tchigher / shedlock

Distributed lock for your scheduled tasks

ShedLock

ShedLock does one and only one thing. It makes sure 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 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. 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.

• Usage
• Lock Providers
  • Mongo
  • DynamoDB
  • JdbcTemplate
  • ZooKeeper (using Curator)
  • Redis (using Spring RedisConnectionFactory)
  • Redis (using Jedis)
  • Hazelcast
  • Couchbase
  • ElasticSearch
  • CosmosDB
• Running without Spring
• Troubleshooting
• Modes of Spring integration
  • TaskScheduler proxy
  • Scheduled method proxy
• Versions

Usage

To use ShedLock, you do the following

1. Enable and configure Scheduled locking
2. Annotate your scheduled tasks
3. Configure a Lock Provider

Enable and configure Scheduled locking

First of all we have to import the project

<dependency>
    <groupId>net.javacrumbs.shedlock</groupId>
    <artifactId>shedlock-spring</artifactId>
    <version>3.0.0</version>
</dependency>

Now we need to integrate the library into Spring. In order to enable schedule locking use @EnableSchedulerLock annotation

@Configuration
@EnableScheduling
@EnableSchedulerLock(defaultLockAtMostFor = "PT30S")
class MySpringConfiguration {
    ...
}

Annotate your scheduled tasks

import net.javacrumbs.shedlock.core.SchedulerLock;

...

@Scheduled(...)
@SchedulerLock(name = "scheduledTaskName")
public void scheduledTask() {
   // do something
}

The @SchedulerLock annotation has several purposes. First of all, only annotated methods are locked, the library ignores all other scheduled tasks. You also have to specify the name for the lock. Only one tasks with the same name can be executed at the same time.

You can also set lockAtMostFor attribute which specifies how long the lock should be kept in case the executing node dies. This is just a fallback, under normal circumstances the lock is released as soon the tasks finishes. You have to set lockAtMostFor to a value which is much longer than normal execution time. If the task takes longer than lockAtMostFor the resulting behavior may be unpredictable (more processes will effectively hold the lock).

Lastly, you can set lockAtLeastFor attribute 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.

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 such case, you can configure it like this

import net.javacrumbs.shedlock.core.SchedulerLock;

...
private static final String FOURTEEN_MIN = "PT14M";
...

@Scheduled(cron = "0 */15 * * * *")
@SchedulerLock(name = "scheduledTaskName", lockAtMostForString = FOURTEEN_MIN, lockAtLeastForString = FOURTEEN_MIN)
public void scheduledTask() {
   // do something
}

By setting lockAtMostFor we make sure that the lock is released even if the node dies and 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 for a 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.

Mongo

Import the project

<dependency>
    <groupId>net.javacrumbs.shedlock</groupId>
    <artifactId>shedlock-provider-mongo</artifactId>
    <version>3.0.0</version>
</dependency>

Configure:

import net.javacrumbs.shedlock.provider.mongo.MongoLockProvider;

...

@Bean
public LockProvider lockProvider(MongoClient mongo) {
    return new MongoLockProvider(mongo, "databaseName");
}

Please note that MongoDB integration requires Mongo >= 2.4 and mongo-java-driver >= 3.4.0

DynamoDB

Import the project

<dependency>
   <groupId>net.javacrumbs.shedlock</groupId>
   <artifactId>shedlock-provider-dynamodb</artifactId>
   <version>3.0.0</version>
</dependency>

Configure:

import net.javacrumbs.shedlock.provider.dynamodb.DynamoDBLockProvider;

...

@Bean
public LockProvider lockProvider(com.amazonaws.services.dynamodbv2.document.DynamoDB dynamoDB) {
   return new DynamoDBLockProvider(dynamoDB.getTable("existingTableName"));
}

Please note that the lock table must be created externally. DynamoDBUtils#createLockTable may be used for creating it programmatically. A table definition is available from DynamoDBLockProvider's Javadoc.

JdbcTemplate

There are two lock providers based on JDBC. JdbcTemplateLockProvider which uses Spring's JDBC template, supports transactions etc, and plain JdbcLockProvider which asseses JDBC directly. They should work more or less the same, if in doubt, use JdbcTemplateLockProvider.

