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Merge pull request #34808 from cescoffier/transactional-and-run-on-vi…
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…rtual-thread

Lift the limitation regarding @transactional and @RunOnVirtualThread
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cescoffier authored Jul 18, 2023
2 parents f278dde + c85d8d6 commit dc120ff
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37 changes: 7 additions & 30 deletions docs/src/main/asciidoc/virtual-threads.adoc
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Expand Up @@ -369,6 +369,9 @@ This `synchronized` block is the culprit.
Replacing it with a lock is a good solution, but it won't be enough: `synchronized` blocks are also used in `executeWithFlags(int flag)`.
A systematic review of the postgresql-jdbc driver is necessary to make sure that it is compliant with virtual threads.

NOTE: Recent versions of the Postgresql driver and MariaDB driver remove the pinning.
However, pinning may still happen because of the rest of the stack.

=== Reactive drivers at the rescue
The vertx-sql-client is a reactive client, hence it is not supposed to block while waiting for the completion of a
transaction with the database.
Expand Down Expand Up @@ -437,30 +440,6 @@ of thousands of threads.
You can refer to link:https://mail.openjdk.org/pipermail/loom-dev/2022-July/004844.html[this mail] to get more information
on how we envision our future with virtual threads.

=== Our solution to the Netty problem
In order to avoid this wasting of resource without modifying Netty upstream, we wrote an extension that modifies the
bytecode of the class responsible for creating the thread locals at build time.
Using this extension, performance of virtual threads in Quarkus for the Json Serialization test of the Techempower suite
increased by nearly 80%, making it almost as good as reactive endpoints.

To use it, it needs to be added as a dependency:

[source,xml,role="primary asciidoc-tabs-target-sync-cli asciidoc-tabs-target-sync-maven"]
.pom.xml
----
<dependency>
<groupId>io.quarkus</groupId>
<artifactId>quarkus-netty-loom-adaptor</artifactId>
</dependency>
----

Furthermore, some operations undertaken by this extension need special access, it is necessary to

- compile the application with the flag `-Dnet.bytebuddy.experimental`
- open the `java.base.lang` module at runtime with the flag `--add-opens java.base/java.lang=ALL-UNNAMED`

This extension is only intended to improve performance, it is perfectly fine not to use it.

=== Concerning dev mode
If you want to use quarkus with the dev mode, it won't be possible to manually specify the flags we mentioned along this guide.
Instead, you want to specify them all in the configuration of the `quarkus-maven-plugin` as presented below.
Expand All @@ -481,11 +460,10 @@ Instead, you want to specify them all in the configuration of the `quarkus-maven
</executions>
<configuration>
<source>19</source>
<target>19</target>
<source>20</source>
<target>20</target>
<compilerArgs>
<arg>--enable-preview</arg>
<arg>-Dnet.bytebuddy.experimental</arg>
</compilerArgs>
<jvmArgs>--enable-preview --add-opens java.base/java.lang=ALL-UNNAMED</jvmArgs>
</configuration>
Expand All @@ -502,11 +480,10 @@ The configuration of the quarkus-maven-plugin will be simpler:
.pom.xml
----
<configuration>
<source>19</source>
<target>19</target>
<source>20</source>
<target>20</target>
<compilerArgs>
<arg>--enable-preview</arg>
<arg>-Dnet.bytebuddy.experimental</arg>
</compilerArgs>
<jvmArgs>--enable-preview</jvmArgs>
</configuration>
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Original file line number Diff line number Diff line change
Expand Up @@ -822,13 +822,6 @@ private boolean isRunOnVirtualThread(MethodInfo info, BlockingDefault defaultVal
Map.Entry<AnnotationTarget, AnnotationInstance> runOnVirtualThreadAnnotation = getInheritableAnnotation(info,
RUN_ON_VIRTUAL_THREAD);

//should the Transactional annotation override the annotation @RunOnVirtualThread ?
//here it does : it is impossible for a transaction to run on a virtual thread
Map.Entry<AnnotationTarget, AnnotationInstance> transactional = getInheritableAnnotation(info, TRANSACTIONAL); //we treat this the same as blocking, as JTA is blocking, but it is lower priority
if (transactional != null) {
return false;
}

if (runOnVirtualThreadAnnotation != null) {
if (!JDK_SUPPORTS_VIRTUAL_THREADS) {
throw new DeploymentException("Method '" + info.name() + "' of class '" + info.declaringClass().name()
Expand Down Expand Up @@ -894,15 +887,14 @@ private boolean isBlocking(MethodInfo info, BlockingDefault defaultValue) {
return false;
}
Map.Entry<AnnotationTarget, AnnotationInstance> transactional = getInheritableAnnotation(info, TRANSACTIONAL); //we treat this the same as blocking, as JTA is blocking, but it is lower priority
if (transactional != null) {
return true;
}
if (defaultValue == BlockingDefault.BLOCKING) {
return true;
} else if (defaultValue == BlockingDefault.RUN_ON_VIRTUAL_THREAD) {
return false;
} else if (defaultValue == BlockingDefault.NON_BLOCKING) {
return false;
} else if (transactional != null) {
return true;
}
return doesMethodHaveBlockingSignature(info);
}
Expand Down

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