lukas-krecan/ShedLock
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ShedLock
ShedLock makes sure that your scheduled tasks are executed at most once at the same time. If a task is being executed on one node, it acquires a lock which prevents execution of the same task from another node (or thread). Please note, that if one task is already being executed on one node, execution on other nodes does not wait, it is simply skipped.
ShedLock uses an external store like Mongo, JDBC database, Redis, Hazelcast, ZooKeeper or others for coordination.
Feedback and pull-requests welcome!
ShedLock is not a distributed scheduler
Please note that ShedLock is not and will never be full-fledged scheduler, it's just a lock. If you need a distributed scheduler, please use another project (db-scheduler, JobRunr). ShedLock is designed to be used in situations where you have scheduled tasks that are not ready to be executed in parallel, but can be safely executed repeatedly. Moreover, the locks are time-based and ShedLock assumes that clocks on the nodes are synchronized.
- Components
- Usage
- Lock Providers
- JdbcTemplate
- R2DBC
- jOOQ
- Micronaut Data Jdbc
- Mongo
- DynamoDB 2
- ZooKeeper (using Curator)
- Redis (using Spring RedisConnectionFactory)
- Redis (using Spring ReactiveRedisConnectionFactory)
- Redis (using Jedis)
- Hazelcast
- Couchbase
- ElasticSearch
- OpenSearch
- CosmosDB
- Cassandra
- ArangoDB
- Neo4j
- Etcd
- Apache Ignite
- In-Memory
- Memcached
- Datastore
- Firestore
- GCS
- S3
- NATS Jetstream
- Multi-tenancy
- Customization
- Duration specification
- Extending the lock
- Micronaut integration
- CDI integration
- Locking without a framework
- Troubleshooting
- Micrometer integration (Spring)
- Modes of Spring integration
- Scheduled method proxy
- TaskScheduler proxy
- Compatibility matrix
- Release notes
Components
Shedlock consists of three parts
- Core - The locking mechanism
- Integration - integration with your application, using Spring AOP, Micronaut AOP or manual code
- Lock provider - provides the lock using an external process like SQL database, Mongo, Redis and others
Usage
To use ShedLock, you do the following
- Enable and configure Scheduled locking
- Annotate your scheduled tasks
- Configure a Lock Provider
Enable and configure Scheduled locking (Spring)
First of all, we have to import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-spring</artifactId>
<version>7.7.0</version>
</dependency>
Now we need to integrate the library with Spring. In order to enable schedule locking use @EnableSchedulerLock annotation
@Configuration
@EnableScheduling
@EnableSchedulerLock(defaultLockAtMostFor = "10m")
class MySpringConfiguration {
...
}
Annotate your scheduled tasks
import net.javacrumbs.shedlock.spring.annotation.SchedulerLock;
...
@Scheduled(...)
@SchedulerLock(name = "scheduledTaskName")
public void scheduledTask() {
// To assert that the lock is held (prevents misconfiguration errors)
LockAssert.assertLocked();
// do something
}
Behavior
- Only methods annotated by
@SchedulerLockare locked, the library ignores all other scheduled tasks. By default, the lock will be applied even if the method is called directly, not only through the scheduler. - Only one task with the same name can be executed at the same time.
- If the lock is being held by a task, other tasks protected by the same lock are not blocked, but are simply skipped.
- The lock is released as soon as the task is finished (unless
lockAtLeastForis specified, see below) - If the JVM crashes before the task finishes,
lockAtMostForattribute comes to play. The lock is always released afterlockAtMostFor. You have to setlockAtMostForto a value which is much longer than normal execution time. If the task takes longer thanlockAtMostForthe resulting behavior may be unpredictable (more than one process will effectively hold the lock). - If you don't specify
lockAtMostForin@SchedulerLock, the default value from@EnableSchedulerLockwill be used. - You can set
lockAtLeastForattribute which specifies minimum amount of time for which the lock should be kept. Its main purpose is to prevent execution from multiple nodes in case of really short tasks and clock difference between the nodes. - All the annotations support Spring Expression Language (SpEL).
