Asp Forum - a loop in a thread... very greedy

Abraham Tio

12/31/2007 3:53:00 AM

need a class(we'll call it a 'simulator' since that's what i'm
attempting to write) to run a loop.
need that loop to stop when asked to, such as when the user that started
it clicks a button to stop it.

i write java that does this sort of thing all the time.
HOWEVER, when i try it in ruby, only bad things happen.

check this out:

***start r.rb***
class Simulator
attr_accessor :running
attr_accessor :sim_thread
def start
running = true;
puts "starting simulator..."
sim_thread= Thread.new(){
puts "sim thread started"
while(running)
300000.times do |x|
x+=1
end
puts 'did a buncha stuff a simulator might do'
Thread.pass
end
puts "sim thread stopped"
}
sim_thread.join
sim_thread
end
def stop
puts "stopping simulator..."
running = false
end
end
Thread.abort_on_exception = true
simulator = Simulator.new
thread = simulator.start
puts "started simulator, now we stop it.."
simulator.stop
***end r.rb***

i get no exceptions in the thread.
the output:
starting simulator...
sim thread started
did a buncha stuff a simulator might do
did a buncha stuff a simulator might do
did a buncha stuff a simulator might do

this line never executes:

puts "started simulator, now we stop it.."

why does ruby not leave the thread lone to do its thing,
and do other things ?

instead, it seems to get stuck in the while loop, as if i didn't put it
in a separate thread.

any help much appreciated, thanks.
--
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5 Answers

Gary Wright

12/31/2007 3:59:00 AM

On Dec 30, 2007, at 10:52 PM, Abraham Tio wrote:
>
> sim_thread.join
>

You're explicitly asking the main thread to let
the sim_thread run to completion. Don't join
with another thread if you don't want to wait
for it to exit.

Gary Wright

Marcin Raczkowski

12/31/2007 4:44:00 AM

> why does ruby not leave the thread lone to do its thing,
> and do other things ?
it does ... usually, but since you're explicitly joining it, it'll wait
in start method untill thread finishes

>
> instead, it seems to get stuck in the while loop, as if i didn't put it
> in a separate thread.
You did, and then you turned multi threaded application into single
threaded one

>
> any help much appreciated, thanks.
remove join. read documentation (as java user you should be used to it)

Steve Ross

12/31/2007 5:12:00 AM

On Dec 30, 2007, at 7:52 PM, Abraham Tio wrote:

> Thread.abort_on_exception = true
> simulator = Simulator.new
> thread = simulator.start
> puts "started simulator, now we stop it.."
> simulator.stop

Others have pointed out not to use join. Of course, once you remove
join, the start and stop methods are invoked one right after another,
so you must put a sleep(n) between the two to observe the child thread
running independent of the main thread.

Ezra Zygmuntowicz

12/31/2007 5:45:00 AM

On Dec 30, 2007, at 7:52 PM, Abraham Tio wrote:

> need a class(we'll call it a 'simulator' since that's what i'm
> attempting to write) to run a loop.
> need that loop to stop when asked to, such as when the user that
> started
> it clicks a button to stop it.
>
> i write java that does this sort of thing all the time.
> HOWEVER, when i try it in ruby, only bad things happen.
>
> check this out:
>
> ***start r.rb***
> class Simulator
> attr_accessor :running
> attr_accessor :sim_thread
> def start
> running = true

self.running = true

>
> puts "starting simulator..."
> sim_thread= Thread.new(){
> puts "sim thread started"
> while(running)
> 300000.times do |x|
> x+=1
> end
> puts 'did a buncha stuff a simulator might do'
> Thread.pass
> end
> puts "sim thread stopped"
> }
> sim_thread.join
> sim_thread
> end
> def stop
> puts "stopping simulator..."
> running = false

self.running = false
>
> end
> end
> Thread.abort_on_exception = true
> simulator = Simulator.new
> thread = simulator.start
> puts "started simulator, now we stop it.."
> simulator.stop
> ***end r.rb***

You have an attr_accessor :running but you were assigning to a
running local variable. You need to either use @running = true or
self.running = true> When ruby sees 'running = true' it decides that
running is a local variable, so using running = does not set the
@running ivar via the attr_acessor but self.running = true does.

Cheers-
- Ezra Zygmuntowicz
-- Founder & Software Architect
-- ezra@engineyard.com
-- EngineYard.com

Tiziano Merzi

12/31/2007 8:53:00 AM

Abraham Tio wrote:
> need a class(we'll call it a 'simulator' since that's what i'm
> attempting to write) to run a loop.
> need that loop to stop when asked to, such as when the user that started
> it clicks a button to stop it.
>
> i write java that does this sort of thing all the time.
> HOWEVER, when i try it in ruby, only bad things happen.
>
> check this out:
>

here a woking code

class Simulator
attr_accessor :running
attr_accessor :sim_thread
def start
@running = true; #instance var
puts "starting simulator..."
@sim_thread= Thread.new(){ #instance var
puts "sim thread started"
while(@running)
300000.times do |x|
x+=1
end
puts 'did a buncha stuff a simulator might do'
Thread.pass
end
puts "sim thread stopped"
}
# @sim_thread.join no join
@sim_thread
end
def stop
puts "stopping simulator..."
@running = false
end
end
Thread.abort_on_exception = true
simulator = Simulator.new
thread = simulator.start
puts "started simulator, now we stop it.."
simulator.stop
# wait simulator end
simulator.sim_thread.join

Enjoy!
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