# Problem with @async and remotecall\_fetch()

**URL:** <https://discourse.julialang.org/t/problem-with-async-and-remotecall-fetch/65022>\
**Category:** General Usage\
**Tags:** question, distributed\
**Created:** [July 21, 2021, 7:08am UTC](https://discourse.julialang.org/t/problem-with-async-and-remotecall-fetch/65022 "2021-07-21T07:08:11Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![WeiMXi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/weimxi/32/19971_2.png) [@WeiMXi](https://discourse.julialang.org/u/WeiMXi)\
**Post date:** [July 21, 2021, 7:08am UTC](https://discourse.julialang.org/t/problem-with-async-and-remotecall-fetch/65022/1 "2021-07-21T07:08:12Z")

</div>

I have the following code, my purpose is assigning the tasks to the different workers, and print the progress.

```julia
# bug.jl

# a simple calculation task
function cal_one_task(size)
    a = rand(size)
    sum(a)
end

# manage tasks on different workers and print progress
function auto_manger(task)
    # total number of the tasks
    num_of_task = length(task)
    # Get the number of remote processes
    numof_workers = length(workers())
    result = []
    workersFuture = [Future(1) for i in 1:numof_workers]
    # record the position of the completed task ID in the workers() list
    c = Channel{Int64}(numof_workers)

    progress = 0.0

    # Start numof_workers number of processes at the same time
    for i in 1:numof_workers
        @async begin; put!(workersFuture[i], remotecall_fetch(cal_one_task, workers()[i], task[i])); put!(c, i); end
    end

    # i is the index where the next data is stored in the result
    # (i-1) is the number of recorded data
    # and (i-1 + numof_workers) is the number of processes that have been started
    # when the number of started processes is less than num_of_task, the result of the process that has completed the task is continuously recorded, and the calculation task is started after the process of completing the task
    # after starting num_of_task number of processes, wait for the remaining running process (the last one) and return the result
    i = 1
    test_num = 0
    while true
            
        # index of the process that completed the task
        j = take!(c)
        # get the result
        push!(result, fetch(workersFuture[j]))
        workersFuture[j] = Future(1)
        println("up $i #")

        if i < num_of_task
            @async begin; put!(workersFuture[j], remotecall_fetch(cal_one_task, workers()[j], task[i + numof_workers])); put!(c, j); end;
            # test_num = test_num + 1
            # println("test_num $test_num")
            ## print progress
            if (i - 1)/num_of_task > 0.001 + progress
                progress = i/num_of_task
                print("\r")
                print(round(progress*100, digits = 1))
                print("%")
            end
            ## print progress
        else
            break
        end
        i = i + 1
    end

    close(c)
    print(" all done @")
    println(now())
    result
end

```

Then just run the following commands in REPL, we can start compute

```julia
using Distributed
using Dates
@everywhere include("./bug.jl")
my_tasks = [10^8 for i in 1:10];
auto_manger(my_tasks)

```

The incredible thing is that the above program is always stuck on the last task, always in the waiting state for `j = take! (c)`  
What is even more bizarre is that when I remove the `#` below, that is, after `@async`, print the variable `test_num`

```julia
            # test_num = test_num + 1
            # println("test_num $test_num")

```

Then the program will end normally!

 ![image](https://global.discourse-cdn.com/julialang/original/3X/a/d/adc073a24e86201aedf4ed48e845aba4eb4c6c28.png)

---

<div class="post-metadata">

**Author:** ![WeiMXi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/weimxi/32/19971_2.png) [@WeiMXi](https://discourse.julialang.org/u/WeiMXi)\
**Post date:** [July 21, 2021, 11:46am UTC](https://discourse.julialang.org/t/problem-with-async-and-remotecall-fetch/65022/2 "2021-07-21T11:46:57Z")

</div>

I posted the same topic in the chinese julia furum. It seems that I found the solution.

> **[关于并行计算的Bug?](https://discourse.juliacn.com/t/topic/5391/6?u=weiming)**
>
> 哦，解决的方法就是在本地计算i + numof\_workers就好 比如说 the\_task = task\[i + numof\_workers\] the\_id = workers()\[j\] the\_j = j @async begin; put!(workersFuture\[the\_j\], remotecall\_fetch(cal\_one\_task, the\_id, the\_task)); put!(c, the\_j); end 目前算是可以正常运行， ...