Merge pull request quarkusio#34913 from cescoffier/virtual-thread-doc

docs/src/main/asciidoc/resteasy-reactive-virtual-threads.adoc

@@ -0,0 +1,316 @@
+////
+This guide is maintained in the main Quarkus repository
+and pull requests should be submitted there:
+https://github.com/quarkusio/quarkus/tree/main/docs/src/main/asciidoc
+////
+[[resteasy-reactive-virtual-threads]]
+= Use virtual threads in REST applications
+include::_attributes.adoc[]
+:diataxis-type: howto
+:categories: web, core
+:summary: How to use virtual threads in a REST application
+
+In this guide, we see how you can use virtual threads in a REST application.
+Because virtual threads are all about I/O, we will also use the REST client.
+
+== Prerequisites
+
+include::{includes}/prerequisites.adoc[]
+
+== Architecture
+
+The application built into this guide is quite simple.
+It calls a weather service for two cities (Valence, France, and Athens, Greece) and decides the best place based on the current temperature.
+
+
+== Create the Maven project
+
+First, we need a new project. Create a new project with the following command:
+
+:create-app-artifact-id: rest-virtual-threads
+:create-app-extensions: resteasy-reactive-jackson,quarkus-rest-client-reactive-jackson
+include::{includes}/devtools/create-app.adoc[]
+
+This command generates a new project importing the RESTEasy Reactive, Reactive REST client, and https://github.com/FasterXML/jackson[Jackson] extensions,
+and in particular, adds the following dependencies:
+
+[source,xml,role="primary asciidoc-tabs-target-sync-cli asciidoc-tabs-target-sync-maven"]
+.pom.xml
+----
+<dependency>
+  <groupId>io.quarkus</groupId>
+  <artifactId>quarkus-resteasy-reactive-jackson</artifactId>
+</dependency>
+<dependency>
+  <groupId>io.quarkus</groupId>
+  <artifactId>quarkus-rest-client-reactive-jackson</artifactId>
+</dependency>
+----
+
+[source,gradle,role="secondary asciidoc-tabs-target-sync-gradle"]
+.build.gradle
+----
+implementation("io.quarkus:quarkus-resteasy-reactive-jackson")
+implementation("quarkus-rest-client-reactive-jackson")
+----
+
+[NOTE]
+====
+You might wonder why we use _reactive_ extensions.
+Virtual threads have limitations, and we can only integrate them properly when using the reactive extensions.
+No worries: your code will be written 100% in a synchronous / imperative style.
+
+Check the xref:./virtual-threads.adoc#why-not[virtual thread reference guide] for details.
+====
+
+== Prepare the `pom.xml` file
+
+We need to customize the `pom.xml` file to use virtual threads.
+
+1) Locate the line with `<maven.compiler.release>17</maven.compiler.release>`, and replace it with:
+
+[source, xml]
+----
+    <maven.compiler.release>20</maven.compiler.release>
+----
+
+2) In the maven-compiler-plugin configuration, add the `--enable-preview` arg (only if you use Java 19 or Java 20)
+
+[source, xml]
+----
+<plugin>
+  <artifactId>maven-compiler-plugin</artifactId>
+  <version>${compiler-plugin.version}</version>
+  <configuration>
+    <compilerArgs>
+      <arg>-parameters</arg>
+      <arg>--enable-preview</arg> <!-- Added line -->
+    </compilerArgs>
+  </configuration>
+</plugin>
+----
+
+3) In the maven-surefire-plugin and maven-failsafe-plugin configurations, add the following `argLine` parameter:
+
+[source, xml]
+----
+<plugin>
+  <artifactId>maven-surefire-plugin</artifactId>
+  <version>${surefire-plugin.version}</version>
+  <configuration>
+    <systemPropertyVariables>
+      <java.util.logging.manager>org.jboss.logmanager.LogManager</java.util.logging.manager>
+      <maven.home>${maven.home}</maven.home>
+    </systemPropertyVariables>
+    <argLine>--enable-preview -Djdk.tracePinnedThreads</argLine> <!-- Added line -->
+  </configuration>
+</plugin>
+<plugin>
+  <artifactId>maven-failsafe-plugin</artifactId>
+  <version>${surefire-plugin.version}</version>
+  <executions>
+    <execution>
+      <goals>
+        <goal>integration-test</goal>
+        <goal>verify</goal>
+      </goals>
+      <configuration>
