Jobs and Triggers

Jobs and Triggers will be the core tools that you use as a developer working with the Quartz library.

Jobs

A job is a class that implements the IJob interface, which has only one simple method:

namespace Quartz
{
    public interface IJob
    {
        Task Execute(JobExecutionContext context);
    }
}

When the job's trigger fires (more on that in a moment), the Execute(..) method is invoked by one of the scheduler's worker threads. The JobExecutionContext object that is passed to this method provides the job instance with information about its "run-time" environment - a handle to the IScheduler that executed it, a handle to the Trigger that triggered the execution, the job's IJobDetail object, and a few other items.

The IJobDetail object is created by the Quartz.NET client (your program) at the time the job is added to the scheduler. It contains various property settings for the job, as well as a JobDataMap, which can be used to store state information for a given instance of your job class. It is essentially the definition of the job instance, and is discussed in further detail in the next lesson.

Triggers

Trigger objects are used to trigger the execution (or 'firing') of jobs. When you wish to schedule a job, you instantiate a trigger and use its properties to configure the scheduling you wish to have. Triggers may also have a JobDataMap associated with them. - this is useful to passing parameters to a Job that are specific to the firings of the trigger. Quartz ships with a handful of different trigger types, but the most commonly used types are simple trigger (interface ISimpleTrigger) and a cron trigger (interface ICronTrigger).

WARNING

cron is the name of an early Linux command-line utility used to schedule jobs. It developed a specific way of describing how a job runs, however the CronTrigger uses a different format where Quartz expects seconds as the first parameter. More...

SimpleTrigger is handy if you need 'one-shot' execution (just single execution of a job at a given moment in time), or if you need to fire a job at a given time, and have it repeat N times, with a delay of T between executions. This should feel similar to the .NET Timer class.

var example = TriggerBuilder.Create()
    .WithIdentity("trigger-name", "trigger-group")
    .ForJob("job-name", "job-group")
    .WithSimpleSchedule(o =>
    {
        o.WithRepeatCount(5)
            .WithInterval(TimeSpan.FromMinutes(5));
    })
    .Build();

CronTrigger is useful if you wish to have triggering based on calendar-like schedules - such as "every Friday, at noon" or "at 10:15 on the 10th day of every month.". You can use Cron Maker to explore the syntax.

var example = TriggerBuilder.Create()
    .WithIdentity("trigger-name", "trigger-group")
    .ForJob("job-name", "job-group")
    .WithCronSchedule("45 23 * * 6")
    .Build();

Why Jobs and Triggers?

Many job schedulers do not have separate notions of jobs and triggers. Some define a 'job' as simply an execution time (or schedule) along with some small job identifier. Others are much like the union of Quartz's job and trigger objects. While developing Quartz, we decided that it made sense to create a separation between the schedule and the work to be performed on that schedule. This has (in our opinion) many benefits.

For example, Jobs can be created and stored in the job scheduler independent of a trigger, and many triggers can be associated with the same job. Another benefit of this loose-coupling is the ability to configure jobs that remain in the scheduler after their associated triggers have expired, so that that it can be rescheduled later, without having to re-define it. It also allows you to modify or replace a trigger without having to re-define its associated job.

Identities

Jobs and Triggers are given identifying keys as they are registered with the Quartz scheduler. The keys of Jobs and Triggers (JobKey and TriggerKey) allow them to be placed into 'groups' which can be useful for organizing your jobs and triggers into categories such as "reporting jobs" and "maintenance jobs". The name portion of the key of a job or trigger must be unique within the group. The complete key (or identifier) of a job or trigger is the compound of the name and group.

You now have a general idea about what Jobs and Triggers are, you can learn more about them in Lesson 4: More About Jobs & JobDetails and Lesson 5: More About Triggers