- By default, the lock will be applied even if the method is called directly, not just through the scheduler.
Example
Let's say you have a task which you execute every 15 minutes and which usually takes few minutes to run. Moreover, you want to execute it at most once per 15 minutes. In that case, you can configure it like this:
import net.javacrumbs.shedlock.spring.annotation.SchedulerLock;
@Scheduled(cron = "0 */15 * * * *")
@SchedulerLock(name = "scheduledTaskName", lockAtMostFor = "14m", lockAtLeastFor = "14m")
public void scheduledTask() {
// do something
}
By setting lockAtMostFor we make sure that the lock is released even if the node dies. By setting lockAtLeastFor
we make sure it's not executed more than once in fifteen minutes.
Please note that lockAtMostFor is just a safety net in case that the node executing the task dies, so set it to
a time that is significantly larger than maximum estimated execution time. If the task takes longer than lockAtMostFor,
it may be executed again and the results will be unpredictable (more processes will hold the lock).
Configure LockProvider
There are several implementations of LockProvider.
JdbcTemplate
First, create lock table (please note that name has to be primary key)
# MySQL, MariaDB
CREATE TABLE shedlock(name VARCHAR(64) NOT NULL, lock_until TIMESTAMP(3) NOT NULL,
locked_at TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3), locked_by VARCHAR(255) NOT NULL, PRIMARY KEY (name));
# Postgres
CREATE TABLE shedlock(name VARCHAR(64) NOT NULL, lock_until TIMESTAMP NOT NULL,
locked_at TIMESTAMP NOT NULL, locked_by VARCHAR(255) NOT NULL, PRIMARY KEY (name));
# Oracle
CREATE TABLE shedlock(name VARCHAR(64) NOT NULL, lock_until TIMESTAMP(3) NOT NULL,
locked_at TIMESTAMP(3) NOT NULL, locked_by VARCHAR(255) NOT NULL, PRIMARY KEY (name));
# MS SQL
CREATE TABLE shedlock(name VARCHAR(64) NOT NULL, lock_until datetime2 NOT NULL,
locked_at datetime2 NOT NULL, locked_by VARCHAR(255) NOT NULL, PRIMARY KEY (name));
# DB2
CREATE TABLE shedlock(name VARCHAR(64) NOT NULL PRIMARY KEY, lock_until TIMESTAMP NOT NULL,
locked_at TIMESTAMP NOT NULL, locked_by VARCHAR(255) NOT NULL);
Or use this liquibase change-set.
Add dependency
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-jdbc-template</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.jdbctemplate.JdbcTemplateLockProvider;
...
@Bean
public LockProvider lockProvider(DataSource dataSource) {
return new JdbcTemplateLockProvider(
JdbcTemplateLockProvider.Configuration.builder()
.withJdbcTemplate(new JdbcTemplate(dataSource))
.usingDbTime() // Works on Postgres, MySQL, MariaDb, MS SQL, Oracle, DB2, HSQL and H2
.build()
);
}
By specifying usingDbTime() the lock provider will use UTC time based on the DB server clock.
If you do not specify this option, clock from the app server will be used (the clocks on app servers may not be
synchronized thus leading to various locking issues).
It's strongly recommended to use usingDbTime() option as it uses DB engine specific SQL that prevents INSERT conflicts.
See more details here.
For more fine-grained configuration use other options of the Configuration object
new JdbcTemplateLockProvider(builder()
.withTableName("shdlck")
.withColumnNames(new ColumnNames("n", "lck_untl", "lckd_at", "lckd_by"))
.withJdbcTemplate(new JdbcTemplate(getDatasource()))
.withLockedByValue("my-value")
.withDbUpperCase(true)
.build())
If you need to specify a schema, you can set it in the table name using the usual dot notation
new JdbcTemplateLockProvider(datasource, "my_schema.shedlock")
To use a database with case-sensitive table and column names, the .withDbUpperCase(true) flag can be used.
Default is false (lowercase).
Warning
Do not manually delete lock row from the DB table. ShedLock has an in-memory cache of existing lock rows so the row will NOT be automatically recreated until application restart. If you need to, you can edit the row/document, risking only that multiple locks will be held.
