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

Suppressing Inspection

You can suppress this inspection by placing the following comment marker before the code fragment where you no longer want messages from this inspection to appear:

//noinspection BlockingMethodInNonBlockingContext

More detailed instructions as well as other ways and options that you have can be found in the product documentation:

IntelliJ IDEA 2025.2

Inspection Details
By default bundled with:	IntelliJ IDEA 2025.2, Qodana for JVM 2025.2,

Last modified: 18 September 2025