What Are coroutines In Julia?

A coroutine can be defined as a generalized subroutine in Julia, which is a set of instructions stored in memory and invoked during execution.

As the Julia language has been created to provide faster computation, coroutines allow us to create multiple subroutines using the @task macro. These tasks are then invoked by scheduling them through the schedule() function. Unless the tasks are invoked, they stay in a runnable but dormant state.

Note: Coroutines are not a type of parallel processing. They simply allow the creation of more than one subroutines simultaneously.

Code Example

using Distributed
using Base
# Pell numbers
function pell_generator(n)
    a, b = (0, 1)
    for i = 1:n
        a, b = (b, 2 * b + a)
    end
    return a, b
end
gen1 = @task pell_generator(5)
# Generator state
println("State of Pell generator: ", gen1.state)
println("Has Pell generator started: ", istaskstarted(gen1))
# Start Pell generator
println("\n-------------------Start Pell generator-------------------")
schedule(gen1)
yield() 
println("Has Pell generator started: ", istaskstarted(gen1))
println("Pell sequence: ", gen1.result)
println("State of Pell generator: ", gen1.state)

In this code example:

Lines 4–11: A function pell_generator(n) is defined, which returns the Pell numbers after n iterations.
Line 13: The function is wrapped in a task. This creates a subroutine.
Line 16: The current state of the generator is printed.
Line 17: It checks whether the task has started or not.
Line 21–22: The task is scheduled and executed.
Line 23: It checks if the task has started. The task has started now.
Line 25: The result of the generator function is displayed.
Line 26: The current state of the generator is printed.

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