What is the difference between launch/join and async/await in Kotlin coroutines

In Kotlin coroutines, launch/join and async/await are two commonly used mechanisms for handling different concurrent programming scenarios.

1. launch/join

Definition and Usage:

• launch is a coroutine builder that starts a new coroutine within the current coroutine scope (CoroutineScope), but it does not block the current thread and does not directly return results.
• Once the coroutine is launched, launch returns a Job object, which allows you to call the join() method to wait for the coroutine to complete.

Scenario Example: Suppose you need to perform a time-consuming logging operation in the background, but you do not need the result; you only need to ensure it completes. In this case, you can use launch to start this time-consuming operation and then wait for it to complete when needed using join.

kotlin
val job = launch {
    // Perform time-consuming logging operation
}
job.join() // Wait for the coroutine to complete when needed

2. async/await

Definition and Usage:

• async is also a coroutine builder used to start a new coroutine within the coroutine scope. Unlike launch, async returns a Deferred object, which is a non-blocking future-like value representing that a result will be provided later.
• You can retrieve the result of the asynchronous operation when needed by calling the await() method on the Deferred object. This call will suspend the current coroutine until the asynchronous operation completes and returns the result.

Scenario Example: For example, if you need to fetch data from the network and process it, and the data fetching is asynchronous requiring the result to continue execution, you can use async to initiate the network request and retrieve the result using await.

kotlin
val deferred = async {
    // Initiate network request and return result
    fetchDataFromNetwork()
}
val data = deferred.await() // Wait for the result to continue processing
processData(data)

Summary

In summary:

• launch/join is used for scenarios where you do not need direct results and only require parallel task execution.
• async/await is used for scenarios where you need to obtain the result of an asynchronous operation and continue with further processing.

Both are effective tools for handling asynchronous tasks in coroutines, and the choice depends on whether you need to obtain results from the coroutine.