julia - 如何等待第一个任务完成

Question

如果有一组并发任务被调度，如何等待第一个任务完成？

是否存在类似wait([t1, t2], return_when=:FIRST_COMPLETED) 的东西？

function task1()
    rt = rand()
    @info "task1 time: $rt"
    sleep(rt)
    @info "task 1 done"
end

function task2()
    rt = rand()
    @info "task2 time: $rt"
    sleep(rt)
    @info "task 2 done"
end

t1 = @async task1()
t2 = @async task2()

# wait for just the first completed task
# ??? 

Answer 1

我认为这样的事情会起作用:

julia> function waitfirst(ts)
           c = Channel{Int}()
           for (i, t) in enumerate(ts)
               @async begin
                   wait(t)
                   put!(c, i)
               end
           end
           r = take!(c)
           @info "Task $r won"
       end
waitfirst (generic function with 1 method)

julia> waitfirst([@async(task1()), @async(task2())])
[ Info: task1 time: 0.6723665203367726
[ Info: task2 time: 0.4815093245244271
[ Info: task 2 done
[ Info: Task 2 won

julia> [ Info: task 1 done
julia> 

julia> waitfirst([@async(task1()), @async(task2())])
[ Info: task1 time: 0.3452659680724035
[ Info: task2 time: 0.8576370382519976
[ Info: task 1 done
[ Info: Task 1 won

julia> [ Info: task 2 done
julia> 

不过，您必须确保首先安排输入，否则会发生死锁。