Use unordered executeBlocking for GraphQL blocking resolvers by phillip-kruger · Pull Request #54927 · quarkusio/quarkus

phillip-kruger · 2026-06-18T09:58:48Z

When a blocking GraphQL resolver calls a reactive Vert.x client — such as the imperative Mailer — the resolver can deadlock. The root cause is that BlockingHelper.runBlocking() dispatches blocking resolvers via executeBlocking with a RequestScopedTaskQueue that serializes tasks per-request. The reactive client's event-loop callbacks can't dispatch while the ordered task slot is held, creating a circular wait.

This removes the RequestScopedTaskQueue mechanism and always uses executeBlocking(callable, false) (unordered). This is safe because:

Mutation ordering is already guaranteed by graphql-java's AsyncSerialExecutionStrategy — confirmed by @jmartisk
Query field parallelism is explicitly permitted by the GraphQL spec
The WebSocket handler already uses unordered execution
The gRPC extension had the identical deadlock and fixed it the same way

Not a revert of #54372

This is not a revert of the RequestScopedTaskQueue change (PR #54372). Before that PR, the code used vc.executeBlocking(callable) with no explicit ordering parameter, which defaulted to ordered=true in Vert.x 4 — globally serializing all requests sharing an event loop (the cause of #54361). This PR uses executeBlocking(callable, false) — explicitly unordered — which is a state that never existed before:

State	Code	Cross-request	Within-request	Mailer
Before #54372	`executeBlocking(callable)` — implicit `true`	Serialized (slow)	Serialized	Deadlock
After #54372	`executeBlocking(callable, queue)`	Parallel	Serialized	Deadlock
This PR	`executeBlocking(callable, false)`	Parallel	Parallel	Works

Includes a regression test that sends mail via the imperative Mailer from a @Blocking GraphQL resolver using a real (non-mock) SMTP connection.

Fixes #29141
Fixes #36215

github-actions · 2026-06-18T10:55:39Z

🎊 PR Preview 77c9a79 has been successfully built and deployed to https://quarkus-pr-main-54927-preview.surge.sh/version/main/guides/

Images of blog posts older than 3 months are not available.
Newsletters older than 3 months are not available.

Doogiemuc · 2026-06-18T21:01:05Z

Hello @phillip-kruger ! Thank you so much for looking into this. Only some hours after my comment. I am a senior java developer with more than three decades of coding experience. But what you are writing up there sounds like magic even to me. So once again: KUDOs and I am looking forward to the next quarkus and/GraphQL fix version! 👍

phillip-kruger · 2026-06-18T21:07:41Z

@Doogiemuc what would help is if you can build against this branch and confirm if this solves the issue for you

Doogiemuc · 2026-06-18T21:24:37Z

"build against this branch" Does that mean I would need to build quarkus from source? I'd assume this is a big task that would take me a day just to setup all dependencies. Or do I miss something and there is an easy way?

phillip-kruger · 2026-06-19T00:14:58Z

@Doogiemuc it's fairly easy:

Get a local quarkus: git clone git@github.com:quarkusio/quarkus.git
Then checkout this PR: gh pr checkout 54927 (assuming you have gh cli installed)

Then do https://github.com/quarkusio/quarkus/blob/main/CONTRIBUTING.md#building-main

Once a local version is build you can use that in your app:
https://github.com/quarkusio/quarkus/blob/main/CONTRIBUTING.md#with-maven

cescoffier

I'm ok with this change. I made some comment on the test.

@jponge We had to modify this code heavily for Vert.x 5 - expect the next merge to be chaotic.

jmartisk · 2026-06-19T06:32:29Z

So I'll need a bit more of an explanation here, how is this different from #29306 which I submitted in the past, but it turned out to break Hibernate?

phillip-kruger · 2026-06-19T12:12:49Z

Hi @jmartisk, your PR #29306 was the right fix, the only reason it broke Hibernate was that RequestScopedSessionHolder and RequestScopedStatelessSessionHolder use a HashMap internally, which isn't thread-safe when multiple blocking resolvers run concurrently within the same request. I've now added that fix in this PR as well (switched both to ConcurrentHashMap).

