@Blocking

The io.smallrye.reactive.messaging.annotations.Blocking annotation can be used on a method annotated with @Incoming, or @Outgoing to indicate that the method should be executed on a worker pool:

@Outgoing("Y")
@Incoming("X")
@Blocking
public String process(String s) {
  return s.toUpperCase();
}

If method execution does not need to be ordered, it can be indicated on the @Blocking annotation:

@Outgoing("Y")
@Incoming("X")
@Blocking(ordered = false)
public String process(String s) {
  return s.toUpperCase();
}

When unordered, the invocation can happen concurrently.

By default, use of @Blocking results in the method being executed in the Vert.x worker pool. If it’s desired to execute methods on a custom worker pool, with specific concurrency needs, it can be defined on @Blocking:

@Outgoing("Y")
@Incoming("X")
@Blocking("my-custom-pool")
public String process(String s) {
  return s.toUpperCase();
}

Specifying the concurrency for the above worker pool requires the following configuration property to be defined:

1	`smallrye.messaging.worker.my-custom-pool.max-concurrency=3`

Supported signatures

@Blocking does not support every signature. The following table lists the supported ones.

Shape	Signature	Comment
Publisher	`@Outgoing("in") @Blocking O generator()`	Invokes the generator from a worker thread. If `ordered` is set to `false`, the generator can be called concurrently.
Publisher	`@Outgoing("in") @Blocking Message<O> generator()`	Invokes the generator from a worker thread. If `ordered` is set to `false`, the generator can be called concurrently.
Processor	`@Incoming("in") @Outgoing("bar") @Blocking O process(I in)`	Invokes the method on a worker thread. If `ordered` is set to `false`, the method can be called concurrently.
Processor	`@Incoming("in") @Outgoing("bar") @Blocking Message<O> process(I in)`	Invokes the method on a worker thread. If `ordered` is set to `false`, the method can be called concurrently.
Subscriber	`@Incoming("in") @Blocking void consume(I in)`	Invokes the method on a worker thread. If `ordered` is set to `false`, the method can be called concurrently.
Subscriber	`@Incoming("in") @Blocking Uni<Void> consume(I in)`	Invokes the method on a worker thread. If `ordered` is set to `false`, the method can be called concurrently.
Subscriber	`@Incoming("in") @Blocking CompletionStage<Void> consume(I in)`	Invokes the method on a worker thread. If `ordered` is set to `false`, the method can be called concurrently.

When a method can be called concurrently, the max concurrency depends on the number of threads from the worker thread pool.

Using io.smallrye.common.annotation.Blocking

io.smallrye.common.annotation.Blocking is another annotation with the same semantic. io.smallrye.common.annotation.Blocking is used by multiple SmallRye projects and Quarkus.

SmallRye Reactive Messaging also supports io.smallrye.common.annotation.Blocking. However, io.smallrye.common.annotation.Blocking does not allow configuring the ordering (it defaults to ordered=true).

When both annotations are used, io.smallrye.reactive.messaging.annotations.Blocking is preferred.