task_async.md

1.

@async will return a "Task" type. Use fetch() to get value.

t = @async 1+1

#>>Task (done) @0x00007f64619e8550

fetch(t)

#>>2

2.

Fucntion to calculate pi:

function work(N)
    series = 1.0
    for i in 1:N
        series += (isodd(i) ? -1 : 1) / (i*2+1)
    end
    return 4*series
end

#precompile
work(100)

@time work(100_000_000)

#>>0.178186 seconds (5 allocations: 176 bytes)

3. do each task one-by-one.

@time @sync for i in 1:10
    @async work(100_000_000)
end

#>>1.844235 seconds (77.87 k allocations: 3.771 MiB)

Time is the same as for-loop

@time for i in 1:10
    t = @async work(100_000_000)
    fetch(t)
end

#>>1.714652 seconds (24.96 k allocations: 1.349 MiB) or

@time  for i in 1:10
     work(100_000_000)
end

#>>1.721287 seconds

4.

• @async creates and starts running a task
• @sync waits for them to all complete

@time for i in 1:10
    t = @async work(100_000_000)
end

#>> 0s

But this code makes no sense because we always want to know the answer.

5. Sleep() is special because sleep is nicely cooperating with tasks. Avoid testing with sleep().

@time @sync for i in 1:10
    @async sleep(1)
end

#>>1.007097 seconds (2.02 k allocations: 133.505 KiB)