# Threads - running something in background

**URL:** <https://www.ruby-forum.com/t/threads-running-something-in-background/174850>\
**Category:** Ruby\
**Created:** [September 3, 2009, 3:47am UTC](https://www.ruby-forum.com/t/threads-running-something-in-background/174850 "2009-09-03T03:47:45Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![akeem](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/54ee81/32.png) [@akeem](https://www.ruby-forum.com/u/akeem)\
**Post date:** [September 3, 2009, 3:47am UTC](https://www.ruby-forum.com/t/threads-running-something-in-background/174850/1 "2009-09-03T03:47:45Z")

</div>

Hey guys,

I’ve been studying Ruby for some weeks now but when it comes to  
threads, I know that I am totally unskilled.

I am trying to build a class which is able to keep updating itself every  
X seconds after being initialized. In general terms it would work like  
this:

* * *

class Threading\_Test  
attr\_accessor :i  
def initialize  
@i = 0  
@j = 0  
neverstop = false

```
t1 = Thread.new do
        while neverstop == false do
          sleep 0.1 #here's the the problem.
          @i = @i + 1
        end
      end

t1.run

puts "I am ready and I keep updating myself. Or not..."

```

## end end

The problem occurs when I try to add this “sleep 0.1” into the thread  
block. The thread only seems to become active when I ask for the @i  
value.

I know that there might be other ways to implement that, but i think  
that it would fit my code better that setting up a Cron task to do so.

Thank you all for the help.

---

<div class="post-metadata">

**Author:** ![akeem](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/54ee81/32.png) [@akeem](https://www.ruby-forum.com/u/akeem)\
**Post date:** [September 3, 2009, 4:49am UTC](https://www.ruby-forum.com/t/threads-running-something-in-background/174850/2 "2009-09-03T04:49:09Z")

</div>

Alex Zunega wrote:

> Hey guys,
> 
> I’ve been studying Ruby for some weeks now but when it comes to  
> threads, I know that I am totally unskilled.
> 
> I am trying to build a class which is able to keep updating itself every  
> X seconds after being initialized. In general terms it would work like  
> this:
> 
> * * *
> 
> class Threading\_Test  
> attr\_accessor :i  
> def initialize  
> @i = 0  
> @j = 0  
> neverstop = false
> 
> ```
> t1 = Thread.new do
> while neverstop == false do
> sleep 0.1 #here's the the problem.
> @i = @i + 1
> end
> end
> 
> t1.run
> 
> puts "I am ready and I keep updating myself. Or not..."
> 
> ```
> 
> ## end end
> 
> The problem occurs when I try to add this “sleep 0.1” into the thread  
> block. The thread only seems to become active when I ask for the @i  
> value.

I’m not sure what you mean. Try this:

class Updater  
attr\_accessor :i

def initialize  
@i = 0

```
Thread.new do
  loop do
    sleep(1)
    @i += 1
    puts "....#{@i}"
  end
end

```

end

end

upd = Updater.new

5.times do  
sleep(2)  
puts upd.i  
end

Here is my output:  
…1  
1  
…2  
…3  
3  
…4  
…5  
5  
…6  
…7  
7  
…8  
…9  
9

---

<div class="post-metadata">

**Author:** ![akeem](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/54ee81/32.png) [@akeem](https://www.ruby-forum.com/u/akeem)\
**Post date:** [September 3, 2009, 4:55am UTC](https://www.ruby-forum.com/t/threads-running-something-in-background/174850/3 "2009-09-03T04:55:36Z")

</div>

Alex Zunega wrote:

> Hey guys,
> 
> I’ve been studying Ruby for some weeks now but when it comes to  
> threads, I know that I am totally unskilled.

Also, you should realize that the @i in the class and the @i in the  
thread are the same variable.  
Therefore, things like this can happen:

class Updater  
attr\_accessor :i

def initialize  
@i = 0

```
Thread.new do
  loop do
    sleep(0.3)
    @i += 1
    puts "....#{@i}"
  end
end

```

end

end

upd = Updater.new

3.times do  
sleep(2)  
puts upd.i

upd.i = 0 #\<-----\*\*\*\*\*\*  
end

–output:–  
…1  
…2  
…3  
…4  
…5  
…6  
6  
…1  
…2  
…3  
…4  
…5  
…6  
…7  
7  
…1  
…2  
…3  
…4  
…5  
…6  
6

---

<div class="post-metadata">

**Author:** ![akeem](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/54ee81/32.png) [@akeem](https://www.ruby-forum.com/u/akeem)\
**Post date:** [September 3, 2009, 5:43am UTC](https://www.ruby-forum.com/t/threads-running-something-in-background/174850/4 "2009-09-03T05:43:05Z")

</div>

7stud – wrote:

