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Quartz.NET and MEF

I have been implementing a scheduler service for several different jobs on several difference schedules, which led me into using Quartz.NET. This is a really nice framework, but since we're using MEF I ran into some issues.

Quartz.NET basically consists of the scheduler engine which runs jobs implementing the IJob interface. The interface simply consists of an Execute method. I export each job with the IJob interface using MEF.

[Export(typeof(IJob))]
public class MyJob : IJob
{
    public void Execute(JobExecutionContext context)
    {
        ...
    }
}


In my scheduler implementation the jobs are imported into an IEnumerable<IJob>.

[ImportMany(typeof(IJob))]
public IEnumerable<IJob> Jobs { get; set; }


The initialization of the scheduled tasks is pretty straight forward. A standard scheduler factory is initialized which in turn gives us a scheduler instance. Each job that was imported by MEF is then added to the scheduler, here with a simple 10 minute trigger just to make things easier.

var factory = new StdSchedulerFactory();
var scheduler = factory.GetScheduler();
foreach (var job in Jobs)
{
    var jobDetail = new JobDetail("Job name", job.GetType());
    var trigger = TriggerUtils.MakeMinutelyTrigger("Trigger name", 10, SimpleTrigger.RepeatIndefinitely);
    scheduler.ScheduleJob(jobDetail, trigger);
}


That is about everything we need to get the jobs going. The issue with MEF however is that each time a job is triggered to run the scheduler creates a new instance of the job. To prevent this behaviour we must create a custom implementation of the scheduler. The IJobFactory interface contains a NewJob method that is run each time a job is about to be run. We would like to return the same instance every time.

public class MefJobFactory : IJobFactory
{
    public IJob NewJob(TriggerFiredBundle bundle)
    {
        try
        {
            var jobs = Bootstrapper.Instance.Container.GetExports<IJob>();
            return jobs.First(job => job.GetType() == bundle.JobDetail.JobType).Value;
        }
        catch (Exception exception)
        {
            throw new SchedulerException("Problem instantiating class " + bundle.JobDetail.JobType, exception);
        }
    }
}


There is one last thing to do to actually implement this custom job factory. Nothing in the code above needs to be changed. All we have to do is to add a few lines to the app.config to instruct Quartz.NET to use our custom implementation instead of the default.

<configuration>
    <configSections>
        <section name="quartz" type="System.Configuration.NameValueSectionHandler, System, Version=1.0.5000.0,Culture=neutral, PublicKeyToken=b77a5c561934e089" />
    </configSections>
    ...
    <quartz>
        <add key="quartz.scheduler.jobFactory.type" value="MyScheduler.MefJobFactory, MyScheduler" />
    </quartz>
</configuration>


And thats it! Instead of creating a new instance of the job on each run, my custom implementation is used to get the MEF exported job.
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