# Trouble using puts and getc in different threads

**URL:** <https://www.ruby-forum.com/t/trouble-using-puts-and-getc-in-different-threads/73266>\
**Category:** Ruby\
**Created:** [October 23, 2006, 1:40pm UTC](https://www.ruby-forum.com/t/trouble-using-puts-and-getc-in-different-threads/73266 "2006-10-23T13:40:42Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![mark](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@mark](https://www.ruby-forum.com/u/mark)\
**Post date:** [October 23, 2006, 1:40pm UTC](https://www.ruby-forum.com/t/trouble-using-puts-and-getc-in-different-threads/73266/1 "2006-10-23T13:40:42Z")

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Hi,

I was trying to do a little exercise: Display series of numbers  
(1,2,3,4, 5…etc) in an infinite loop. The program should quit if  
someone hits a specific key (ENTER in my case as the escape key  
requires ugly solutions for non-buffered input). Sounds simple, right?  
Not. I thought this should work:

$done = FALSE

Thread.new do  
STDIN.getc  
$done = TRUE  
end

i = 0  
while !$done  
i = i + 1  
puts i  
end  
puts “We’re done here…”

It doesn’t work. What I see is the loop running until i equals 60 then  
the loop stops! When I press ENTER, the program stops (as expected).

If I replace STDIN.getc by a sleep(3) then the loop runs for 3 seconds  
as expected and the program terminates.

My conclusion: using puts and getc in different threads causes  
trouble. Why is this? How can this be fixed? Should I go about the  
‘loop until key pressed’-problem’ in an entirely different way?

Thanx!  
Mark

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<div class="post-metadata">

**Author:** ![mark](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@mark](https://www.ruby-forum.com/u/mark)\
**Post date:** [October 23, 2006, 2:27pm UTC](https://www.ruby-forum.com/t/trouble-using-puts-and-getc-in-different-threads/73266/2 "2006-10-23T14:27:05Z")

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On 10/23/06, Mark [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Hi,
> 
> I was trying to do a little exercise: Display series of numbers  
> (1,2,3,4, 5…etc) in an infinite loop. The program should quit if  
> someone hits a specific key (ENTER in my case as the escape key  
> requires ugly solutions for non-buffered input). Sounds simple, right?  
> Not. I thought this should work:

Try it on a Unix-like system. It will work. We’ve had several  
discussions  
here about an bad interaction between Ruby threads and system I/O on  
Windows, but I’m not sure anyone has gotten to the bottom of it.

---

<div class="post-metadata">

**Author:** ![mark](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@mark](https://www.ruby-forum.com/u/mark)\
**Post date:** [October 23, 2006, 3:34pm UTC](https://www.ruby-forum.com/t/trouble-using-puts-and-getc-in-different-threads/73266/3 "2006-10-23T15:34:44Z")

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On 10/23/06, Francis C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Try it on a Unix-like system. It will work. We’ve had several discussions  
> here about an bad interaction between Ruby threads and system I/O on  
> Windows, but I’m not sure anyone has gotten to the bottom of it.

Hmm, that was not the answer I was hoping for… And I don’t have the  
luxury of using a linux computer. ☹

Does this mean that is not possible to write a ruby program that  
continuously outputs data on stdout until a key is pressed by the  
user? It sounds so simple.

I found a posting from Nobu Nokada in 2002 saying “Another problem due  
to select(), thread cannot switch while console input.” which  
explaines my code doesn’t work. Must I draw the conclusion that this  
problem still isn’t fixed?

Mark

---

<div class="post-metadata">

**Author:** ![mark](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@mark](https://www.ruby-forum.com/u/mark)\
**Post date:** [October 23, 2006, 6:27pm UTC](https://www.ruby-forum.com/t/trouble-using-puts-and-getc-in-different-threads/73266/4 "2006-10-23T18:27:42Z")

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On 10/23/06, Mark [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> user? It sounds so simple.
> 
> I found a posting from Nobu Nokada in 2002 saying “Another problem due  
> to select(), thread cannot switch while console input.” which  
> explaines my code doesn’t work. Must I draw the conclusion that this  
> problem still isn’t fixed?

if you’re on windows, see [1] thread for a solution, especially [2]  
(using kbhit()) and  
[3] (using select)

[1] [http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/204589](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/204589)  
[2] [http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/204863](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/204863)  
[3] [http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/205002](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/205002)

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<div class="post-metadata">

**Author:** ![mark](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@mark](https://www.ruby-forum.com/u/mark)\
**Post date:** [October 23, 2006, 7:12pm UTC](https://www.ruby-forum.com/t/trouble-using-puts-and-getc-in-different-threads/73266/5 "2006-10-23T19:12:26Z")

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I am on a windows machine, and oddly enough I ran it the code. it went  
to 59 then when I hit enter, it printed 60 We’re done here …

Is that what it was supposed to do?

---

<div class="post-metadata">

**Author:** ![mark](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@mark](https://www.ruby-forum.com/u/mark)\
**Post date:** [October 23, 2006, 6:43pm UTC](https://www.ruby-forum.com/t/trouble-using-puts-and-getc-in-different-threads/73266/6 "2006-10-23T18:43:54Z")

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On 10/23/06, Jan S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> if you’re on windows, see [1] thread for a solution, especially [2]  
> (using kbhit()) and  
> [3] (using select)
> 
> [1] [http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/204589](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/204589)  
> [2] [http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/204863](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/204863)  
> [3] [http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/205002](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/205002)

I’m still wondering what the problem with #getc is. Is it possible that  
the  
way Ruby implements it is not interruptible in Windows, so Ruby can’t  
run  
the thread scheduler around it?

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<div class="post-metadata">

**Author:** ![mark](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@mark](https://www.ruby-forum.com/u/mark)\
**Post date:** [October 23, 2006, 9:36pm UTC](https://www.ruby-forum.com/t/trouble-using-puts-and-getc-in-different-threads/73266/7 "2006-10-23T21:36:37Z")

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Jeremy W. wrote:

> I am on a windows machine, and oddly enough I ran it the code. it went  
> to 59 then when I hit enter, it printed 60 We’re done here …
> 
> Is that what it was supposed to do?

Uh no. I expect the loop to run until I press Enter and not stop before  
that.

Francis & Jan thanks.

Maybe the problem has to do with the fact that input from STDIN is  
echoed. This requires using STDOUT. Maybe STDIN’s thread locks STDOUT?  
But I’m also guessing that other much more knowledgeable people than I  
have had thoughts about this. I’m just having trouble finding those  
posts.

As I’m not going to be writing lots of interactive console applications,  
I’m not going to put more effort into this. It’s clear to me that this  
is a bug in Ruby’s implementation for windows.

Mark