
Thread.

My workaround was something along the lines of:
system "cat /proc/#{file} > #{tmpfile}"
f = File.open tmpfile

I don't know that there's a better solution.

 

[Lucas Nussbaum]

Excerpts from Lucas Nussbaum's mail of 4 Jan 2005 (EST):

This is probably the same issue described in:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/109668
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/110600
true

The upshot is that certain files in /proc/ seem to hang on a select()
call, which Ruby uses for I/O within threads. You can do an strace and
watch the difference between doing this from within and from without a
Thread.

My workaround was something along the lines of:
system "cat /proc/#{file} > #{tmpfile}"
f = File.open tmpfile

I don't know that there's a better solution.

IO.popen("/bin/cat /proc/uptime")

But still, that's not very satisfying ...