Application Hangs on Startup Due to Deadlock in DefaultMigrationManager.runSql() with CompletableFuture.join()

[AlekseyMishanin]

🛠 Environment

We’re using the following tech stack in our project:

• Spring Boot: 3.4.10

• Java: 21

• Micrometer Observation: 1.15.4

• Jetty: 12.0.12

⚙️ Configuration

We're configuring the TransactionOutbox bean via the following Spring config class:

@Configuration
@Import({SpringInstantiator.class})
public class TransactionOutboxConfig {

    @Bean
    TransactionOutboxMetrics transactionOutboxMetrics(MeterRegistry registry) {
        return new TransactionOutboxMetrics(registry);
    }

    @Bean
    TransactionOutbox transactionOutbox(DataSourceOutboxTransactionManager transactionManager,
                                        SpringInstantiator springInstantiator,
                                        TransactionOutboxMetrics transactionOutboxMetrics) {

        return TransactionOutbox.builder()
                .instantiator(springInstantiator)
                .transactionManager(transactionManager)
                .persistor(DefaultPersistor.builder()
                        .dialect(Dialect.POSTGRESQL_9)
                        .serializer(JacksonInvocationSerializer.builder()
                                .mapper(txOutboxObjectMapper())
                                .build())
                        .build())
                .listener(transactionOutboxMetrics)
                .build();
    }

    private ObjectMapper txOutboxObjectMapper() {
        return Jackson2ObjectMapperBuilder.json()
                .featuresToDisable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
                .build();
    }
}

🧨 Issue

When starting the application, the process hangs indefinitely. The last output in the logs is:

INFO [main] transactionoutbox.DefaultMigrationManager: Running migration 1: Create outbox table

Full log snapshot:

INFO [main] sentry.SpringBootDefaultSentryConfig: Sentry initialized with version: 0, environment: dev
INFO [main] jetty.JettyServletWebServerFactory: Server initialized with port: 8181
INFO [main] server.Server: jetty-12.0.12; jvm 21.0.8
INFO [main] ContextHandler.application: Initializing Spring embedded WebApplicationContext
INFO [main] context.ServletWebServerApplicationContext: Root WebApplicationContext: initialization completed
INFO [main] hikari.HikariDataSource: main-1 - Start completed.
INFO [main] hikari.HikariDataSource: vpn-1 - Start completed.
INFO [main] transactionoutbox.DefaultMigrationManager: No version record found. Attempting to create
INFO [main] transactionoutbox.DefaultMigrationManager: Created version record.
INFO [main] transactionoutbox.DefaultMigrationManager: Current version is 0, obtained lock
INFO [main] transactionoutbox.DefaultMigrationManager: Running migration 1: Create outbox table

At this point, the application freezes.

🔎 Analysis
Problem Summary

The application hangs during startup in DefaultMigrationManager.runSql() when executing:

CompletableFuture.runAsync(...).join();

Root Cause

A classic deadlock occurs between the Spring bean initialization thread and the asynchronous thread running the migration.

🧵 Thread Dump Summary
🧵 Main Thread (Spring Initialization)

• Status: WAITING for CompletableFuture to complete

• Holds: Spring's AbstractAutowireCapableBeanFactory lock

• Stack:

CompletableFuture.join()
→ DefaultMigrationManager.runSql()
→ DefaultMigrationManager.migrate()
→ TransactionOutboxImpl.initialize()
→ Spring bean initialization

🧵 Thread-11 (Async Executor)

• Status: BLOCKED waiting for Spring's BeanFactory lock

• Wants: To complete transaction inside the migration

• Stack:

AbstractAutowireCapableBeanFactory.getSingletonFactoryBeanForTypeCheck()
→ DataSourceObservationListener.handleGetConnectionBefore()
→ DataSourceTransactionManager.doBegin()
→ txm.inTransactionThrows()
→ DefaultMigrationManager.lambda$runSql$7()
→ CompletableFuture$AsyncRun.run()

🔁 Deadlock Diagram

Main Thread:  [Holds BeanFactory Lock] → [Waits for CompletableFuture]
                                              ↓
Thread-11:    [Waits for BeanFactory Lock] ← [Executing CompletableFuture]

❓ Why This Happens

1. The migration is executed inside a CompletableFuture.runAsync().

2. The main thread calls .join() on this future, while still holding the Spring BeanFactory lock during initialization.

3. The async thread triggers Spring's transaction management (txm.inTransactionThrows()), which involves:

• Micrometer's DataSourceObservationListener

• Bean lookups for observation and tracing

4. This results in an attempt to access the Spring context — which is still locked by the main thread → Deadlock.

✅ Confirmed Workaround

The issue was resolved by excluding DataSourceObservationAutoConfiguration, which prevents the observation system from activating during migration:

spring.autoconfigure.exclude:
  - org.springframework.boot.actuate.autoconfigure.observation.jdbc.DataSourceObservationAutoConfiguration

🙏 Request

Could you please take a look at this? It would be helpful to either:

• Provide an option to disable async execution in DefaultMigrationManager

• Or, delay transactional/observation configuration until after the migration phase

I am happy to provide more diagnostic details or test proposed fixes.

Thanks in advance for your help and the great work on this project!