First, create the table (please note that name has to be primary key)

CREATE TABLE shedlock(
    name VARCHAR(64), 
    lock_until TIMESTAMP(3) NULL, 
    locked_at TIMESTAMP(3) NULL, 
    locked_by  VARCHAR(255), 
    PRIMARY KEY (name)
) 

script for MS SQL is here and for Oracle here

Add dependency

<dependency>
    <groupId>net.javacrumbs.shedlock</groupId>
    <artifactId>shedlock-provider-jdbc-template</artifactId>
    <version>3.0.0</version>
</dependency>

Configure:

import net.javacrumbs.shedlock.provider.jdbctemplate.JdbcTemplateLockProvider;

...

@Bean
public LockProvider lockProvider(DataSource dataSource) {
    return new JdbcTemplateLockProvider(dataSource);
}

Tested with MySql, Postgres and HSQLDB, should work on all other JDBC compliant databases.

Warning

Do not manually delete lock row or document from DB table. ShedLock has an in-memory cache of existing locks 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. Since 1.0.0 you can clean the cache by calling clearCache() on LockProvider.

ZooKeeper (using Curator)

Import

<dependency>
    <groupId>net.javacrumbs.shedlock</groupId>
    <artifactId>shedlock-provider-zookeeper-curator</artifactId>
    <version>3.0.0</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>3.0.0</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);
}

If you have dependency on spring-data-redis 2 use ShedLock 1.x.x, if you have dependency on spring-data-redis 1 use ShedLock 0.x.x. Please note that there is a bug #105 when ShedLock is used with spring-data-redis 1 so it's recommended to use either spring-data-redis 2 with newest ShedLock or Jedis provider.

Redis (using Jedis)

Import

<dependency>
    <groupId>net.javacrumbs.shedlock</groupId>
    <artifactId>shedlock-provider-redis-jedis</artifactId>
    <version>3.0.0</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-hazelcast</artifactId>
    <version>3.0.0/version>
</dependency>

Configure:

import net.javacrumbs.shedlock.provider.hazelcast.HazelcastLockProvider;

...

@Bean
public HazelcastLockProvider lockProvider(HazelcastInstance hazelcastInstance) {
    return new HazelcastLockProvider(hazelcastInstance);
}

Couchbase

Import the project

<dependency>
    <groupId>net.javacrumbs.shedlock</groupId>
    <artifactId>shedlock-provider-couchbase-javaclient</artifactId>
    <version>3.0.0/version>
</dependency>

Configure:

import net.javacrumbs.shedlock.provider.couchbase.javaclient.CouchbaseLockProvider;

...

@Bean
public CouchbaseLockProvider lockProvider(Bucket bucket) {
    return new CouchbaseLockProvider(bucket);
}

Elasticsearch

I am really not sure that 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-elasticsearch</artifactId>
    <version>3.0.0/version>
</dependency>

Configure:

import static net.javacrumbs.shedlock.provider.elasticsearch.ElasticsearchLockProvider;

...

@Bean
public ElasticsearchLockProvider lockProvider(RestHighLevelClient highLevelClient) {
    return new ElasticsearchLockProvider(highLevelClient);
}

CosmosDB

CosmosDB support is provided by a third-party module available here

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.

Running without Spring

It is possible to use ShedLock without Spring

LockingTaskExecutor executor = new DefaultLockingTaskExecutor(lockProvider);

...

Instant lockAtMostUntil = Instant.now().plusSeconds(600);
executor.executeWithLock(runnable, new LockConfiguration("lockName", lockAtMostUntil));

Modes of Spring integration

ShedLock supports two modes of Spring integration.

TaskScheduler proxy

By default ShedLock creates AOP proxy around Spring TaskScheduler. 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 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.

Scheduled Method proxy

If you have even more special needs, you can use Scheduled Method proxy like this

@EnableSchedulerLock(interceptMode = PROXY_METHOD, defaultLockAtMostFor = "PT30S")

If PROXY_METHOD mode is selected, ShedLock creates AOP proxy around every method with @SchedulerLock annotation. The main advantage of this approach is that it does not depend on Spring scheduling. The disadvantage is that the lock is applied even if you call the method directly. Be also aware, that only void-returning methods are currently supported, an exception is thrown if you annotate and call a method with non-void return type.

Troubleshooting

Help, ShedLock does not do what it's supposed to do!