+        <systemPropertyVariables>
+          <native.image.path>${project.build.directory}/${project.build.finalName}-runner</native.image.path>
+          <java.util.logging.manager>org.jboss.logmanager.LogManager</java.util.logging.manager>
+          <maven.home>${maven.home}</maven.home>
+        </systemPropertyVariables>
+        <argLine>--enable-preview -Djdk.tracePinnedThreads</argLine> <!-- Added line -->
+      </configuration>
+    </execution>
+  </executions>
+</plugin>
+----
+
+
+The `-Djdk.tracePinnedThreads` will detect pinned carrier threads while running tests (See xref:./virtual-threads.adoc#pinning[the virtual thread reference guide for details]).
+
+[IMPORTANT]
+.--enable-preview and Java 21
+====
+The `--enable-preview` flag is only required if you use Java 19 or 20.
+====
+
+== Create the weather client
+
+This section is not about virtual threads.
+Because we need to do some I/O to demonstrate virtual threads usage, we need a client doing I/O operations.
+In addition, the reactive REST client is virtual thread friendly: it does not pin and handle propagation correctly.
+
+Create the `src/main/java/org/acme/WeatherService.java` class with the following content:
+
+[source, java]
+----
+package org.acme;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import io.quarkus.rest.client.reactive.ClientQueryParam;
+import jakarta.ws.rs.GET;
+import org.eclipse.microprofile.rest.client.inject.RegisterRestClient;
+import org.jboss.resteasy.reactive.RestQuery;
+
+@RegisterRestClient(baseUri = "https://api.open-meteo.com/v1/forecast")
+public interface WeatherService {
+
+    @GET
+    @ClientQueryParam(name = "current_weather", value = "true")
+    WeatherResponse getWeather(@RestQuery double latitude, @RestQuery double longitude);
+
+
+    record WeatherResponse(@JsonProperty("current_weather") Weather weather) {
+        // represents the response
+    }
+
+    record Weather(double temperature, double windspeed) {
+        // represents the inner object
+    }
+}
+----
+
+This class models the HTTP interaction with the weather service.
+Read more about the rest client in the dedicated xref:./rest-client-reactive.adoc[guide].
+
+== Create the HTTP endpoint
+
+Now, create the `src/main/java/org/acme/TheBestPlaceToBeResource.java` class with the following content:
+
+[source, java]
+----
+package org.acme;
+
+import io.smallrye.common.annotation.RunOnVirtualThread;
+import jakarta.ws.rs.GET;
+import jakarta.ws.rs.Path;
+import org.eclipse.microprofile.rest.client.inject.RestClient;
+
+@Path("/")
+public class TheBestPlaceToBeResource {
+
+    static final double VALENCE_LATITUDE = 44.9;
+    static final double VALENCE_LONGITUDE = 4.9;
+
+    static final double ATHENS_LATITUDE = 37.9;
+    static final double ATHENS_LONGITUDE = 23.7;
+
+    @RestClient WeatherService service;
+
+    @GET
+    @RunOnVirtualThread <1>
+    public String getTheBestPlaceToBe() {
+        var valence = service.getWeather(VALENCE_LATITUDE, VALENCE_LONGITUDE).weather().temperature();
+        var athens = service.getWeather(ATHENS_LATITUDE, ATHENS_LONGITUDE).weather().temperature();
+
+        // Advanced decision tree
+        if (valence > athens && valence <= 35) {
+            return "Valence! (" + Thread.currentThread() + ")";
+        } else if (athens > 35) {
+            return "Valence! (" + Thread.currentThread() + ")";
+        } else {
+            return "Athens (" + Thread.currentThread() + ")";
+        }
+    }
+}
+----
+<1> Instructs Quarkus to invoke this method on a virtual thread
+
+== Run the application in dev mode
+
+Make sure that you use OpenJDK and JVM versions supporting virtual thread and launch the _dev mode_ with `./mvnw quarkus:dev`:
+
+[source, shell]
+----
+> java --version
+openjdk 20.0.1 2023-04-18 <1>
+OpenJDK Runtime Environment Temurin-20.0.1+9 (build 20.0.1+9)
+OpenJDK 64-Bit Server VM Temurin-20.0.1+9 (build 20.0.1+9, mixed mode)
+
+> ./mvnw quarkus:dev <2>
+----
+<1> Must be 19+
+<2> Launch the dev mode
+
