Understanding Kotlin Coroutines: Suspend and RunBlocking Functions

Suspend Functions: The Building Blocks of Coroutines

A suspend function is a special type of function that can be paused and resumed at specific points, allowing other coroutines to run in between. This pausing and resuming mechanism enables efficient concurrency and asynchronous programming. Suspend functions are marked with the suspend keyword and can only be called from within another suspend function or a coroutine.

CoroutineScope: The Context for Suspend Functions

To execute suspend functions, you need a coroutine scope, which is an object that provides a context for coroutines to run in. A coroutine scope can be created using the coroutineScope function, which returns a scope that can be used to launch coroutines. The coroutineScope function is itself a suspend function, which means it can only be called from within another suspend function or a coroutine.

RunBlocking Function: A Bridge to the Non-Coroutine World

The runBlocking function is a coroutine builder that creates a coroutine scope and blocks the current thread until the coroutine completes. This function is used to bridge the non-coroutine world of regular functions with the coroutine world. Unlike suspend functions, runBlocking is not a suspend function itself, but it creates a coroutine scope that can be used to launch coroutines.

How Suspend and RunBlocking Functions Relate

To understand how suspend and runBlocking functions relate, let’s consider an example:

fun main() {
    runBlocking {
        println("Follow")
        suspendingWork()
        println("the")
    }
    println("execution")
}

suspend fun suspendingWork() {
    delay(1000)
    println("delayed work")
}

In this example, the main function creates a coroutine scope using runBlocking, which blocks the current thread until the coroutine completes. Within the coroutine scope, the suspendingWork function is called, which is a suspend function that delays its execution by 1 second. The runBlocking scope waits for the suspendingWork function to complete before continuing execution.

More Examples and Use Cases

Here are a few more examples to illustrate the relationship between suspend and runBlocking functions:

• Example 1: Launching multiple coroutines within a runBlocking scope

  fun main() {
      runBlocking {
          launch { suspendingWork() }
          launch { suspendingWork() }
          println("Hello")
      }
  }

• Example 2: Using runBlocking to create a coroutine scope that can be used to launch coroutines

  fun main() {
      val scope = runBlocking {
          coroutineScope {
              launch { suspendingWork() }
              launch { suspendingWork() }
          }
      }
  }

• Example 3: Creating a coroutine scope within a suspend function

  suspend fun suspendingWork() {
      coroutineScope {
          launch { println("nested coroutine") }
      }
  }

By using these functions correctly, you can write efficient and readable code that takes advantage of the coroutine paradigm.