83 lines
3.7 KiB
Markdown
83 lines
3.7 KiB
Markdown
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[//]: # (title: Debug coroutines using IntelliJ IDEA – tutorial)
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This tutorial demonstrates how to create Kotlin coroutines and debug them using IntelliJ IDEA.
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The tutorial assumes you have prior knowledge of the [coroutines](coroutines-guide.md) concept.
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> Debugging works for `kotlinx-coroutines-core` version 1.3.8 or later.
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>
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{type="note"}
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## Create coroutines
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1. Open a Kotlin project in IntelliJ IDEA. If you don't have a project, [create one](jvm-get-started.md#create-an-application).
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2. Open the `main.kt` file in `src/main/kotlin`.
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The `src` directory contains Kotlin source files and resources. The `main.kt` file contains sample code that will print `Hello World!`.
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3. Change code in the `main()` function:
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* Use the [`runBlocking()`](https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/run-blocking.html) block to wrap a coroutine.
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* Use the [`async()`](https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/async.html) function to create coroutines that compute deferred values `a` and `b`.
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* Use the [`await()`](https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-deferred/await.html) function to await the computation result.
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* Use the [`println()`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.io/println.html) function to print computing status and the result of multiplication to the output.
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```kotlin
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import kotlinx.coroutines.*
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fun main() = runBlocking<Unit> {
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val a = async {
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println("I'm computing part of the answer")
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6
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}
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val b = async {
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println("I'm computing another part of the answer")
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7
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}
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println("The answer is ${a.await() * b.await()}")
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}
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```
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4. Build the code by clicking **Build Project**.
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## Debug coroutines
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1. Set breakpoints at the lines with the `println()` function call:
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2. Run the code in debug mode by clicking **Debug** next to the run configuration at the top of the screen.
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The **Debug** tool window appears:
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* The **Frames** tab contains the call stack.
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* The **Variables** tab contains variables in the current context.
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* The **Coroutines** tab contains information on running or suspended coroutines. It shows that there are three coroutines.
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The first one has the **RUNNING** status, and the other two have the **CREATED** status.
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3. Resume the debugger session by clicking **Resume Program** in the **Debug** tool window:
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Now the **Coroutines** tab shows the following:
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* The first coroutine has the **SUSPENDED** status – it is waiting for the values so it can multiply them.
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* The second coroutine is calculating the `a` value – it has the **RUNNING** status.
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* The third coroutine has the **CREATED** status and isn’t calculating the value of `b`.
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4. Resume the debugger session by clicking **Resume Program** in the **Debug** tool window:
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Now the **Coroutines** tab shows the following:
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* The first coroutine has the **SUSPENDED** status – it is waiting for the values so it can multiply them.
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* The second coroutine has computed its value and disappeared.
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* The third coroutine is calculating the value of `b` – it has the **RUNNING** status.
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Using IntelliJ IDEA debugger, you can dig deeper into each coroutine to debug your code.
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