R2DBC
If you are really brave, you can try experimental R2DBC support. Please keep in mind that the capabilities of this lock provider are really limited and that the whole ecosystem around R2DBC is in flux and may easily break.
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-r2dbc</artifactId>
<version>7.7.0</version>
</dependency>
and use it.
@Override
protected LockProvider getLockProvider() {
return new R2dbcLockProvider(connectionFactory);
}
I recommend using R2DBC connection pool.
jOOQ lock provider
First, create lock table as described in the JdbcTemplate section above.
Add dependency
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-jooq</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.jooq.JooqLockProvider;
...
@Bean
public LockProvider getLockProvider(DSLContext dslContext) {
return new JooqLockProvider(dslContext);
}
jOOQ provider has a bit different transactional behavior. While the other JDBC lock providers create new transaction (with REQUIRES_NEW), jOOQ does not support setting it. ShedLock tries to create a new transaction, but depending on your set-up, ShedLock DB operations may end-up being part of the enclosing transaction.
If you need to configure the table name, schema or column names, you can use jOOQ render mapping as described here.
Exposed lock provider
First, create lock table as described in the JdbcTemplate section above.
Add dependency
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-exposed</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.exposed.ExposedLockProvider
...
@Bean
fun getLockProvider(database: Database) = ExposedLockProvider(database)
Micronaut Data Jdbc
If you are using Micronaut data, and you do not want to add dependency on Spring JDBC, you can use Micronaut JDBC support. Just be aware that it has just a basic functionality when compared to the JdbcTemplate provider.
First, create lock table as described in the JdbcTemplate section above.
Add dependency
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-jdbc-micronaut</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.jdbc.micronaut.MicronautJdbcLockProvider;
...
@Singleton
public LockProvider lockProvider(TransactionOperations<Connection> transactionManager) {
return new MicronautJdbcLockProvider(transactionManager);
}
Mongo
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-mongo</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.mongo.MongoLockProvider;
...
@Bean
public LockProvider lockProvider(MongoClient mongo) {
return new MongoLockProvider(mongo.getDatabase(databaseName));
}
Please note that MongoDB integration requires Mongo >= 2.4 and mongo-java-driver >= 3.7.0
Reactive Mongo
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-mongo-reactivestreams</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.mongo.reactivestreams.ReactiveStreamsMongoLockProvider;
...
@Bean
public LockProvider lockProvider(MongoClient mongo) {
return new ReactiveStreamsMongoLockProvider(mongo.getDatabase(databaseName));
}
Please note that MongoDB integration requires Mongo >= 4.x and mongodb-driver-reactivestreams 1.x
DynamoDB 2
Depends on AWS SDK v2.
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-dynamodb2</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.dynamodb2.DynamoDBLockProvider;
...
@Bean
public LockProvider lockProvider(software.amazon.awssdk.services.dynamodb.DynamoDbClient dynamoDB) {
return new DynamoDBLockProvider(dynamoDB, "Shedlock");
}
Please note that the lock table must be created externally with
_idas a partition key.DynamoDBUtils#createLockTablemay be used for creating it programmatically. A table definition is available fromDynamoDBLockProvider's Javadoc.
ZooKeeper (using Curator)
Import
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-zookeeper-curator</artifactId>
<version>7.7.0</version>
</dependency>
and configure
import net.javacrumbs.shedlock.provider.zookeeper.curator.ZookeeperCuratorLockProvider;
...
@Bean
public LockProvider lockProvider(org.apache.curator.framework.CuratorFramework client) {
return new ZookeeperCuratorLockProvider(client);
}
By default, nodes for locks will be created under /shedlock node.
Redis (using Spring RedisConnectionFactory)
Import
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-redis-spring</artifactId>
<version>7.7.0</version>
</dependency>
and configure
import net.javacrumbs.shedlock.provider.redis.spring.RedisLockProvider;
import org.springframework.data.redis.connection.RedisConnectionFactory;
...