So in short: this PR = your original ordered=false change + the ConcurrentHashMap fix for the Hibernate session holders that was the actual root cause of the breakage.

…urrentHashMap for request-scoped Hibernate session holders

jmartisk · 2026-06-19T12:35:33Z

I also proposed the switch to the ConcurrentHashMap in the previous PR (see #29306 (comment)) but it was considered wrong. CC @Sanne @yrodiere

quarkus-bot · 2026-06-19T12:49:20Z

Status for workflow `Quarkus Documentation CI`

This is the status report for running Quarkus Documentation CI on commit 42ed240.

✅ The latest workflow run for the pull request has completed successfully.

It should be safe to merge provided you have a look at the other checks in the summary.

Warning

There are other workflow runs running, you probably need to wait for their status before merging.

yrodiere · 2026-06-19T12:58:31Z

I also proposed the switch to the ConcurrentHashMap in the previous PR (see #29306 (comment)) but it was considered wrong. CC @Sanne @yrodiere

Indeed. If multiple threads are hitting the same RequestScopedSessionHolder, then you are already in trouble, because they will likely try to use the same session at some point, and that's simply not allowed.

Whatever threads are involved here need to either:

each have their own request context
OR each use its own transaction

EDIT: though if it's supposed to be atomic/consistent DB accesses, as Sanne suggested you would really want to use a single transaction for all this, which would imply a single thread.

Sanne · 2026-06-19T13:06:19Z

It's not quite fair to state "it would break Hibernate". Hibernate could in theory do this, but it's enforcing safety by design - and efficiency I should add: if multiple operations need to happen on the DB, it's a waste of resources to initiate multiple transactional contexts and let them "figure out" any data race condition. It's also extremely error prone as exact impact on the final data representation will become timing dependent, becoming error prone and introducing difficult to reproduce interleavings.

Make an appropriate plan at the client side, decide what it is exactly that needs to happen and send a single coherent plan to the database. Hibernate would help to define such a consistent plan.

quarkus-bot · 2026-06-19T14:26:23Z

Status for workflow `Quarkus CI`

This is the status report for running Quarkus CI on commit 42ed240.

✅ The latest workflow run for the pull request has completed successfully.

It should be safe to merge provided you have a look at the other checks in the summary.

You can consult the Develocity build scans.

Flaky tests - Develocity

⚙️ JVM Integration Tests - JDK 17

📦 integration-tests/hibernate-orm-graphql-panache

❌ io.quarkus.it.hibertnate.orm.graphql.panache.HibernateOrmGraphQLPanacheTest.testEndpoint - History

1 expectation failed. JSON path data.authors.id doesn't match. Expected: iterable containing [<1>] Actual: null - java.lang.AssertionError

Details

java.lang.AssertionError: 
1 expectation failed.
JSON path data.authors.id doesn't match.
Expected: iterable containing [<1>]
  Actual: null

	at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:344)
	at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure.validate(ResponseSpecificationImpl.groovy:516)

⚙️ JVM Integration Tests - JDK 17 Windows

📦 integration-tests/grpc-hibernate

❌ com.example.grpc.hibernate.BlockingRawTest.shouldAdd - History

Condition with Lambda expression in com.example.grpc.hibernate.BlockingRawTestBase was not fulfilled within 30 seconds. - org.awaitility.core.ConditionTimeoutException

Details

org.awaitility.core.ConditionTimeoutException: Condition with Lambda expression in com.example.grpc.hibernate.BlockingRawTestBase was not fulfilled within 30 seconds.
	at org.awaitility.core.ConditionAwaiter.await(ConditionAwaiter.java:167)
	at org.awaitility.core.CallableCondition.await(CallableCondition.java:78)
	at org.awaitility.core.CallableCondition.await(CallableCondition.java:26)
	at org.awaitility.core.ConditionFactory.until(ConditionFactory.java:1160)
	at org.awaitility.core.ConditionFactory.until(ConditionFactory.java:1129)
	at com.example.grpc.hibernate.BlockingRawTestBase.shouldAdd(BlockingRawTestBase.java:59)
	at java.base/java.lang.reflect.Method.invoke(Method.java:569)

