Threads: Different behavior under Linux and Windows

Ruby
1

Hi,

I’ve tried the sample code below on Ubuntu (7.04) as well as on a
Windows XP machine.
While under Linux I get the expected result, namely task 1 counting
away, under XP task 1 stalls until I enter something, then runs one loop
and stalls again.
I would have thought that the call to gets in task 2 only blocks task 2,
but not task 1.
Can anybody please explain this to me and more importantly show me a
solution on how to do this so it works under Windows as well?

Thanks in advance,
Armin

require ‘thread’

t1 = Thread.new{
count = 0
loop{
count += 1
sleep 1
print “T1: #{count}\n”
}
}

t2 = Thread.new{
loop{
a = gets
print " T2: a = #{a}\n"
}
}

t1.join
t2.join

2

On Jul 8, 2008, at 8:26 AM, Armin A. wrote:

Can anybody please explain this to me and more importantly show me a
solution on how to do this so it works under Windows as well?

it’s well known - on windows all threads are blocked when the
process is blocked on IO.

a @ http://codeforpeople.com/

3

ara.t.howard schrieb:

On Jul 8, 2008, at 8:26 AM, Armin A. wrote:

Can anybody please explain this to me and more importantly show me a
solution on how to do this so it works under Windows as well?

it’s well known - on windows all threads are blocked when the
process is blocked on IO.

that sure is not because of windows itself… so is there a page
explaining why this is so?

bye Jochen

4

On Jul 8, 2008, at 9:16 AM, Jochen T. wrote:

that sure is not because of windows itself… so is there a page
explaining why this is so?

http://groups.google.com/group/ruby-talk-google/search?group=ruby-talk-google&q=thread+block+windows&qt_g=Search+this+group

also, the pickaxe covers this in the ‘threads and processes’ chapter

a @ http://codeforpeople.com/

5

ara.t.howard wrote:

On Jul 8, 2008, at 9:16 AM, Jochen T. wrote:

that sure is not because of windows itself… so is there a page
explaining why this is so?

http://groups.google.com/group/ruby-talk-google/search?group=ruby-talk-google&q=thread+block+windows&qt_g=Search+this+group

also, the pickaxe covers this in the ‘threads and processes’ chapter

a @ http://codeforpeople.com/

Thanks for your replies Ara.
I tried to find it in the pickaxe (second edition), Chapter 11, but I
couldn’t find anything mentioned about this particular behavior under
Windows.
Also I tried to follow the discussion on google groups but didn’t find a
solution described.

So now I’m stuck. Here’s what I really want to do, maybe someone can
show me a solution to this?
I’d like to write a little terminal application.

  1. Open a serial port
  2. Create a sender task that waits for user input on stdin and sends the
    data out the serial port.
  3. Create a receiver task that waits for data coming from the serial
    port and output it on the screen.

Any suggestions?

Thanks,
Armin

6

ara.t.howard wrote:

to get nonblocking (in a thread) io on windows.

regards.

a @ http://codeforpeople.com/

Thanks again Ara,

I’ll give it a try.

Armin

7

On Jul 8, 2008, at 11:59 AM, Armin A. wrote:

Any suggestions?

Thanks,
Armin

seems like a class case of using select?

if select( [stdin, serial], nil, nil, 0.2 )
…

steve shreeve has had some luck using this paradigm:

require ‘socket’

def socketpair
if RUBY_PLATFORM.include?(“win32”)
listen = TCPServer.new(‘127.0.0.1’, 0)
client = TCPSocket.new(‘127.0.0.1’, listen.addr[1])
server = listen.accept and listen.close
[client, server]
else
UNIXSocket.socketpair
end
end

c,s = socketpair

require ‘win32/process’
info = Process.create(
‘app_name’ => ‘cmd /c “type d:\four_megs.txt & pause”’,
‘startup_info’ => {
‘stdin’ => c,
‘stdout’ => c,
}
)
c.close # needed?

to get nonblocking (in a thread) io on windows.

regards.

a @ http://codeforpeople.com/

8

On Jul 8, 5:19 pm, Jochen T. [email protected] wrote:

that sure is not because of windows itself… so is there a page
explaining why this is so?

No, is not a Windows problem but MRI Ruby Implementation Issue.

Ruby Threads are actually Green Threads (not real threads) so the
interpreter need to loop in them to be able to process them. When IO
is performed in the same thread (since 1.8 is single threaded) it
blocks and stop the green threads to be processed.

This is quite old actually, and been discussed several times here and
ruby-core (search for Io Thread and gets).

