# Keep thread in memory

**URL:** <https://www.ruby-forum.com/t/keep-thread-in-memory/162936>\
**Category:** Ruby\
**Created:** [March 15, 2009, 10:38pm UTC](https://www.ruby-forum.com/t/keep-thread-in-memory/162936 "2009-03-15T22:38:07Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![Craig\_Williams](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/8491ac/32.png) [@Craig\_Williams](https://www.ruby-forum.com/u/Craig_Williams)\
**Post date:** [March 15, 2009, 10:38pm UTC](https://www.ruby-forum.com/t/keep-thread-in-memory/162936/1 "2009-03-15T22:38:07Z")

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Hi,

I’m writing a simple UDP listening server. It works great using this

PORT = 1234  
server = UDPSocket.open  
server.bind(“127.0.0.1”, PORT)

server\_thread = Thread.start(server) do |server|  
100.times { #do something }  
end

server\_thread.join

The above was based off some code from the Ruby 1.9 book - I have a  
problem  
now trying to take it a step further.

How do I get the above to run permanently or until some other condition  
besides (100) is reached?

When I run this on my remote server over SSH it works but if I ctrl-z or  
exit ssh, the process seems to be in memory but isn’t actually working.  
I’d  
like to run it and have it go into memory until it is killed and return  
me  
to the ssh command.

I tried leaving off the server\_thread.join but then it just quits. Could  
someone explain exactly what Thread.start is doing here.

thanks!  
-c

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<div class="post-metadata">

**Author:** ![Craig\_Williams](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/8491ac/32.png) [@Craig\_Williams](https://www.ruby-forum.com/u/Craig_Williams)\
**Post date:** [March 15, 2009, 10:52pm UTC](https://www.ruby-forum.com/t/keep-thread-in-memory/162936/2 "2009-03-15T22:52:46Z")

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Craig Williams wrote:

> end  
> exit ssh, the process seems to be in memory but isn’t actually working. I’d  
> like to run it and have it go into memory until it is killed and return me  
> to the ssh command.
> 
> I tried leaving off the server\_thread.join but then it just quits. Could  
> someone explain exactly what Thread.start is doing here.
> 
> thanks!  
> -c

It does exactly what you think it will do. It starts a thread, runs the  
block and exits when the block is completed.  
If you want it to wait around for things to happen, like something being  
fed down a socket, you just need to make a call to an async function,  
like IO.read(server) which will wait around until there is something to  
read.

I can’t explain why your process is still in memory. To me, it should  
have exited and dropped off the face of the planet.

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<div class="post-metadata">

**Author:** ![Craig\_Williams](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/8491ac/32.png) [@Craig\_Williams](https://www.ruby-forum.com/u/Craig_Williams)\
**Post date:** [March 15, 2009, 11:26pm UTC](https://www.ruby-forum.com/t/keep-thread-in-memory/162936/3 "2009-03-15T23:26:10Z")

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On 15.03.2009 22:35, Craig Williams wrote:

> server\_thread = Thread.start(server) do |server|  
> 100.times { #do something }  
> end
> 
> server\_thread.join

First of all, why are you using a thread here? Do you have other work  
that needs to be done concurrently?

> The above was based off some code from the Ruby 1.9 book - I have a problem  
> now trying to take it a step further.
> 
> How do I get the above to run permanently or until some other condition  
> besides (100) is reached?

Depends on the condition. If you want this to run indefinitely you can  
simply do

loop do  
…  
end

> When I run this on my remote server over SSH it works but if I ctrl-z or  
> exit ssh, the process seems to be in memory but isn’t actually working. I’d  
> like to run it and have it go into memory until it is killed and return me  
> to the ssh command.

“Go into memory”??? All programs are executed in memory. What you  
probably rather need is a demon, i.e. a program that continues to work  
even if the terminal gets removed (ssh close).

> I tried leaving off the server\_thread.join but then it just quits. Could  
> someone explain exactly what Thread.start is doing here.

In your example above the thread is completely superfluous since you do  
not do anything concurrently. A plain old infinite loop would do the  
same job. Basically your code is equivalent to

PORT = 1234  
server = UDPSocket.open  
server.bind(“127.0.0.1”, PORT)

100.times { #do something }

Kind regards

robert

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<div class="post-metadata">

**Author:** ![Craig\_Williams](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/8491ac/32.png) [@Craig\_Williams](https://www.ruby-forum.com/u/Craig_Williams)\
**Post date:** [March 15, 2009, 11:33pm UTC](https://www.ruby-forum.com/t/keep-thread-in-memory/162936/4 "2009-03-15T23:33:47Z")

</div>

thanks Robert,

A simple loop…do will work and yes, a daemon is what I want to create.  
I’ll  
look it up and see if I can find some theory around this in Ruby. I  
should  
have said a TSR right 😉

Is it good practice in Ruby to sleep when in an infinite loop? or will  
Ruby  
protect me from that kind of issue?

thanks,

-c

On Sun, Mar 15, 2009 at 6:22 PM, Robert K.

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<div class="post-metadata">

**Author:** ![Craig\_Williams](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/8491ac/32.png) [@Craig\_Williams](https://www.ruby-forum.com/u/Craig_Williams)\
**Post date:** [March 16, 2009, 12:07am UTC](https://www.ruby-forum.com/t/keep-thread-in-memory/162936/5 "2009-03-16T00:07:44Z")

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On Mar 15, 2009, at 10:35 PM, Craig Williams wrote:

> end
> 
> When I run this on my remote server over SSH it works but if I ctrl-  
> z or  
> ctrl-z suspends the current job, and moves it to the background
> 
> thanks!  
> -c

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<div class="post-metadata">

**Author:** ![Craig\_Williams](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/8491ac/32.png) [@Craig\_Williams](https://www.ruby-forum.com/u/Craig_Williams)\
**Post date:** [March 16, 2009, 12:58am UTC](https://www.ruby-forum.com/t/keep-thread-in-memory/162936/6 "2009-03-16T00:58:38Z")

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thanks everyone - I found the Daemons wrapper and a simple loop was well  
simple 🙂 and it works great.

I also know what ctrl-z does now … learning is fun 😉

-c

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<div class="post-metadata">

**Author:** ![Craig\_Williams](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/8491ac/32.png) [@Craig\_Williams](https://www.ruby-forum.com/u/Craig_Williams)\
**Post date:** [March 15, 2009, 11:43pm UTC](https://www.ruby-forum.com/t/keep-thread-in-memory/162936/7 "2009-03-15T23:43:11Z")

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> Is it good practice in Ruby to sleep when in an infinite loop? or will  
> Ruby

Dunno why you would sleep a program when you don’t have to o\_O

sleeping is most useful when working with Threads, though in some cases  
there may be a reason you’d wish to have the program wait for a few  
seconds I suppose.

- Mac