📦 integration-tests/hibernate-orm-graphql-panache

❌ io.quarkus.it.hibertnate.orm.graphql.panache.HibernateOrmGraphQLPanacheTest.testEndpoint - History

1 expectation failed. JSON path data.authors.id doesn't match. Expected: iterable containing [<1>] Actual: null - java.lang.AssertionError

Details

java.lang.AssertionError: 
1 expectation failed.
JSON path data.authors.id doesn't match.
Expected: iterable containing [<1>]
  Actual: null

	at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:344)
	at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure.validate(ResponseSpecificationImpl.groovy:516)

⚙️ JVM Integration Tests - JDK 21

📦 integration-tests/hibernate-orm-graphql-panache

❌ io.quarkus.it.hibertnate.orm.graphql.panache.HibernateOrmGraphQLPanacheTest.testEndpoint - History

1 expectation failed. JSON path data.authors.id doesn't match. Expected: iterable containing [<1>] Actual: null - java.lang.AssertionError

Details

java.lang.AssertionError: 
1 expectation failed.
JSON path data.authors.id doesn't match.
Expected: iterable containing [<1>]
  Actual: null

	at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:344)
	at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure.validate(ResponseSpecificationImpl.groovy:516)

1 expectation failed. JSON path data.authors.id doesn't match. Expected: iterable containing [<1>] Actual: null - java.lang.AssertionError

Details

java.lang.AssertionError: 
1 expectation failed.
JSON path data.authors.id doesn't match.
Expected: iterable containing [<1>]
  Actual: null

	at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:344)
	at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure.validate(ResponseSpecificationImpl.groovy:516)

1 expectation failed. JSON path data.books.id doesn't match. Expected: iterable containing [<2>, <3>, <4>, <5>] Actual: null - java.lang.AssertionError

Details

java.lang.AssertionError: 
1 expectation failed.
JSON path data.books.id doesn't match.
Expected: iterable containing [<2>, <3>, <4>, <5>]
  Actual: null

	at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:344)
	at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure.validate(ResponseSpecificationImpl.groovy:516)

⚙️ JVM Integration Tests - JDK 25

📦 integration-tests/hibernate-orm-graphql-panache

❌ io.quarkus.it.hibertnate.orm.graphql.panache.HibernateOrmGraphQLPanacheTest.testEndpoint - History

1 expectation failed. JSON path data.books.id doesn't match. Expected: iterable containing [<2>, <3>, <4>, <5>] Actual: null - java.lang.AssertionError

Details

java.lang.AssertionError: 
1 expectation failed.
JSON path data.books.id doesn't match.
Expected: iterable containing [<2>, <3>, <4>, <5>]
  Actual: null

	at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:344)
	at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure.validate(ResponseSpecificationImpl.groovy:516)

⚙️ JVM Integration Tests - JDK 25 Semeru

📦 integration-tests/hibernate-orm-graphql-panache

❌ io.quarkus.it.hibertnate.orm.graphql.panache.HibernateOrmGraphQLPanacheTest.testEndpoint - History

1 expectation failed. JSON path data.books.id doesn't match. Expected: iterable containing [<2>, <3>, <4>, <5>] Actual: null - java.lang.AssertionError

Details

java.lang.AssertionError: 
1 expectation failed.
JSON path data.books.id doesn't match.
Expected: iterable containing [<2>, <3>, <4>, <5>]
  Actual: null

	at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:344)
	at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure.validate(ResponseSpecificationImpl.groovy:516)

1 expectation failed. JSON path data.books.id doesn't match. Expected: iterable containing [<2>, <3>, <4>, <5>] Actual: null - java.lang.AssertionError

