Select in Julia

Julia’s Channels and tasks allow you to wait on multiple operations simultaneously. Combining tasks and channels with select is a powerful feature of Julia.

using Dates

function main()
    # For our example we'll select across two channels.
    c1 = Channel{String}(1)
    c2 = Channel{String}(1)

    # Each channel will receive a value after some amount
    # of time, to simulate e.g. blocking RPC operations
    # executing in concurrent tasks.
    @async begin
        sleep(1)
        put!(c1, "one")
    end
    @async begin
        sleep(2)
        put!(c2, "two")
    end

    # We'll use `@select` to await both of these values
    # simultaneously, printing each one as it arrives.
    for i in 1:2
        @select begin
            msg1 = take!(c1) => println("received ", msg1)
            msg2 = take!(c2) => println("received ", msg2)
        end
    end
end

main()

We receive the values "one" and then "two" as expected.

$ julia select.jl
received one
received two

Note that the total execution time is only ~2 seconds since both the 1 and 2 second sleeps execute concurrently.

real    0m2.245s

In this Julia version:

1. We use Channel{String}(1) to create buffered channels that can hold one string each.
2. Instead of goroutines, we use Julia’s @async macro to create tasks that run concurrently.
3. The select statement in Go is replaced by Julia’s @select macro, which has a similar functionality.
4. We use put! to send values to channels and take! to receive from them.
5. The fmt.Println function is replaced with Julia’s println.

The overall structure and behavior of the program remain the same, demonstrating how to wait on multiple channel operations simultaneously in Julia.