@Bean
public LockProvider lockProvider(RedisConnectionFactory connectionFactory) {
return new RedisLockProvider(connectionFactory, ENV);
}
Redis (using Spring ReactiveRedisConnectionFactory)
Import
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-redis-spring</artifactId>
<version>7.7.0</version>
</dependency>
and configure
import net.javacrumbs.shedlock.provider.redis.spring.ReactiveRedisLockProvider;
import org.springframework.data.redis.connection.ReactiveRedisConnectionFactory;
...
@Bean
public LockProvider lockProvider(ReactiveRedisConnectionFactory connectionFactory) {
return new ReactiveRedisLockProvider.Builder(connectionFactory)
.environment(ENV)
.build();
}
Redis lock provider uses classical lock mechanism as described here which may not be reliable in case of Redis master failure.
Redis (using Jedis)
Import
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-redis-jedis4</artifactId>
<version>7.7.0</version>
</dependency>
and configure
import net.javacrumbs.shedlock.provider.redis.jedis.JedisLockProvider;
...
@Bean
public LockProvider lockProvider(JedisPool jedisPool) {
return new JedisLockProvider(jedisPool, ENV);
}
Hazelcast
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-hazelcast4</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.hazelcast4.HazelcastLockProvider;
...
@Bean
public HazelcastLockProvider lockProvider(HazelcastInstance hazelcastInstance) {
return new HazelcastLockProvider(hazelcastInstance);
}
Redis (using Lettuce)
Import
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-redis-lettuce</artifactId>
<version>7.7.0</version>
</dependency>
and configure
import net.javacrumbs.shedlock.provider.redis.lettuce.LettuceLockProvider;
...
@Bean
public LockProvider lockProvider(StatefulRedisConnection<String, String> connection) {
return new LettuceLockProvider(connection, ENV);
}
Couchbase
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-couchbase-javaclient3</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.couchbase.javaclient.CouchbaseLockProvider;
...
@Bean
public CouchbaseLockProvider lockProvider(Bucket bucket) {
return new CouchbaseLockProvider(bucket);
}
For Couchbase 3 use shedlock-provider-couchbase-javaclient3 module and net.javacrumbs.shedlock.provider.couchbase3 package.
Elasticsearch
I am really not sure if it's a good idea to use Elasticsearch as a lock provider. But if you have no other choice, you can. Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-elasticsearch9</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.elasticsearch9.ElasticsearchLockProvider;
...
@Bean
public ElasticsearchLockProvider lockProvider(ElasticsearchClient client) {
return new ElasticsearchLockProvider(client);
}
OpenSearch
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-opensearch-java</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.opensearch.java.OpenSearchLockProvider;
...
@Bean
public OpenSearchLockProvider lockProvider(OpenSearchClient openSearchClient) {
return new OpenSearchLockProvider(openSearchClient);
}
CosmosDB
CosmosDB support is provided by a third-party module available here
Cassandra
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-cassandra</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.cassandra.CassandraLockProvider;
import net.javacrumbs.shedlock.provider.cassandra.CassandraLockProvider.Configuration;
...
@Bean
public CassandraLockProvider lockProvider(CqlSession cqlSession) {
return new CassandraLockProvider(Configuration.builder().withCqlSession(cqlSession).withTableName("lock").build());
}
Example for creating default keyspace and table in local Cassandra instance:
CREATE KEYSPACE shedlock with replication={'class':'SimpleStrategy', 'replication_factor':1} and durable_writes=true;
CREATE TABLE shedlock.lock (name text PRIMARY KEY, lockUntil timestamp, lockedAt timestamp, lockedBy text);
Please, note that CassandraLockProvider uses Cassandra driver v4, which is part of Spring Boot since 2.3.
ArangoDB
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-arangodb</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.arangodb.ArangoLockProvider;
...
@Bean
public ArangoLockProvider lockProvider(final ArangoOperations arangoTemplate) {
return new ArangoLockProvider(arangoTemplate.driver().db(DB_NAME));
}
Please, note that ArangoDB lock provider uses ArangoDB driver v6.7, which is part of arango-spring-data in version 3.3.0.
Neo4j
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-neo4j</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.core.LockConfiguration;
...
