org.hawkular.metrics.tasks.api

Interface TaskService

All Known Implementing Classes:

TaskServiceImpl

public interface TaskService

The primary API for task scheduling and execution. See TaskServiceBuilder for details on creating and configuring a TaskService. Note that there is currently only support for repeating tasks. Support will be added for non-repeated, single execution tasks.

Author:

jsanda

Method Summary

Modifier and Type	Method and Description
rx.Observable<Task>	scheduleTask(org.joda.time.DateTime time, Task task) Schedules the task for repeated execution starting in the next time slice after time.
void	shutdown() Shuts down the internal scheduler.
void	start() Starts the internal scheduler which takes care of running jobs to process the task queue.

Method Detail

start

void start()

Starts the internal scheduler which takes care of running jobs to process the task queue. This method should be called before any calls to scheduleTask(DateTime, Task).

shutdown

void shutdown()

Shuts down the internal scheduler.

scheduleTask

rx.Observable<Task> scheduleTask(org.joda.time.DateTime time,
                                 Task task)

Schedules the task for repeated execution starting in the next time slice after time. If the task scheduler runs jobs for executing tasks every minute and if time is 13:01:22, then the earliest that the task can first get scheduled to execute is at 13:02 and every minute there after. Execution times are determined by Task.getInterval(). If the task has an interval of 30 minutes, then it would be scheduled to run at 13:30, 14:00, 14:30, and so on.

The task is guaranteed to execute at its scheduled time or later, and only one instance of the task will be executed at a time for a given time slice. In other words, if there are 5 machines running TaskService, only one of those TaskService instances will execute the task for a particular time slice.

If task execution fails for whatever reason, it will be rescheduled for execution in the next time slice. If the task runs at 13:30 and fails with some unhandled exception, then TaskService will run the task twice at 14:00. It will first run the task for the 13:30 time slice and then for the 14:00 time slice.

Parameters:

time - The starting time from which the initial execution is scheduled. The scheduled execution time depends on Task.getInterval(). Tasks are scheduled to execute on fixed time boundaries. For example, if the task has an interval of 15 minutes, then it will get scheduled to run at 14:00, 14:15, 14:30, 14:45, 15:00, and so on.

task - The task to schedule for execution

Returns:

The task with its scheduled execution time set