# Producer/Consumer Tasks Do Not End Properly
**URL:** https://discourse.julialang.org/t/producer-consumer-tasks-do-not-end-properly/16645
**Category:** Julia at Scale
**Created:** [October 22, 2018, 6:38pm UTC](https://discourse.julialang.org/t/producer-consumer-tasks-do-not-end-properly/16645 "2018-10-22T18:38:14Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@zekeriya.sari](https://discourse.julialang.org/u/zekeriya.sari)
#### Post date: [October 22, 2018, 6:38pm UTC](https://discourse.julialang.org/t/producer-consumer-tasks-do-not-end-properly/16645/1 "2018-10-22T18:38:14Z")
I want to construct an unbuffered channel and bind a producer task feeding the channel for some certain amount of data and a consumer task consuming the produced data in in infinite loop until a poission pill is taken. The script for this problem is given below.
```julia
function producer(ch)
for i = 1 : 10
put!(ch, i)
end
end
function consumer(ch)
while true
val = take!(ch)
val === NaN && break
println("Took ", val)
end
end
channel = Channel(0)
producer_task = @task producer(channel)
schedule(producer_task)
yield()
consumer_task = @task consumer(channel)
schedule(consumer_task)
yield()
put!(channel, NaN) # Poission pill.
println(consumer_task)
```
The problem is that when I run the whole script at once using ctrl+shift+enter in Juno, I got the following console output,
```julia
Took 1
Task (done) @0x00007f4039ad4a90
```
which implies that the tasks do not work properly. However, when I execute the same script line by line using ctrl+enter in Juno, I get the following console output,
```julia
Took 1
Took 2
Took 3
Took 4
Took 5
Took 6
Took 7
Took 8
Took 9
Took 10
Task (done) @0x00007f403a734550
```
which implies that the tasks work properly. But if I insert a short sleep time before the poissson pill as shown below
```julia
# see the full script above
yield()
sleep(eps())
put!(channel, NaN) # Poission pill.
# see the full script above
```
the whole script works properly using ctrl+shift+enter.
I can undertand that certain amount of time is required before poission pilling the consumer task but what is the reason of this required time. (I assume that this time is required for the scheduler to do the things right.). And, is there any other possible way to terminate the consumer task harmlessly( i.e. not abruptly closing the channel)?
By the way I realized that minimum sleep time is 1 milisecond. So a sleep of eps() time is not possible.
---
### Author:  [@tim.holy](https://discourse.julialang.org/u/tim.holy)
#### Post date: [October 23, 2018, 2:09am UTC](https://discourse.julialang.org/t/producer-consumer-tasks-do-not-end-properly/16645/2 "2018-10-23T02:09:25Z")
It’s an interesting but slightly confusing case because `println` causes a `yield`, so your consumer is yielding partway through execution. A slightly easier-to-understand example might be
```julia
function producer(ch)
for i = 1 : 10
put!(ch, i)
end
end
const output = []
const broken = Ref(false)
function consumer(ch)
while true
val = take!(ch)
val === NaN && (broken[] = true; break)
push!(output, val)
end
end
```
in one file (so you can load your function definitions once and don’t have to wonder about compilation time, etc) and
```julia
empty!(output)
broken[] = false
channel = Channel(0)
producer_task = @task producer(channel)
schedule(producer_task)
yield()
consumer_task = @task consumer(channel)
schedule(consumer_task)
for i = 1:6
yield()
end
put!(channel, NaN) # Poission pill.
println(output)
println(consumer_task)
println(output)
println(broken)
```
You’ll see that however many loops are taken, that’s the number of elements in `output`.
---
### Author:  [@zekeriya.sari](https://discourse.julialang.org/u/zekeriya.sari)
#### Post date: [October 23, 2018, 7:15pm UTC](https://discourse.julialang.org/t/producer-consumer-tasks-do-not-end-properly/16645/3 "2018-10-23T19:15:28Z")
@tim.holy thank you for your informative reply. That solved the problem.