@Bean
Neo4jLockProvider lockProvider(org.neo4j.driver.Driver driver) {
return new Neo4jLockProvider(driver);
}
Please make sure that neo4j-java-driver version used by shedlock-provider-neo4j matches the driver version used in your
project (if you use spring-boot-starter-data-neo4j, it is probably provided transitively).
Etcd
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-etcd-jetcd</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.etcd.jetcd.EtcdLockProvider;
...
@Bean
public LockProvider lockProvider(Client client) {
return new EtcdLockProvider(client);
}
Apache Ignite
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-ignite</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.ignite.IgniteLockProvider;
...
@Bean
public LockProvider lockProvider(Ignite ignite) {
return new IgniteLockProvider(ignite);
}
In-Memory
If you want to use a lock provider in tests there is an in-Memory implementation.
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-inmemory</artifactId>
<version>7.7.0</version>
<scope>test</scope>
</dependency>
import net.javacrumbs.shedlock.provider.inmemory.InMemoryLockProvider;
...
@Bean
public LockProvider lockProvider() {
return new InMemoryLockProvider();
}
Memcached (using spymemcached)
Please, be aware that memcached is not a database but a cache. It means that if the cache is full, the lock may be released prematurely Use only if you know what you are doing.
Import
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-memcached-spy</artifactId>
<version>7.7.0</version>
</dependency>
and configure
import net.javacrumbs.shedlock.provider.memcached.spy.MemcachedLockProvider;
...
@Bean
public LockProvider lockProvider(net.spy.memcached.MemcachedClient client) {
return new MemcachedLockProvider(client, ENV);
}
P.S.:
Memcached Standard Protocol:
- A key (arbitrary string up to 250 bytes in length. No space or newlines for ASCII mode)
- An expiration time, in
seconds. '0' means never expire. Can be up to 30 days. After 30 days, is treated as a unix timestamp of an exact date. (supportseconds、minutes、days, and less than30days)
Datastore
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-datastore</artifactId>
<version>7.7.0</version>
</dependency>
and configure
import net.javacrumbs.shedlock.provider.datastore.DatastoreLockProvider;
...
@Bean
public LockProvider lockProvider(com.google.cloud.datastore.Datastore datastore) {
return new DatastoreLockProvider(datastore);
}
Firestore
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-firestore</artifactId>
<version>7.7.0</version>
</dependency>
and configure
import net.javacrumbs.shedlock.provider.firestore.FirestoreLockProvider;
...
@Bean
public LockProvider lockProvider(com.google.cloud.firestore.Firestore firestore) {
return new FirestoreLockProvider(firestore);
}
For more fine-grained configuration, you can use the builder:
@Bean
public LockProvider lockProvider(com.google.cloud.firestore.Firestore firestore) {
return new FirestoreLockProvider(
FirestoreLockProvider.Configuration.builder()
.withFirestore(firestore)
.withCollectionName("custom_lock_collection")
.withFieldNames(new FirestoreLockProvider.FieldNames("custom_lock_until", "custom_locked_at", "custom_locked_by"))
.build()
);
}
GCS
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-gcs</artifactId>
<version>7.7.0</version>
</dependency>
and configure
import net.javacrumbs.shedlock.provider.gcs.GcsLockProvider;
...
@Bean
public LockProvider lockProvider(com.google.cloud.storage.Storage storage, String bucketName) {
return new GcsLockProvider(storage, bucketName);
}
For more fine-grained configuration, you can use the builder:
@Bean
public LockProvider lockProvider() {
return new GcsLockProvider(
StorageOptions
.newBuilder()
.setProjectId("<YOUR GCP PROJECT ID>")
.build()
.getService(),
"<YOUR BUCKET NAME>");
}
Spanner
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-spanner</artifactId>
<version>7.7.0</version>
</dependency>
Configure
import net.javacrumbs.shedlock.provider.spanner.SpannerLockProvider;
...