1. 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.
2. 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.
3. For short-running tasks consider using lockAtLeastFor. If the tasks are short-running, they can be executed one after each other, lockAtLeastFor can prevent it.
4. If you encounter weird error complaining that a Proxy is not class of ThreadPoolTaskScheduler please check lukas-krecan#115 or this StackOverflow quesiton

Requirements and dependencies

• Java 8
• slf4j-api
• Spring Framework (optional)

Versions

Version 1.x.x is compiled and tested with Spring 5 and Spring Data 2. It should be safe to use ShedLock 1.x.x with Spring 4 if you are not using Spring Redis lock provider which introduced incompatibility. In other words

• If you have dependency on spring-data-redis 2 - use ShedLock 1.x.x
• If you have dependency on spring-data-redis 1 - use ShedLock 0.x.x
• In all other cases, you can use both versions, prefereably 1.x.x

Change log

3.0.0

• EnableSchedulerLock.mode renamed to interceptMode
• Use standard Spring AOP configuration to honor Spring Boot config (supports proxyTargetClass flag)
• Removed deprecated SpringLockableTaskSchedulerFactoryBean and related classes
• Removed support for XML configuration

2.6.0

• Updated dependency to Spring 2.1.9
• Support for lock extensions (beta)

2.5.0

• Zookeeper supports lockAtMostFor and lockAtLeastFor params
• Better debug logging

2.4.0

• Fixed potential deadlock in Hazelcast (thanks @HubertTatar)
• Finding class level annotation in proxy method mode (thanks @volkovs)
• ScheduledLockConfigurationBuilder deprecated

2.3.0

• LockProvides is initialized lazilly so it does not change DataSource initialization order

2.2.1

• MongoLockProvider accepts MongoCollection as a constructor param

2.2.0

• DynamoDBLockProvider added

2.1.0

• MongoLockProvider rewritten to use upsert
• ElasticsearchLockProvider added

2.0.1

• AOP proxy and annotation configuration support

1.3.0

• Can set Timezone to JdbcTemplateLock provider

1.2.0

• Support for Couchbase (thanks to @MoranVaisberg)

1.1.1

• Spring RedisLockProvider refactored to use RedisTemplate

1.1.0

• Support for transaction manager in JdbcTemplateLockProvider (thanks to @grmblfrz)

1.0.0

• Upgraded dependencies to Spring 5 and Spring Data 2
• Removed deprecated net.javacrumbs.shedlock.provider.jedis.JedisLockProvider (use net.javacrumbs.shedlock.provider.redis.jedis.JedisLockProvide instead)
• Removed deprecated SpringLockableTaskSchedulerFactory (use ScheduledLockConfigurationBuilder instead)

0.18.2

• ablility to clean lock cache

0.18.1

• shedlock-provider-redis-spring made compatible with spring-data-redis 1.x.x

0.18.0

• Added shedlock-provider-redis-spring (thanks to @siposr)
• shedlock-provider-jedis moved to shedlock-provider-redis-jedis

0.17.0

• Support for SPEL in lock name annotation

0.16.1

• Automatically closing TaskExecutor on Spring shutdown

0.16.0

• Removed spring-test from shedlock-spring compile time dependencies
• Added Automatic-Module-Names

0.15.1

• Hazelcast works with remote cluster

0.15.0

• Fixed ScheduledLockConfigurationBuilder interfaces #32
• Hazelcast code refactoring

0.14.0

• Support for Hazelcast (thanks to @peyo)

0.13.0

• Jedis constructor made more generic (thanks to @mgrzeszczak)

0.12.0

• Support for property placeholders in annotation lockAtMostForString/lockAtLeastForString
• Support for composed annotations
• ScheduledLockConfigurationBuilder introduced (deprecating SpringLockableTaskSchedulerFactory)

0.11.0

• Support for Redis (thanks to @clamey)
• Checking that lockAtMostFor is in the future
• Checking that lockAtMostFor is larger than lockAtLeastFor

0.10.0

• jdbc-template-provider does not participate in task transaction

0.9.0

• Support for @SchedulerLock annotations on proxied classes

0.8.0

• LockableTaskScheduler made AutoClosable so it's closed upon Spring shutdown

0.7.0

• Support for lockAtLeastFor

0.6.0

• Possible to configure defaultLockFor time so it does not have to be repeated in every annotation

0.5.0

• ZooKeeper nodes created under /shedlock by default

0.4.1

• JdbcLockProvider insert does not fail on DataIntegrityViolationException

0.4.0

• Extracted LockingTaskExecutor
• LockManager.executeIfNotLocked renamed to executeWithLock
• Default table name in JDBC lock providers

0.3.0

• @ShedlulerLock.name made obligatory
• @ShedlulerLock.lockForMillis renamed to lockAtMostFor
• Adding plain JDBC LockProvider
• Adding ZooKeepr LockProvider