Premise

ActiveMQ Scheduler is a powerful tool for delaying and scheduling asynchronous messages. However, the broker does not currently have the appropriate built in facilities to monitor and manipulate the internal state of the scheduler. I wouldn't want to bloat the broker with ux code anyway, and would prefer to do all of the fancy user stuff outside of the broker process. As long as the broker can forward the scheduled messages in real time to an advisory topic - we can keep a synched state in an external tool. To achieve that we need to create a shim between the broker and the scheduler store that will issue advisory messages. This project is such a shim and forwards all scheduler advisory messages to ActiveMQ.Scheduler.Advisory.

Advisories

Advisories have AMQ_SCHEDULER_ADVISORY header set with the type of advisory.

Type	Description
SCHEDULE	Scheduler is about to schedule a message
SCHEDULED	Scheduler has scheduled a message
DISPATCH	Scheduler is about to dispatch a message
DISPATCHED	Scheduler has dispatched a message
REMOVE	Scheduler is about to remove a previously scheduled message
REMOVED	Scheduler has removed a previously scheduled message
REMOVE_RANGE	Scheduler is about to remove a range previously scheduled messages
REMOVED_RANGE	Scheduler has removed a range of previously scheduled messages

Building

mvn clean package install

Deploying artifact to a local maven repo

Make sure your settings.xml is properly configured.

repositoryId=$(xmllint --xpath '/*[local-name() = "settings"]/*[local = "activeProfile"]/text()' ~/.m2/settings.xml)
repositoryUrl=$(xmllint --xpath '/*[local-name() = "settings"]/*[local-name() = "profiles"]/*[local-name() = "profile" and *[local-name() = "id"]/text() = "$artifactoryId"]' ~/.m2/settings.xml)
version=$(xmllint --xpath '/*[local-name() = "project"]/*[local-name() = "version"]/text()')
mvn deploy:deploy-file -DrepositoryId=$repositoryId -Durl=$repositoryUrl -Dpackaging=jar -DgroupId=org.apache.activemq -DartifactId=activemq-scheduler-store-advisory -Dversion=$version -Dfile=target/activemq-scheduler-store-advisory-$version.jar

Installing

cp target/activemq-scheduler-store-advisory-*.jar /opt/activemq/lib/optional/

Configuring broker

While this is not a well documented feature, broker does allow to specify a custom jobSchedulerStore. By default broker comes with a KahaDb store and a memory store. This example creates a shim between the broker and the KahaDb store.

<broker xmlns="http://activemq.apache.org/schema/core"
            id="broker"
            brokerName="${BROKER_NAME}"
            persistent="true"
            deleteAllMessagesOnStartup="false"
            dataDirectory="${activemq.data}"
            schedulePeriodForDestinationPurge="10000"
            schedulerSupport="true">
	
	<!-- ... -->

	<jobSchedulerStore>
  		<bean xmlns="http://www.springframework.org/schema/beans" 
			id="jobSchedulerStore" 
		  	class="org.apache.activemq.broker.scheduler.advisory.AdvisoryJobSchedulerStore">
	  
    			<constructor-arg ref="broker" />
    			<constructor-arg ref="VirtualTopic.Scheduler.Advisory" />
    			<constructor-arg>
      				<bean xmlns="http://www.springframework.org/schema/beans" 
			      		id="jobSchedulerStoreDelegate" 
		      			class="org.apache.activemq.store.kahadb.scheduler.JobSchedulerStoreImpl">
					<property name="directory" value="${activemq.data}/scheduler" />
      				</bean>
    			</constructor-arg>
	  
  		</bean>
	</jobSchedulerStore>

	<!-- ... -->
	
</broker>