// Basic
@Bean
public LockProvider lockProvider(DatabaseClient databaseClient) {
return new SpannerLockProvider(databaseClient);
}
// Custom host, table and column names
@Bean
public LockProvider lockProvider(DatabaseClient databaseClient) {
var config = SpannerLockProvider.Configuration.builder()
.withDatabaseClient(databaseClient)
.withTableConfiguration(SpannerLockProvider.TableConfiguration.builder()
...
// Custom table and column names
.build())
.withHostName("customHostName")
.build();
return new SpannerLockProvider(config);
}
S3
Import the project
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-s3v2</artifactId>
<version>7.7.0</version>
</dependency>
and configure
import net.javacrumbs.shedlock.provider.s3v2.S3LockProvider;
...
@Bean
public LockProvider lockProvider(S3Client s3Client) {
return new S3LockProvider(s3Client, "BUCKET_NAME");
}
NATS JetStream
The NATS JetStream provider uses a Key-Value (KV) store to manage locks. It operates out of a single, shared bucket named shedlock-locks by default, which is created automatically if it does not exist.
Import the project:
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-provider-jetstream</artifactId>
<version>7.7.0</version>
</dependency>
Configure:
import net.javacrumbs.shedlock.provider.nats.jetstream.NatsJetStreamLockProvider;
import io.nats.client.Connection;
...
@Bean
public LockProvider lockProvider(Connection natsConnection) {
return new NatsJetStreamLockProvider(natsConnection);
}
Multi-tenancy
If you have multi-tenancy use-case you can use a lock provider similar to this one (see the full example)
private static abstract class MultiTenancyLockProvider implements LockProvider {
private final ConcurrentHashMap<String, LockProvider> providers = new ConcurrentHashMap<>();
@Override
public Optional<SimpleLock> lock(LockConfiguration lockConfiguration) {
String tenantName = getTenantName(lockConfiguration);
return providers.computeIfAbsent(tenantName, this::createLockProvider).lock(lockConfiguration);
}
protected abstract LockProvider createLockProvider(String tenantName);
protected abstract String getTenantName(LockConfiguration lockConfiguration);
}
Customization
You can customize the behavior of the library by implementing LockProvider interface. Let's say you want to implement
a special behavior after a lock is obtained. You can do it like this:
public class MyLockProvider implements LockProvider {
private final LockProvider delegate;
public MyLockProvider(LockProvider delegate) {
this.delegate = delegate;
}
@Override
public Optional<SimpleLock> lock(LockConfiguration lockConfiguration) {
Optional<SimpleLock> lock = delegate.lock(lockConfiguration);
if (lock.isPresent()) {
// do something
}
return lock;
}
}
You can see a full example in TrackingLockProviderWrapper
Duration specification
All the annotations where you need to specify a duration support the following formats
- duration+unit -
1s,5ms,5m,1d(Since 4.0.0) - duration in ms -
100(only Spring integration) - ISO-8601 -
PT15M(see Duration.parse() documentation)
Extending the lock
There are some use-cases which require to extend currently held lock. You can use LockExtender in the following way:
LockExtender.extendActiveLock(Duration.ofMinutes(5), ZERO);
Please note that not all lock provider implementations support lock extension.
KeepAliveLockProvider
There is also KeepAliveLockProvider that is able to keep the lock alive by periodically extending it. It can be used by wrapping the original lock provider. My personal opinion is that it should be used only in special cases, it adds more complexity to the library and the flow is harder to reason about so please use moderately.
@Bean
public LockProvider lockProvider(...) {
return new KeepAliveLockProvider(new XyzProvider(...), scheduler);
}
KeepAliveLockProvider extends the lock in the middle of the lockAtMostFor interval. For example, if the lockAtMostFor is 10 minutes the lock is extended every 5 minutes for 10 minutes until the lock is released. Please note that the minimal lockAtMostFor time supported by this provider is 30s. The scheduler is used only for the lock extension, single thread should be enough.
Micronaut integration
Since version 4.0.0, it's possible to use Micronaut framework for integration
Import the project:
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-micronaut4</artifactId>
<version>7.7.0</version>
</dependency>
Configure default lockAtMostFor value (application.yml):
shedlock:
defaults:
lock-at-most-for: 1m
Configure lock provider:
@Singleton
public LockProvider lockProvider() {
... select and configure your lock provider
}
Configure the scheduled task:
@Scheduled(fixedDelay = "1s")
@SchedulerLock(name = "myTask")
public void myTask() {
assertLocked();
...