> Alex Zunega wrote:
> 
> > Hey guys,
> > 
> > I’ve been studying Ruby for some weeks now but when it comes to  
> > threads, I know that I am totally unskilled.
> 
> Also, you should realize that the @i in the class and the @i in the  
> thread are the same variable.  
> Therefore, things like this can happen:
> 
> class Updater  
> attr\_accessor :i
> 
> def initialize  
> @i = 0
> 
> ```
> Thread.new do
> loop do
> sleep(0.3)
> @i += 1
> puts "....#{@i}"
> end
> end
> 
> ```
> 
> end
> 
> end
> 
> upd = Updater.new
> 
> 3.times do  
> sleep(2)  
> puts upd.i
> 
> upd.i = 0 #\<-----\*\*\*\*\*\*  
> end
> 
> –output:–  
> …1  
> …2  
> …3  
> …4  
> …5  
> …6  
> 6  
> …1  
> …2  
> …3  
> …4  
> …5  
> …6  
> …7  
> 7  
> …1  
> …2  
> …3  
> …4  
> …5  
> …6  
> 6

Hey 7stud,

Thanks for the very prompt answer. I couldn’t make myself clear and I’ll  
try harder this time… 🙂

I’ve just removed two lines from the code you genially sent me. Removing  
these two lines I got the behavior I would like to have. See the code  
and results below:

> > class Updater  
> > attr\_accessor :i

?\> def initialize

> > ```
> > @i = 0
> > 
> > ```

?\> Thread.new do  
?\> loop do  
?\>  
?\> @i += 1

> >

?\> end

> > ```
> > end
> > 
> > ```

?\> end

> >

?\> end  
=\> nil

> > x.i  
> > =\> 213336
> 
> > x.i  
> > =\> 237848
> 
> >

I just want something to time these iteration (one per second, for  
example), and everytime that I insert some “sleep” method, the Updater  
would “sum 1” to @i only when I try to access @i attribute.

What I expect, in other words, is to have an @i very close to the number  
of seconds of the object life, just to prove that it works…

---

<div class="post-metadata">

**Author:** ![akeem](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/54ee81/32.png) [@akeem](https://www.ruby-forum.com/u/akeem)\
**Post date:** [September 3, 2009, 6:41am UTC](https://www.ruby-forum.com/t/threads-running-something-in-background/174850/5 "2009-09-03T06:41:40Z")

</div>

Alex Zunega wrote:

> I just want something to time these iteration (one per second, for  
> example), and everytime that I insert some “sleep” method, the Updater  
> would “sum 1” to @i only when I try to access @i attribute.
> 
> What I expect, in other words, is to have an @i very close to the number  
> of seconds of the object life, just to prove that it works…

You aren’t making any sense. On the one hand, you say that you want @i  
to tell you the number of seconds the object has been “alive”. On the  
other hand, you say you only want to add 1 to @i when you try to access  
@i. Which is it?

---

<div class="post-metadata">

**Author:** ![akeem](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/54ee81/32.png) [@akeem](https://www.ruby-forum.com/u/akeem)\
**Post date:** [September 3, 2009, 9:05am UTC](https://www.ruby-forum.com/t/threads-running-something-in-background/174850/6 "2009-09-03T09:05:14Z")

</div>

I give up.

---

<div class="post-metadata">

**Author:** ![akeem](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/54ee81/32.png) [@akeem](https://www.ruby-forum.com/u/akeem)\
**Post date:** [September 3, 2009, 7:57am UTC](https://www.ruby-forum.com/t/threads-running-something-in-background/174850/7 "2009-09-03T07:57:00Z")

</div>

7stud – wrote:

> Alex Zunega wrote:
> 
> > I just want something to time these iteration (one per second, for  
> > example), and everytime that I insert some “sleep” method, the Updater  
> > would “sum 1” to @i only when I try to access @i attribute.
> > 
> > What I expect, in other words, is to have an @i very close to the number  
> > of seconds of the object life, just to prove that it works…
> 
> You aren’t making any sense. On the one hand, you say that you want @i  
> to tell you the number of seconds the object has been “alive”. On the  
> other hand, you say you only want to add 1 to @i when you try to access  
> @i. Which is it?

Actually, you’re right, I was not clear, but I meant the second one.  
After initialized, 10 seconds later, when retrieving @i value I would  
like to see @i as 10, meaning that for 10 times it updated itself.

---

<div class="post-metadata">

**Author:** ![akeem](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/54ee81/32.png) [@akeem](https://www.ruby-forum.com/u/akeem)\
**Post date:** [September 4, 2009, 3:56am UTC](https://www.ruby-forum.com/t/threads-running-something-in-background/174850/8 "2009-09-04T03:56:20Z")

</div>

7stud’s original Updater class seems to meet the requirements. Are  
you trying to write a class that will perform some work and then sleep  
1.0 seconds and keep a count of the number of iterations it performed?  
Or are you trying to right a class that will perform some work  
exactly once per second? In the first case, your work will not  
generally fire once a second because the work itself will take a non  
zero amount of time. The second case is trickier … maybe this would  
work:

class PeriodicWorker  
def initialize(period = 1.0)  
@period = period  
end

def run  
start = Time.now.to\_f  
while true  
yield  
sleep\_time = (start + @period) - Time.now.to\_f  
sleep(sleep\_time) rescue nil # Punt if the worker took longer  
than @period seconds to run  
start += @period  
end  
end  
end

worker = PeriodicWorker.new

worker.run do  
puts “Time: #{Time.now.to\_f}”  
sleep 0.22  
puts “Finished my work: #{Time.now.to\_f}”  
end

The only issue with this class is if the work takes longer than the  
period, you are creating a spinloop that will suck up 100% of your  
CPU.

-Doug Seifert