Parallel Map in Kotlin
Ever wonder how to run
map in parallel using coroutines? This is how you do it.
Confused? Let’s unpack it.
First we have the function signature which is pretty similar to the actual
map extension function signature on
Iterable. The only thing we added was the
suspend keyword on the parameter, which let’s us use
suspend functions in
f (as we’re going to see in a moment).
Then we have the
runBlocking which let’s us bridge the blocking code with the coroutine world. As the name suggests this will block the current thread until everything inside the block finishes executing. Which is exactly what we want.
Finally we have the actual execution which is divided in 2 steps. The first step launches a new coroutine for each function application using
async. This effectively wraps the type of each element with
Deferred. In the second step we wait for all function applications to complete and unwrap the result with
How to use it
Easy! Just like you use
(Psst! I’m using Kotlin Playground so you can actually run this code!)
Prove that it’s running in parallel
Ok so let’s resort to the good old
delay to prove that this is actually running in parallel. We are going to add a delay of 1 second on each multiplication and measure the time it takes to run.
Running over 100 elements the result should be: close to 1,000 milliseconds if it’s running in parallel and close to 100,000 milliseconds if it’s running sequentially.
Since I’m not explicitly passing any
DefaultDispatcherwill be used. ↩