Threads output/execution question


#1

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


#2

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


#3

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