}
CDI integration
Since version 5.0.0, it's possible to use CDI for integration (tested only with Quarkus)
Import the project:
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-cdi</artifactId>
<version>7.7.0</version>
</dependency>
Configure default lockAtMostFor value (application.properties):
shedlock.defaults.lock-at-most-for=PT30S
Configure lock provider:
@Produces
@Singleton
public LockProvider lockProvider() {
...
}
Configure the scheduled task:
@Scheduled(every = "1s")
@SchedulerLock(name = "myTask")
public void myTask() {
assertLocked();
...
}
The implementation only depends on jakarta.enterprise.cdi-api and microprofile-config-api so it should be
usable in other CDI compatible frameworks, but it has not been tested with anything else than Quarkus. It's
built on top of javax annotation as Quarkus has not moved to Jakarta EE namespace yet.
The support is minimalistic, for example there is no support for expressions in the annotation parameters yet, if you need it, feel free to send a PR.
Locking without a framework
It is possible to use ShedLock without a framework
LockingTaskExecutor executor = new DefaultLockingTaskExecutor(lockProvider);
...
Instant createdAt = Instant.now();
Duration lockAtMostFor = Duration.ofSeconds(60);
Duration lockAtLeastFor = Duration.ZERO;
executor.executeWithLock(runnable, new LockConfiguration(createdAt, "lockName", lockAtMostFor, lockAtLeastFor));
Extending the lock
Some lock providers support extension of the lock. For the time being, it requires manual lock manipulation,
directly using LockProvider and calling extend method on the SimpleLock.
Multiple LockProvider support in Spring
Since version 6.0.0 you can use multiple lock provider implementations. Just define them in your application context
and disambiguate them using @LockProviderToUse("lockProviderBeanName") annotation on method, class or package.
If the annotation is not found, the execution fails in the runtime, not in startup-time. If you need more dynamic resolution
of LockProviders, use a LockProvider wrapper as described in Multi-tenancy.
Micrometer integration (Spring)
ShedLock can publish lock execution metrics via Micrometer. To enable it, add the
shedlock-micrometer dependency and define a MicrometerLockingTaskExecutorListener bean. ShedLock's Spring
integration will detect it automatically and wire it in — no further configuration is required.
<dependency>
<groupId>net.javacrumbs.shedlock</groupId>
<artifactId>shedlock-micrometer</artifactId>
<version>${shedlock.version}</version>
</dependency>
@Bean
public LockingTaskExecutorListener micrometerLockingTaskExecutorListener(MeterRegistry meterRegistry) {
return new MicrometerLockingTaskExecutorListener(meterRegistry);
}
The following meters are registered, all tagged with lock.name:
| Meter | Type | Description |
|---|---|---|
shedlock.lock.attempts | Counter | Total lock acquisition attempts |
shedlock.lock.acquired | Counter | Successful lock acquisitions |
shedlock.lock.not.acquired | Counter | Failed lock acquisitions (lock held elsewhere) |
shedlock.execution.duration | Timer | Task execution time |
shedlock.execution.active | Gauge | Number of currently executing tasks |
To pre-register meters for known lock names (so dashboards show zero rather than missing data before the first
execution), call registerMetricsFor:
@Bean
public LockingTaskExecutorListener micrometerLockingTaskExecutorListener(MeterRegistry meterRegistry) {
MicrometerLockingTaskExecutorListener listener = new MicrometerLockingTaskExecutorListener(meterRegistry);
listener.registerMetricsFor("myLock1", "myLock2");
return listener;
}
Modes of Spring integration
ShedLock supports two modes of Spring integration. One that uses an AOP proxy around scheduled method (PROXY_METHOD) and one that proxies TaskScheduler (PROXY_SCHEDULER)
Scheduled Method proxy
Since version 4.0.0, the default mode of Spring integration is an AOP proxy around the annotated method.