Details

java.lang.AssertionError: 
1 expectation failed.
JSON path data.books.id doesn't match.
Expected: iterable containing [<2>, <3>, <4>, <5>]
  Actual: null

	at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:344)
	at io.restassured.internal.ResponseSpecificationImpl$HamcrestAssertionClosure.validate(ResponseSpecificationImpl.groovy:516)

phillip-kruger temporarily deployed to ci June 18, 2026 09:58 — with GitHub Actions Inactive

quarkus-bot Bot added area/graphql area/smallrye labels Jun 18, 2026

phillip-kruger requested a review from cescoffier June 18, 2026 10:06

phillip-kruger temporarily deployed to ci June 18, 2026 10:13 — with GitHub Actions Inactive

quarkus-bot Bot added the area/hibernate-orm Hibernate ORM label Jun 18, 2026

phillip-kruger force-pushed the fix-graphql-mailer-deadlock branch from bea0293 to 4a3a7b1 Compare June 18, 2026 10:18

phillip-kruger temporarily deployed to ci June 18, 2026 10:18 — with GitHub Actions Inactive

phillip-kruger force-pushed the fix-graphql-mailer-deadlock branch from 4a3a7b1 to 15fcb49 Compare June 19, 2026 00:35

phillip-kruger temporarily deployed to ci June 19, 2026 00:35 — with GitHub Actions Inactive

phillip-kruger requested a review from jmartisk June 19, 2026 00:39

phillip-kruger marked this pull request as ready for review June 19, 2026 00:39

phillip-kruger temporarily deployed to ci June 19, 2026 00:39 — with GitHub Actions Inactive

This comment has been minimized.

Sign in to view

quarkus-bot Bot added the triage/flaky-test label Jun 19, 2026

cescoffier previously approved these changes Jun 19, 2026

View reviewed changes

phillip-kruger dismissed cescoffier’s stale review via d86718d June 19, 2026 12:09

phillip-kruger temporarily deployed to ci June 19, 2026 12:09 — with GitHub Actions Inactive

Use unordered executeBlocking for GraphQL blocking resolvers and Conc…

42ed240

…urrentHashMap for request-scoped Hibernate session holders

phillip-kruger force-pushed the fix-graphql-mailer-deadlock branch from d86718d to 42ed240 Compare June 19, 2026 12:15

phillip-kruger temporarily deployed to ci June 19, 2026 12:16 — with GitHub Actions Inactive

Conversation

phillip-kruger commented Jun 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Not a revert of #54372

Uh oh!

github-actions Bot commented Jun 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Doogiemuc commented Jun 18, 2026

Uh oh!

phillip-kruger commented Jun 18, 2026

Uh oh!

Doogiemuc commented Jun 18, 2026

Uh oh!

phillip-kruger commented Jun 19, 2026

Uh oh!

This comment has been minimized.

This comment has been minimized.

This comment has been minimized.

cescoffier left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

jmartisk commented Jun 19, 2026

Uh oh!

phillip-kruger commented Jun 19, 2026

Uh oh!

jmartisk commented Jun 19, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

quarkus-bot Bot commented Jun 19, 2026

Status for workflow Quarkus Documentation CI

Uh oh!

yrodiere commented Jun 19, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Sanne commented Jun 19, 2026

Uh oh!

quarkus-bot Bot commented Jun 19, 2026 • edited by github-actions Bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Status for workflow Quarkus CI

Flaky tests - Develocity

⚙️ JVM Integration Tests - JDK 17

📦 integration-tests/hibernate-orm-graphql-panache

⚙️ JVM Integration Tests - JDK 17 Windows

📦 integration-tests/grpc-hibernate

📦 integration-tests/hibernate-orm-graphql-panache

⚙️ JVM Integration Tests - JDK 21

📦 integration-tests/hibernate-orm-graphql-panache

⚙️ JVM Integration Tests - JDK 25

📦 integration-tests/hibernate-orm-graphql-panache

⚙️ JVM Integration Tests - JDK 25 Semeru

📦 integration-tests/hibernate-orm-graphql-panache

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants

phillip-kruger commented Jun 18, 2026 •

edited

Loading

github-actions Bot commented Jun 18, 2026 •

edited

Loading

jmartisk commented Jun 19, 2026 •

edited

Loading

Status for workflow `Quarkus Documentation CI`

yrodiere commented Jun 19, 2026 •

edited

Loading

quarkus-bot Bot commented Jun 19, 2026 •

edited by github-actions Bot

Loading

Status for workflow `Quarkus CI`