# Threads output/execution question

**URL:** <https://www.ruby-forum.com/t/threads-output-execution-question/103583>\
**Category:** Ruby\
**Created:** [May 8, 2007, 4:15am UTC](https://www.ruby-forum.com/t/threads-output-execution-question/103583 "2007-05-08T04:15:36Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [May 8, 2007, 4:15am UTC](https://www.ruby-forum.com/t/threads-output-execution-question/103583/1 "2007-05-08T04:15:36Z")

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Hi,

I have a ruby multi-threaded application and I don’t understand its  
behaviour. I hate just dumping code in a post and asking questions,  
but I cannot explain the problem otherwise. In the code below, I have  
a loop which requests user input to either start/stop a job. The  
execution of the job will happen in a separate thread, because the job  
can terminate unexpectedly. What I don’t understand in the code, is  
why doesn’t the application just print “Job.start” and  
“'DummyThreads.start” after 5 seconds in the same standard output  
screen (as where it is receiving input). It is not even about the  
screen (I tried putting STDOUT.flush after every puts statement), the  
code is not even executed until I subsequently call DummyThreads  
again.

So, what I get is:  
Enter option: 1  
[…more than 5 seconds passed…]  
Enter option: 1  
[…immediately…]  
Job.start  
DummyThreads.start  
Enter option:  
[…]

What I expected is:  
Enter option: 1  
Enter option:  
[…after 5 seconds…]  
Job.start  
DummyThreads.start  
[…]

Thanks,  
Tiberiu

PS. here is my code

class Job  
def run  
sleep 5  
puts ‘Job.start’  
end  
def kill  
sleep 5  
puts ‘Job.stop’  
end  
end

class DummyThreads  
def initialize  
@job = Job.new  
end  
def start  
t = Thread.new { @job.run; puts ‘DummyThreads.start’ }  
t.join  
end  
def stop  
t = Thread.new { @job.kill; puts ‘DummyThreads.stop’ }  
t.join  
end  
end

# create DummyThreads

dummythreads = DummyThreads.new

# get user input

puts 'Enter option: ’  
STDOUT.flush  
while option = gets  
case option.to\_i  
when 1: t = Thread.new { dummythreads.start }  
when 2: t = Thread.new { dummythreads.stop }  
when 0: break  
end  
puts 'Enter option: ’  
STDOUT.flush  
end

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [May 8, 2007, 11:36am UTC](https://www.ruby-forum.com/t/threads-output-execution-question/103583/2 "2007-05-08T11:36:52Z")

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On 08.05.2007 04:14, removed\_email\_address@domain.invalid wrote:

> screen (as where it is receiving input). It is not even about the  
> DummyThreads.start
> 
> def kill  
> t = Thread.new { @job.run; puts ‘DummyThreads.start’ }
> 
> STDOUT.flush  
> end

IMHO you have too many threads in there. Try this for an alternative:

robert

class Job  
class JobTermination \< Exception; end

def run  
@thread = Thread.current  
begin  
puts ‘Job.start’  
work  
puts ‘Job.finish’  
rescue JobTermination  
puts ‘Job.killed’  
ensure  
@thread = nil  
end  
end  
def kill  
puts ‘Job.stop’  
@thread.raise JobTermination if @thread  
end

private  
def work  
sleep 5  
end  
end

class DummyThreads  
def initialize  
@job = Job.new  
end  
def start  
puts ‘DummyThreads.start’  
Thread.new { @job.run }  
end  
def stop  
@job.kill  
puts ‘DummyThreads.stop’  
end  
end

# create DummyThreads

dummythreads = DummyThreads.new

# get user input

puts 'Enter option: ’  
STDOUT.flush  
while option = gets  
case option.to\_i  
when 1: dummythreads.start  
when 2: dummythreads.stop  
when 0: break  
end  
puts 'Enter option: ’  
STDOUT.flush  
end

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [May 8, 2007, 9:45pm UTC](https://www.ruby-forum.com/t/threads-output-execution-question/103583/3 "2007-05-08T21:45:44Z")

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Hi Robert,

Thanks so much for your answer. Actually even with your code I had the  
same problem. If I would wait for more than 5 seconds, the worker  
thread would not print “Job.finish” (Job.finish would be printed after  
my subsequent input). I realized in both cases that the line “while  
option = gets” was blocking the thread from outputing.

Tiberiu