Events
Question: How can I wait for an event in a job chain?
Introduction
In some cases it is necessary to wait for an event before proceeding with execution.
JobScheduler provides a solution to set off events and to handle these events on an active instance of the eventservice JobScheduler. However it is also possible to check for events in job chains and then conditionally proceed.
You find the complete documentation in scheduler_events.pdf - Documentation. In particular, how to define event handlers with JOE is described in chapter XML Event Handlers (However this should not be needed for the actual example here.)
To demonstrate how to create an event and wait for it in a job chain we will draw up a simple scenario:
- setting up a job to create the event. This is a stand alone job.
- setting up a job chain with a wait step in the middle. When the event arrives, the execution proceeds and the event will be deleted.
- setting up the jobs for deleting and checking the event.
Requirements
The JobScheduler must run using a database. The events are stored permanently in the table "SCHEDULER_EVENTS".
Instructions
- Unzip all files of test_event.zip into the ./config folder of your active instance of the eventservice JobScheduler installation. After unzipping you will have all the objects needed to run the example in the live/test_events subfolder.
- Open the JS operations gui for the workload JobScheduler in your browser using http://scheduler_host:scheduler_port
- Find the {{test_event/job chain_example_wait_for_event }} job chain and click on it.
- There is an order assigned to the job chain. In the order menu press Start order now
- You see the order will run until the step 3 is reached. As the EVENT event does not exist, the order will wait for 10s and then check again.
- Switch to the tab Jobs.
- Find the {{test_event/job_event_add }} job chain and click on it.
- In the Job menu press Start task immediately. This will create the EVENT event.
- Switch to the tab Job Chains.
- See the order proceeding with execution of the next step
How it works
The test_event/job_event_add job is a dummy shell script job with a post processing part. In the post processing the com.sos.jitl.eventing.EventMonitorTaskAfter JITL class is used to add an TEST.TEST_EVENT event.
The test_event/job chain_example_wait_for_event }} job chain has 2 dummy steps and the wait for event step. This step executes the {{test_event/job_event_check job to look for the desired event specified in the scheduler_event_spec parameter. As the events are stored in a xml object you have to specify a xpath expression here.
If the event is not raised, the order executes a setback. The wait time between two checks is configured in the delay_order_after_setback definition of the job (and the job chain node).
After adding the event, the order will proceed with the next step and the event will be removed.
Downloads:
- scheduler events - Documentation
- test_event.zip - job configuration files