There was some changes introduced after p114 (1.8.6) but they needed
to be reverted because they introduced some issues on MinGW
compilation and Drb, which halt the tests (you can also look for that
in ruby-core)

At this time there is no solution for it, except to avoid that
scenario or jump to something like EventMachine to perform that task
(search for EventMachine Console in this forum).

HTH,

9

On Jul 8, 9:00 pm, Daniel B. [email protected] wrote:

It’s actually a bug in MRI. JRuby does not exhibit that behavior, for
example. Park H. posted a patch a short while back that fixes it,
too. That patch has already been applied to Sapphire.

Hey Dan, can you confirm if that patches make Drb tests stall or pass?
similar change introduced in 1.8 (but reverted due this) stall at
least for GCC.

Maybe we can give another shot at this and merge into 1.8 again.

Thank you,

10

On Jul 8, 8:46 am, “ara.t.howard” [email protected] wrote:

On Jul 8, 2008, at 8:26 AM, Armin A. wrote:

Can anybody please explain this to me and more importantly show me a
solution on how to do this so it works under Windows as well?

it’s well known - on windows all threads are blocked when the
process is blocked on IO.

It’s actually a bug in MRI. JRuby does not exhibit that behavior, for
example. Park H. posted a patch a short while back that fixes it,
too. That patch has already been applied to Sapphire.

Regards,

Dan

11

On Wed, Jul 9, 2008 at 5:07 PM, Luis L. [email protected]
wrote:

Also, a recently added spec in Rubyspec is hanging when using threads.
The code that hangs is in 1.8\library\socket\tcpsocket\shared\new.rb.
This is the failing example: http://pastie.org/231434

If you run:

mspec 1.8/library/socket/tcpsocket

You should see it hang.

The offending code is run once for tcpsocket/new_spec.rb and once for
tcpsocket/open_spec.rb. If you run either file individually, no
problems. Do you think this is the same problem?

I’ve tested on these version:

ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32]
ruby 1.8.6 (2008-03-03 patchlevel 114) [i386-mingw32]
ruby 1.8.6 (2008-07-03 patchlevel 265) [i386-mingw32]

Thanks,

Gordon T.

12

On Thu, Jul 10, 2008 at 7:16 AM, Gordon T. [email protected]
wrote:

Also, a recently added spec in Rubyspec is hanging when using threads.

There was a problem with the spec. Sorry for the noise.

Gordon

13

Hi guys,

this problem has been costing me some nerves now. I’ve tried various
things, including EventMachine, with no luck (maybe I did something
wrong).

Anyhow, I finally gave up trying a direct approach and tried a
sub-process/socket approach similar to what Ara suggested.
Here’s something that finally works:

require ‘socket’
require ‘win32/process’

PORT_NUMBER = 12345

CHILD_PROC = ‘ruby -e "’ <<
‘sleep 0.1;’ <<
‘csock = TCPSocket.new(‘localhost’,’ << PORT_NUMBER.to_s <<
‘);’ <<
‘loop{a = gets; csock.print a; exit if a =~ /^exit$/;}’

p = Process.create(:app_name => CHILD_PROC)
#create a green thread that counts every second, to prove that the
parent process is not blocked
t = Thread.new{c = 0; loop{c+=1; puts c;sleep 1}}

l = TCPServer.new(‘localhost’, PORT_NUMBER)
psock = l.accept and l.close
loop{ a = psock.gets; print “Got: #{a}”; exit if exit if a =~ /^exit$/;}

(Note: the example isn’t very useful, all it’s supposed to show is that
the ticker thread is still running while the loop in the parent thread
is blocking on the psock.gets).

I have to admit that I’m not very experienced with either windows
programming or network programming, so while this works I still have
some questions.

  1. Both parent and child process run in the same console window. Who
    “owns” stdin, stdout and stderr? Is there a way that the child process
    could own stdin and the parent stdout and stderr?

  2. Luis/Dan - you mentioned that Park H. has submitted a patch that
    should actually fix the original problem in MRI, but that there were
    some problems with it and therefore it had been reverted. Does anybody
    know whether the latest patchlevel of 1.8.6 (p115 I think) does have the
    problem fixed? If yes, can I download the patch in binary format (so far
    I’ve been using the One-click-installer, I have no experience with
    building ruby from source).

  3. How does fxri circumvent this problem? I can start a ticker thread in
    fxri and it’s happily ticking away. If I try the same thing in irb in a
    console, the ticker stalls until I type stuff.

Thanks,
Armin