How to cancel other futures? - concurrent-ruby

Question

I am creating multiple futures and I am expecting only one to achieve the desired goal.
How can I cancel all other futures from within a future?
This is how I create futures:
jobs = days_to_scan.map{|day|
Concurrent::Future.execute do
sleep_time = day.to_f / days_to_scan.count.to_f * seconds_to_complete.to_f
sleep (sleep_time)
if GoogleAPI.new.api_call(#adwords, ad_seeder, visitor, day)
# How to cancel other futures here?
end
end
}

Answer 1

I might be late to the party but I'm gonna reply anyway as other people might stumble upon this question.
So what you want is to probably force-shutdown the thread pool as soon as one Future finishes:
class DailyJobs
def call
thread_pool = ::Concurrent::CachedThreadPool.new
jobs = days_to_scan.map{ |day|
Concurrent::Future.execute(executor: thread_pool) do
sleep_time = day.to_f / days_to_scan.count.to_f * seconds_to_complete.to_f
sleep (sleep_time)
if GoogleAPI.new.api_call(#adwords, ad_seeder, visitor, day)
# How to cancel other futures here?
thread_pool.kill
end
end
}
end
end
the thing is: killing a thread pool is not really recommended and might have unpredictable results
a better approach is to track when a Future is done and ignore other Futures:
class DailyJobs
def call
status = ::Concurrent::AtomicBoolean.new(false)
days_to_scan.map{ |day|
Concurrent::Future.execute do
return if status.true? # Early return so Future does nothing
sleep_time = day.to_f / days_to_scan.count.to_f * seconds_to_complete.to_f
sleep (sleep_time)
if GoogleAPI.new.api_call(#adwords, ad_seeder, visitor, day)
# Do your thing
status.value = true # This will let you know that at least one Future completed
end
end
}
end
end
It is worth noting that if this is a Rails application, you probably want to wrap your Future on Rails executor to avoid autoloading and deadlock issues. I wrote about it here

Answer 2

Okey, I could implement it as:
#wait until one job has achieved the goal
while jobs.select{|job| job.value == 'L' }.count == 0 && jobs.select{|job| [:rejected, :fulfilled].include?(job.state) }.count != jobs.count
sleep(0.1)
end
#cancel other jobs
jobs.each{|job| job.cancel unless (job.state == :fulfilled && job.value == success_value) }
}