How to run computations for n seconds in Julia? - julia

Question

I'd like to run heavy computations in Julia for a fixed duration, for example 10 seconds. I tried this:
timer = Timer(10.0)
while isopen(timer)
computation()
end
But this does not work, since the computations never let Julia's task scheduler take control. So I added yield() in the loop:
timer = Timer(10.0)
while isopen(timer)
yield()
computation()
end
But now there is significant overhead from calling yield(), especially when one call to computation() is short. I guess I could call yield() and isopen() only every 1000 iterations or so, but I would prefer a solution where I would not have to tweak the number of iterations every time I change the computations. Any ideas?

Answer 1

This pattern below uses threads and on my laptop has a latency of around 35ms for each 1,000,000 calls which is more than acceptable for any job.
Tested on Julia 1.5 release candidate:
function should_stop(timeout=10)
handle = Threads.Atomic{Bool}(false)
mytask = Threads.#spawn begin
sleep(timeout)
Threads.atomic_or!(handle, true)
end
handle
end
function do_some_job_with_timeout()
handle = should_stop(5)
res = BigInt() # save results to some object
mytask = Threads.#spawn begin
for i in 1:10_000_000
#TODO some complex computations here
res += 1 # mutate the result object
handle.value && break
end
end
wait(mytask) # wait for the job to complete
res
end
You can also used Distributed instead. The code below seems to have a much better latency - only about 1ms for each 1,000,000 timeout checks.
using Distributed
using SharedArrays
addprocs(1)
function get_termination_handle(timeout=5,workerid::Int=workers()[end])::SharedArray{Bool}
handle = SharedArray{Bool}([false])
proc = #spawnat workerid begin
sleep(timeout)
handle[1]=true
end
handle
end
function fun_within_timeout()
res = 0
h = get_termination_handle(0.1)
for i = 1:100_000_000
res += i % 2 == 0 ? 1 : 0
h[1] && break
end
res
end