Distributed Locking (RFC-44)

RFC-44 compliant distributed locking patterns for Java services.

When to use this skill

• Implementing distributed locking for scheduled jobs
• Migrating from legacy locking mechanisms
• Choosing between PostgreSQL and Redis locking
• Migrating from Fabric8 leader election
• Migrating from incubated in-repo libraries
• When asked to "migrate locks to be RFC-44 compliant"

Skill Contents

Sections

• When to use this skill (L24-L32)
• Quick Start (L55-L97)
• Implementation Options (L98-L108)
• Common Patterns (L109-L131)
• References (L132-L140)
• Related Rules (L141-L144)
• Related Skills (L145-L150)

Available Resources

📚 references/ - Detailed documentation

• lock patterns
• migration workflow
• redis integration
• troubleshooting

---

Quick Start

1. Add Dependencies (PostgreSQL)

# gradle/libs.versions.toml
[versions]
distributed-locking-api = "2.0.0"
distributed-locking-postgres-jooq = "2.0.0"

[libraries]
distributed-locking-api = { module = "com.bitso.commons:distributed-locking-api", version.ref = "distributed-locking-api" }
distributed-locking-postgres-jooq = { module = "com.bitso.commons:distributed-locking-postgres-jooq", version.ref = "distributed-locking-postgres-jooq" }

2. Create Configuration Bean

@Configuration
public class DistributedLockConfiguration {
    @Bean
    DistributedLockManager<Long> distributedLockManager(
            @Qualifier("write-dslcontext") DSLContext dslContext) {
        return new JooqPostgresSessionDistributedLockManager(dslContext);
    }
}

3. Use in Scheduled Jobs

@Scheduled(cron = "${job.cron:-}", zone = "UTC")
public void scheduledJob() {
    try (var lock = distributedLockManager.tryLock("job-lock")) {
        if (!lock.acquired()) {
            log.info("Job already running on another instance");
            return;
        }
        doWork();
    }
}

Implementation Options

RFC-44 supports two valid locking implementations:

Implementation	When to Use
PostgreSQL Advisory Locks (Default)	Services with PostgreSQL available
Redis Locking (Allowed)	Services without PostgreSQL, or with justified Redis use case

Important: Redis-based locking is NOT deprecated. It is explicitly supported per RFC-44.

Common Patterns

Try-with-resources Pattern

try (var lock = distributedLockManager.tryLock("lock-key")) {
    if (!lock.acquired()) {
        return;
    }
    executeTask();
}

Vavr Pattern

Try.withResources(() -> distributedLockManager.tryLock("lock-key"))
    .of(lock -> Option.of(lock)
        .filter(DistributedLock::acquired)
        .onEmpty(() -> log.info("Lock not acquired"))
        .peek(l -> doWork()));

References

Reference	Description
references/migration-workflow.md	Step-by-step migration guide
references/lock-patterns.md	RFC-44 lock patterns
references/redis-integration.md	Redis-based locking setup
references/troubleshooting.md	Common issues and solutions

Related Rules

• java-distributed-locking-rfc44 - Full RFC-44 reference

Related Skills

Skill	Purpose
gradle-standards	Dependency configuration
java-testing	Testing lock mechanisms

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