Relation of coroutines, threads, and Tasks

General Usage
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If we are just talking solely about Julia and it’s standard library, the only interface you have to threads are Tasks.

Notice that when you use Thread.@spawn you get a Task:

julia> Threads.@spawn sleep(5)
Task (runnable) @0x00007f3fee5beca0

If you look under the hood, you will see that all Theads.@spawn does is create a Task and sets the sticky property to false.

julia> @macroexpand Threads.@spawn sleep(5)
quote
    #= threadingconstructs.jl:181 =#
    let
        #= threadingconstructs.jl:182 =#
        local var"#3#task" = Base.Threads.Task((()->begin
                            #= threadingconstructs.jl:178 =#
                            sleep(5)
                        end))
        #= threadingconstructs.jl:183 =#
        (var"#3#task").sticky = false
        #= threadingconstructs.jl:184 =#
        if $(Expr(:islocal, Symbol("##sync#41")))
            #= threadingconstructs.jl:185 =#
            Base.Threads.put!(var"##sync#41", var"#3#task")
        end
        #= threadingconstructs.jl:187 =#
        Base.Threads.schedule(var"#3#task")
        #= threadingconstructs.jl:188 =#
        var"#3#task"
    end
end

The interface to threads in Julia is Task-based. Sometimes the Task may run on a different thread if you used Threads.@spawn.

A Channel is used for communicating between Tasks whether be on the same thread or not. If you look in the documentation of Channel you should see a spawn keyword:

If spawn = true, the Task created for func may be scheduled on another thread in parallel, equivalent to creating a task via Threads.@spawn.

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