Jobs and Triggers

Jobs and Triggers are the core of the Quartz library.

Jobs

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

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

When the job's trigger fires, one of the scheduler's worker threads calls Execute(..). The JobExecutionContext passed to it describes the job's run-time environment: the IScheduler that executed it, the Trigger that fired it, the job's IJobDetail object, and a few other items.

Your program creates the IJobDetail when it adds the job to the scheduler. It is the definition of the job instance: property settings for the job, and a JobDataMap that can store state for a given instance of your job class. The next lesson covers it in detail.

Triggers

A trigger fires the execution of a job. To schedule a job, create a trigger and set its properties to the schedule you want. A trigger can have its own JobDataMap, to pass the job parameters specific to that trigger's firings. Quartz has several trigger types; the most used are the simple trigger (interface ISimpleTrigger) and the cron trigger (interface ICronTrigger).

SimpleTrigger is for 'one-shot' execution (a single execution at a given moment), or for firing at a given time and repeating N times with a delay of T between executions, much like 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 for calendar-like schedules, such as "every Friday, at noon" or "at 10:15 on the 10th day of every month". WithCronSchedule supports H (hash) tokens to spread fire times across triggers. See CronTrigger for the syntax, and CronExpressionBuilder to compose an expression without writing the string.

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

RecurrenceTrigger (Quartz 3.18+) is for calendar patterns cron cannot express, such as "every 2nd Monday of the month", "every other week on specific days" or "the last weekday of March each year". It uses RFC 5545 RRULE strings.

var example = TriggerBuilder.Create()
    .WithIdentity("trigger-name", "trigger-group")
    .ForJob("job-name", "job-group")
    .WithRecurrenceSchedule("FREQ=MONTHLY;BYDAY=2MO")
    .Build();

Why Jobs and Triggers?

Quartz separates the schedule (trigger) from the work (job). As a result:

• Jobs can be stored in the scheduler without a trigger, and many triggers can use the same job.
• A job can stay in the scheduler after its triggers have expired, and be rescheduled later without being re-defined.
• A trigger can be modified or replaced without re-defining its job.

Identities

Jobs and triggers get identifying keys (JobKey and TriggerKey) when they are registered with the scheduler. A key has a name and a group; groups organize jobs and triggers into categories such as "reporting jobs" and "maintenance jobs". The name must be unique within the group, and name plus group is the complete key.

More in Lesson 4: More About Jobs & JobDetails and Lesson 5: More About Triggers.