# Problem of share variable in function using thread

**URL:** <https://www.ruby-forum.com/t/problem-of-share-variable-in-function-using-thread/191158>\
**Category:** Ruby\
**Created:** [July 6, 2010, 6:01pm UTC](https://www.ruby-forum.com/t/problem-of-share-variable-in-function-using-thread/191158 "2010-07-06T18:01:10Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Nita\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/898d66/32.png) [@Nita\_N](https://www.ruby-forum.com/u/Nita_N)\
**Post date:** [July 6, 2010, 6:01pm UTC](https://www.ruby-forum.com/t/problem-of-share-variable-in-function-using-thread/191158/1 "2010-07-06T18:01:10Z")

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Hi All

I got a little problem when using thread function and variable, let’s  
say this code :

require ‘rubygems’  
require ‘watir’  
require ‘thread’

def testfunc(id)  
total = id + 5  
puts “id #{id} is #{total}”  
end

threads = []  
numberlist = [1, 2, 3]  
for id in numberlist  
threads \<\< Thread.new {testfunc(id)}  
end

threads.each { |aThread| aThread.join }

my output is :  
[sophoah@fedora]$ ruby test.rb  
id 3 is 8  
id 3 is 8  
id 3 is 8

The fact is that I would like this output :  
id 1 is 6  
id 2 is 7  
id 3 is 8

I am suspecting that all variable id, and total are all share among  
all the thread, is that right ? why ? I thought variable in a block  
were not share among variable ? How can I fix this problem ?

Thanks a lot for your help on it,  
Regards  
Nita

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<div class="post-metadata">

**Author:** ![Nita\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/898d66/32.png) [@Nita\_N](https://www.ruby-forum.com/u/Nita_N)\
**Post date:** [July 6, 2010, 6:15pm UTC](https://www.ruby-forum.com/t/problem-of-share-variable-in-function-using-thread/191158/2 "2010-07-06T18:15:18Z")

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> threads = []  
> numberlist = [1, 2, 3]  
> for id in numberlist  
> threads \<\< Thread.new {testfunc(id)}  
> end

…

> The fact is that I would like this output :  
> id 1 is 6  
> id 2 is 7  
> id 3 is 8

what’s happening is that “id” is being changed as it iterates through  
the numberlist.  
So when each thread starts and finally gets around to running  
“testfunc(id)” they all call it with the end value.

The fix is that you can pass a value “through” to the new threads, thus:

Thread.new(id) {|id| testfunc(id) }

Then it will preserve the original value.  
-r

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<div class="post-metadata">

**Author:** ![Nita\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/898d66/32.png) [@Nita\_N](https://www.ruby-forum.com/u/Nita_N)\
**Post date:** [July 6, 2010, 6:17pm UTC](https://www.ruby-forum.com/t/problem-of-share-variable-in-function-using-thread/191158/3 "2010-07-06T18:17:00Z")

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On Tue, Jul 6, 2010 at 6:00 PM, Nita N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> ```
> total = id + 5
> 
> ```
> 
> I am suspecting that all variable id, and total are all share among  
> all the thread, is that right ? why ? I thought variable in a block  
> were not share among variable ? How can I fix this problem ?

Blocks in Ruby are closures, this means that inside the block you pass  
to Thread.new, the variable id is the same.  
The Thread class has a way to avoid this, take a look at the  
constructor:

[http://ruby-doc.org/core/classes/Thread.html#M000437](http://ruby-doc.org/core/classes/Thread.html#M000437)

You can pass parameters to #new and it will pass them to the block.  
You can use this technique to use a variable in the block that is  
different for each thread, like this:

def testfunc(id)  
total = id + 5  
puts “id #{id} is #{total}”  
end

threads = []  
numberlist = [1, 2, 3]  
for id in numberlist  
threads \<\< Thread.new(id) {|my\_id| testfunc(my\_id)}  
end

threads.each { |aThread| aThread.join }

$ ruby threads.rb  
id 1 is 6  
id 2 is 7  
id 3 is 8

Jesus.

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<div class="post-metadata">

**Author:** ![Nita\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/898d66/32.png) [@Nita\_N](https://www.ruby-forum.com/u/Nita_N)\
**Post date:** [July 7, 2010, 5:55pm UTC](https://www.ruby-forum.com/t/problem-of-share-variable-in-function-using-thread/191158/4 "2010-07-07T17:55:35Z")

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On Jul 7, 12:15 am, Jesús Gabriel y Galán [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> > def testfunc(id)  
> > threads.each { |aThread| aThread.join }  
> > id 3 is 8
> 
> numberlist = [1, 2, 3]
> 
> Jesus.

Thanks both of you for your answer.

Regards