Callbacks on parts of sharedarrays

When working with shared arrays in Julia, it can be useful to have callbacks that are triggered when specific parts of the array are modified. In this article, we will explore three different ways to implement callbacks on parts of shared arrays in Julia.

Option 1: Using Observables.jl

One way to implement callbacks on parts of shared arrays is by using the Observables.jl package. This package provides a simple and efficient way to create observables, which are objects that can be subscribed to and trigger callbacks when their value changes.

using Observables

function create_shared_array_with_callbacks()
    shared_array = SharedArray{Int}(10)
    observables = Observables.Observable{Int}[]
    
    for i in 1:length(shared_array)
        observable = Observables.Observable(shared_array[i])
        push!(observables, observable)
        
        Observables.on(observable) do value
            println("Element $i of the shared array changed to $value")
        end
    end
    
    return shared_array, observables
end

shared_array, observables = create_shared_array_with_callbacks()

shared_array[5] = 42

In this code snippet, we create a shared array of integers with a length of 10. We also create an array of observables, where each observable corresponds to an element in the shared array. We then use the `Observables.on` function to define a callback that prints a message whenever an element in the shared array changes.

Option 2: Using Reactive.jl

Another option is to use the Reactive.jl package, which provides a reactive programming framework for Julia. Reactive.jl allows you to define reactive expressions that automatically update when their dependencies change.

using Reactive

function create_shared_array_with_callbacks()
    shared_array = SharedArray{Int}(10)
    callbacks = Callback[]
    
    for i in 1:length(shared_array)
        callback = Callback(() -> println("Element $i of the shared array changed to $(shared_array[i])"))
        push!(callbacks, callback)
    end
    
    return shared_array, callbacks
end

shared_array, callbacks = create_shared_array_with_callbacks()

shared_array[5] = 42

In this code snippet, we create a shared array of integers with a length of 10. We also create an array of callbacks, where each callback corresponds to an element in the shared array. The callbacks are defined using a lambda function that prints a message whenever an element in the shared array changes.

Option 3: Using Julia’s built-in event system

Julia has a built-in event system that can be used to implement callbacks on parts of shared arrays. This option is more low-level compared to the previous two options, but it provides more flexibility and control over the callback mechanism.

function create_shared_array_with_callbacks()
    shared_array = SharedArray{Int}(10)
    callbacks = Dict{Int, Function}()
    
    for i in 1:length(shared_array)
        callbacks[i] = () -> println("Element $i of the shared array changed to $(shared_array[i])")
    end
    
    return shared_array, callbacks
end

shared_array, callbacks = create_shared_array_with_callbacks()

shared_array[5] = 42

In this code snippet, we create a shared array of integers with a length of 10. We also create a dictionary of callbacks, where each callback corresponds to an element in the shared array. The callbacks are defined as anonymous functions that print a message whenever an element in the shared array changes.

After exploring these three options, it is clear that using Observables.jl is the best choice for implementing callbacks on parts of shared arrays in Julia. Observables.jl provides a simple and efficient way to create observables and define callbacks, making it easy to track changes in shared arrays. Additionally, Observables.jl has a well-documented API and a large community, which makes it a reliable and well-supported choice for this task.