# IO redirecting; waitpid

**URL:** <https://www.ruby-forum.com/t/io-redirecting-waitpid/146034>\
**Category:** Ruby\
**Created:** [August 16, 2008, 3:16pm UTC](https://www.ruby-forum.com/t/io-redirecting-waitpid/146034 "2008-08-16T15:16:30Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![tbaustert](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ecae2f/32.png) [@tbaustert](https://www.ruby-forum.com/u/tbaustert)\
**Post date:** [August 16, 2008, 3:16pm UTC](https://www.ruby-forum.com/t/io-redirecting-waitpid/146034/1 "2008-08-16T15:16:30Z")

</div>

Hello.

I have two problems.

First: is there an easy way to redirect data from an incoming IO stream  
to an outgoing IO stream, in a nonblocking way? For example, can you run  
a console program from Ruby program and redirect the program’s output to  
STDOUT in realtime? I know one solution that works, but is there  
anything better?

Thread::new(IO::popen(COMMAND))  
{ |srv|  
until srv.eof?  
print srv.readpartial(1024)  
end  
}

Replacing readpartial with sysread also works, and with read\_nonblock  
works partially.

Second problem: when I use the code above, and at the same time the main  
thread is waiting on Process.waitpid for some other program (not the one  
of which I redirect the output, but some else), then the waiting doesn’t  
terminate correctly. It waits until the process finishes, and then,  
until there is some data available from the process I’m streaming in the  
thread above. And only then the main thread goes on.

I use Windows XP, Ruby 1.8.6.

Here’s a blog entry describing the same problem, with no solution:  
[Ruby (Al2O3::Cr)](http://al2o3-cr.blogspot.com/2008/08/iopopen.html) .

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<div class="post-metadata">

**Author:** ![tbaustert](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ecae2f/32.png) [@tbaustert](https://www.ruby-forum.com/u/tbaustert)\
**Post date:** [August 16, 2008, 5:11pm UTC](https://www.ruby-forum.com/t/io-redirecting-waitpid/146034/2 "2008-08-16T17:11:16Z")

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On Aug 16, 2008, at 7:13 AM, Thomas Bl. wrote:

> STDOUT in realtime? I know one solution that works, but is there  
> works partially.  
> thread above. And only then the main thread goes on.
> 
> I use Windows XP, Ruby 1.8.6.
> 
> Here’s a blog entry describing the same problem, with no solution:  
> [Ruby (Al2O3::Cr)](http://al2o3-cr.blogspot.com/2008/08/iopopen.html) .

you can do it, but not on windows.

a @ [http://codeforpeople.com/](http://codeforpeople.com/)

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<div class="post-metadata">

**Author:** ![tbaustert](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ecae2f/32.png) [@tbaustert](https://www.ruby-forum.com/u/tbaustert)\
**Post date:** [August 17, 2008, 1:05pm UTC](https://www.ruby-forum.com/t/io-redirecting-waitpid/146034/3 "2008-08-17T13:05:49Z")

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On 16.08.2008 17:07, ara.t.howard wrote:

> > a console program from Ruby program and redirect the program’s  
> > output to  
> > STDOUT in realtime? I know one solution that works, but is there  
> > anything better?
> > 
> > Thread::new(IO::popen(COMMAND))  
> > { |srv|  
> > until srv.eof?  
> > print srv.readpartial(1024)  
> > end  
> > }

Yes, use the block form - much safer because streams are properly  
closed:

Thread.new do  
IO.popen COMMAND do |srv|  
buffer = “” # more efficient  
# while srv.readpartial(512, buffer)  
while srv.read(512, buffer)  
STDOUT.write(buffer)  
end  
end  
end

> > I use Windows XP, Ruby 1.8.6.
> > 
> > Here’s a blog entry describing the same problem, with no solution:  
> > [Ruby (Al2O3::Cr)](http://al2o3-cr.blogspot.com/2008/08/iopopen.html) .
> 
> you can do it, but not on windows.

Well, maybe with cygwin.

Kind regards

robert

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<div class="post-metadata">

**Author:** ![tbaustert](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ecae2f/32.png) [@tbaustert](https://www.ruby-forum.com/u/tbaustert)\
**Post date:** [August 17, 2008, 4:51pm UTC](https://www.ruby-forum.com/t/io-redirecting-waitpid/146034/4 "2008-08-17T16:51:16Z")

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On Sat, Aug 16, 2008 at 11:07 AM, ara.t.howard [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> > STDOUT in realtime? I know one solution that works, but is there  
> > works partially.  
> > Here’s a blog entry describing the same problem, with no solution:  
> > [Ruby (Al2O3::Cr)](http://al2o3-cr.blogspot.com/2008/08/iopopen.html) .
> 
> you can do it, but not on windows.

I seem to see this response a lot with regard to ruby’s threading and  
windows.

I’m typically lucky enough to avoid developing for windows. However,  
I am curious if JRuby or 1.9 works around these issues? What about  
IronRuby?

I don’t mean to hijack, but I feel the original poster could benefit  
from answers to these questions also…

Thanks,  
Michael G.

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<div class="post-metadata">

**Author:** ![tbaustert](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ecae2f/32.png) [@tbaustert](https://www.ruby-forum.com/u/tbaustert)\
**Post date:** [August 17, 2008, 4:40pm UTC](https://www.ruby-forum.com/t/io-redirecting-waitpid/146034/5 "2008-08-17T16:40:08Z")

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On 16/08/2008, ara.t.howard [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > a console program from Ruby program and redirect the program’s output to  
> > Replacing readpartial with sysread also works, and with read\_nonblock
> > 
> > Here’s a blog entry describing the same problem, with no solution:  
> > [Ruby (Al2O3::Cr)](http://al2o3-cr.blogspot.com/2008/08/iopopen.html) .
> 
> you can do it, but not on windows.

If Ruby on Windows emulates fork (and there is nothing in the docs  
saying fork would not work on some platforms) you can use fork and  
execute the program normally without popen. The program then inherits  
the standard output fd and you do not have to copy the data to it.

For copying data I haven’t found a working solution on Linux either.

Thanks

Michal

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<div class="post-metadata">

**Author:** ![tbaustert](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ecae2f/32.png) [@tbaustert](https://www.ruby-forum.com/u/tbaustert)\
**Post date:** [August 18, 2008, 3:32am UTC](https://www.ruby-forum.com/t/io-redirecting-waitpid/146034/6 "2008-08-18T03:32:33Z")

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Hi,

At Sat, 16 Aug 2008 22:13:30 +0900,  
Thomas Bl. wrote in [ruby-talk:311482]:

> Second problem: when I use the code above, and at the same time the main  
> thread is waiting on Process.waitpid for some other program (not the one  
> of which I redirect the output, but some else), then the waiting doesn’t  
> terminate correctly. It waits until the process finishes, and then,  
> until there is some data available from the process I’m streaming in the  
> thread above. And only then the main thread goes on.
> 
> I use Windows XP, Ruby 1.8.6.

What’s the exact revision?

It seems not to reproduce with latest 1.8.6 and 1.8.7, but  
could with latest 1.8 branch.

Could you report it to the ITS?  
[http://redmine.ruby-lang.org/projects/ruby/issues/new](http://redmine.ruby-lang.org/projects/ruby/issues/new)