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ArC: initial documentation of CDI pitfalls with reactive programming #40620

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ArC: initial documentation of CDI pitfalls with reactive programming #40620

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41 changes: 41 additions & 0 deletions docs/src/main/asciidoc/cdi-reference.adoc
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Expand Up @@ -1069,6 +1069,47 @@
}
----

[[reactive_pitfalls]]
== Pitfalls with Reactive Programming

CDI is a purely synchronous framework.

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[Quarkus.Spelling] Use correct American English spelling. Did you really mean 'asynchrony'?

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{"message": "[Quarkus.Spelling] Use correct American English spelling. Did you really mean 'asynchrony'?", "location": {"path": "docs/src/main/asciidoc/cdi-reference.adoc", "range": {"start": {"line": 1075, "column": 36}}}, "severity": "WARNING"}
Its notion of asynchrony is very limited and based solely on thread pools and thread offloading.
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is that the case for async event/observers ?

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Yes. That's the only place in CDI where asynchrony is mentioned, and it's based on thread offloading.

Therefore, there is a number of pitfalls when using CDI together with reactive programming.

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[Quarkus.TermsWarnings] Consider using 'several' rather than 'a number of' unless updating existing content that uses the term.

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{"message": "[Quarkus.TermsWarnings] Consider using 'several' rather than 'a number of' unless updating existing content that uses the term.", "location": {"path": "docs/src/main/asciidoc/cdi-reference.adoc", "range": {"start": {"line": 1077, "column": 3}}}, "severity": "WARNING"}

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=== Detecting When Blocking Is Allowed

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The `io.quarkus.runtime.BlockingOperationControl#isBlockingAllowed()` method can be used to detect whether blocking is allowed on the current thread.
When it is not, and you need to perform a blocking operation, you have to offload it to another thread.

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The easiest way is to use the `Vertx.executeBlocking()` method:

[source,java]
----
import io.quarkus.runtime.BlockingOperationControl;

@ApplicationScoped
public class MyBean {
@Inject
Vertx vertx;

@PostConstruct
void init() {
if (BlockingOperationControl.isBlockingAllowed()) {
somethingThatBlocks();
} else {
vertx.executeBlocking(() -> {
somethingThatBlocks();
return null;
});
}
}

void somethingThatBlocks() {
// use the file system or JDBC, call a REST service, etc.
Thread.sleep(5000);
}
}
----

[[build_time_apis]]
== Build Time Extensions

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