+Then, in a browser, open http://localhost:8080.
+You should get something like:
+
+[source, text]
+----
+Valence! (VirtualThread[#144]/runnable@ForkJoinPool-1-worker-6)
+----
+
+As you can see, the endpoint runs on a virtual thread.
+
+It's essential to understand what happened behind the scene:
+
+1. Quarkus creates the virtual thread to invoke your endpoint (because of the `@RunOnVirtualThread` annotation).
+2. When the code invokes the rest client, the virtual thread is blocked, BUT the carrier thread is not blocked (that's the virtual thread _magic touch_).
+3. Once the first invocation of the rest client completes, the virtual thread is rescheduled and continues its execution.
+4. The second rest client invocation happens, and the virtual thread is blocked again (but not the carrier thread).
+5. Finally, when the second invocation of the rest client completes, the virtual thread is rescheduled and continues its execution.
+6. The method returns the result. The virtual thread terminates.
+7. The result is captured by Quarkus and written in the HTTP response
+
+== Verify pinning using tests
+
+In the `pom.xml,` we added an `argLine` argument to the surefire and failsafe plugins:
+
+[source, xml]
+----
+<argLine>--enable-preview -Djdk.tracePinnedThreads</argLine>
+----
+
+The `-Djdk.tracePinnedThreads` dumps the stack trace if a virtual thread cannot be _unmounted_ smoothly (meaning that it blocks the carrier thread).
+That's what we call _pinning_ (more info in xref:./virtual-threads.adoc#pinning[the virtual thread reference guide]).
+
+We recommend enabling this flag in tests.
+Thus, you can check that your application behaves correctly when using virtual threads.
+Just check your log after having run the test.
+If you see a stack trace... better check what's wrong.
+If your code (or one of your dependencies) pins, it might be better to use regular worker thread instead.
+
+Create the `src/test/java/org/acme/TheBestPlaceToBeResourceTest.java` class with the following content:
+
+[source, java]
+----
+package org.acme;
+
+import io.quarkus.test.junit.QuarkusTest;
+import io.restassured.RestAssured;
+import org.junit.jupiter.api.Test;
+
+@QuarkusTest
+class TheBestPlaceToBeResourceTest {
+
+    @Test
+    void verify() {
+        RestAssured.get("/")
+                .then()
+                .statusCode(200);
+    }
+
+}
+----
+
+It is a straightforward test, but at least it will detect if our application is pinning.
+Run the test with either:
+
+- `r` in dev mode (using continuous testing)
+- `./mvnw test`
+
+As you will see, it does not pin - no stack trace.
+It is because the reactive REST client is implemented in a virtual-thread-friendly way.
+
+The same approach can be used with integration tests.
+
+== Conclusion
+
+This guide shows how you can use virtual threads with RESTEasy Reactive and the reactive REST client.
+Learn more about virtual threads support on:
+
+- xref:./messaging-virtual-threads.adoc[@RunOnVirtualThread in messaging applications] (this guide covers Apache Kafka)
+- xref:./grpc-virtual-threads.adoc[@RunOnVirtualThread in gRPC services]
+- xref:./virtual-threads.adoc[the virtual thread reference guide] (include native compilation and containerization)

docs/src/main/asciidoc/resteasy-reactive.adoc

@@ -1846,14 +1846,15 @@ how to use it.
 Here are some more advanced topics that you may not need to know about initially, but
 could prove useful for more complex use cases.
 
+[#execution-model-blocking-non-blocking]
 === Execution model, blocking, non-blocking
 
 [[execution-model]]
 
 RESTEasy Reactive is implemented using two main thread types:
 
 - Event-loop threads: which are responsible, among other things, for reading bytes from the HTTP request and
- writing bytes back to the HTTP response
+writing bytes back to the HTTP response
 - Worker threads: they are pooled and can be used to offload long-running operations
 
 The event-loop threads (also called IO threads) are responsible for actually performing all the IO