The main advantage of this mode is that it plays well with other frameworks that want to somehow alter the default Spring scheduling mechanism. It also means that the lock is applied even if you call the method directly. If the method returns a value and the lock is held by another process, null or an empty Optional will be returned (primitive return types are not supported).
Final and non-public methods are not proxied so either you have to make your scheduled methods public and non-final or use TaskScheduler proxy.
TaskScheduler proxy (deprecated)
This mode wraps Spring TaskScheduler in an AOP proxy. This mode does not play well with instrumentation libraries
like opentelementry that also wrap TaskScheduler. Please only use it if you know what you are doing.
It can be switched-on like this (PROXY_SCHEDULER was the default method before 4.0.0):
@EnableSchedulerLock(interceptMode = PROXY_SCHEDULER)
If you do not specify your task scheduler, a default one is created for you. If you have special needs, just create a bean implementing TaskScheduler
interface, and it will get wrapped into the AOP proxy automatically.
@Bean
public TaskScheduler taskScheduler() {
return new MySpecialTaskScheduler();
}
Alternatively, you can define a bean of type ScheduledExecutorService and it will automatically get used by the tasks
scheduling mechanism.
Spring XML configuration
Spring XML configuration is not supported as of version 3.0.0. If you need it, please use version 2.6.0 or file an issue explaining why it is needed.
Lock assert
To prevent misconfiguration errors, like AOP misconfiguration, missing annotation etc., you can assert that the lock works by using LockAssert:
@Scheduled(...)
@SchedulerLock(..)
public void scheduledTask() {
// To assert that the lock is held (prevents misconfiguration errors)
LockAssert.assertLocked();
// do something
}
In unit tests you can switch-off the assertion by calling LockAssert.TestHelper.makeAllAssertsPass(true) on given thread (as in this example).
Kotlin gotchas
The library is tested with Kotlin and works fine. The only issue is Spring AOP which does not work on final method. If you use @SchedulerLock with @Component
annotation, everything should work since Kotlin Spring compiler plugin will automatically 'open' the method for you. If @Component annotation is not present, you
have to open the method by yourself. (see this issue for more details)
Caveats
Locks in ShedLock have an expiration time which leads to the following possible issues.
- If the task runs longer than
lockAtMostFor, the task can be executed more than once - If the clock difference between two nodes is more than
lockAtLeastForor minimal execution time the task can be executed more than once.
Troubleshooting
Help, ShedLock does not do what it's supposed to do!
- Upgrade to the newest version
- Use LockAssert to ensure that AOP is correctly configured.
- If it does not work, please read about Spring AOP internals (for example here)
- Check the storage. If you are using JDBC, check the ShedLock table. If it's empty, ShedLock is not properly configured. If there is more than one record with the same name, you are missing a primary key.
- Use ShedLock debug log. ShedLock logs interesting information on DEBUG level with logger name
net.javacrumbs.shedlock. It should help you to see what's going on. - For short-running tasks consider using
lockAtLeastFor. If the tasks are short-running, they could be executed one after another,lockAtLeastForcan prevent it.
Compatibility matrix
| ShedLock Version | Minimal JVM version | Tested with |
|---|---|---|
| 7.x.x | 17 | Spring 7.0, 6.2, Spring Boot 4.x, 3.5, 3.4 Micronaut 4 |
| 6.x.x | 17 | Spring 6.2, 6.1 Spring Boot 3.5, 3.4, 3.3 Micronaut 4 |
| 5.x.x | 17 | Spring 6.1, 6.0 Spring Boot 3.4, 3.3, 3.2 Micronaut 3, 4 |
| 4.x.x | 8 | Spring 6.0, 5.3 Spring Boot 3.0, 2.7, 2.6 |
| 3.x.x | 8 | Spring 5.2, 5.1 Spring Boot 2.2, 2.1 |
| 2.x.x | 8 | Spring 5.1, 5.0 Spring Boot 2.1 |
| 1.x.x | 8 | Spring 5.0 Spring Boot 2.0 |
ShedLock may work with additional versions of the Spring, this table just depicts what it was tested with.
Release notes
See here
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