Possibly blocking call in non-blocking context

Reports thread-blocking method calls in code fragments where threads should not be blocked.

Example (Project Reactor):

Flux.just("1").flatMap(f -> {
    Flux<String> just = loadUsersFromDatabase();
    just.toIterable(); // Error: blocking operator call in non-blocking scope
    return just;
  }
);

Consider running blocking code with a proper scheduler, for example Schedulers.boundedElastic(), or try to find an alternative non-blocking API.

Example (Kotlin Coroutines):

suspend fun exampleFun() {
    Thread.sleep(100); // Error: blocking method call inside suspend function
}

Consider running blocking code with a special dispatcher, for example Dispatchers.IO, or try to find an alternative non-blocking API.

Locating this inspection

By ID

Can be used to locate inspection in e.g. Qodana configuration files, where you can quickly enable or disable it, or adjust its settings.

BlockingMethodInNonBlockingContext

Via Settings dialog

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

Settings or Preferences | Editor | Inspections | JVM languages

Configure the inspection:

In the Blocking Annotations list, specify annotations that mark thread-blocking methods.
In the Non-Blocking Annotations list, specify annotations that mark non-blocking methods.

Specified annotations can be used as External Annotations

Inspection options

Here you can find the description of settings available for the Possibly blocking call in non-blocking context inspection, and the reference of their default values.

Consider unknown contexts blocking: Default: Selected
Consider Kotlin suspend context non-blocking: Default: Selected
Blocking annotations: [org.jetbrains.annotations.Blocking, io.micronaut.core.annotation.Blocking, io.smallrye.common.annotation.Blocking]
Non-blocking annotations: [org.jetbrains.annotations.NonBlocking, io.micronaut.core.annotation.NonBlocking, io.smallrye.common.annotation.NonBlocking]

Availability

By default bundled with: IntelliJ IDEA 2024.1, Qodana for JVM 2024.1,
Can be installed with plugin: Java, 241.18072

Last modified: 18 June 2024