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Using the Scheduler

The Velocity scheduler lets you decide when and how your plugin tasks run, allowing fine control over execution. On Velocity, there is no main thread. All tasks run using the Velocity scheduler are thus run asynchronously.

Running a delayed task​

All scheduling works by using a TaskBuilder returned from the Scheduler. This fluent builder may be chained to configure the details of the scheduling.

server.getScheduler()
  .buildTask(plugin, () -> {
    // do stuff here
  })
  .delay(2L, TimeUnit.SECONDS)
  .schedule();

Here, we are scheduling a task to run 2 seconds later. Velocity requires the instance of your plugin, plugin above. If you are scheduling a task from your main plugin class you may simply use this.

Time arguments are specified as a long with a TimeUnit. Using time units makes scheduling delayed tasks more readable and allows for greater precision. 2L, TimeUnit.SECONDS is far easier to understand than the ambiguous 2000L.

You can also use a Duration to specify the time arguments, e.g.: Duration.ofSeconds(5L).

Running a repeating task​

Creating a repeating task is similar to a delayed task, but you must also specify repeat(long, TimeUnit). This example will repeat every 5 minutes.

server.getScheduler()
  .buildTask(plugin, () -> {
    // do stuff here
  })
  .repeat(5L, TimeUnit.MINUTES)
  .schedule();

Running a task now​

Tasks use the scheduler's cached thread pool for all execution, which reuses threads. To take advantage of this thread pool for running async tasks which run now, simply omit calling the delay and repeat methods of the TaskBuilder.

Cancellation​

The schedule() method returns a ScheduledTask, which may then be used to cancel the task involved via the cancel() method. Tasks cannot be uncancelled.

Additionally, task.status() returns the current status of the task.

ScheduledTask task = server.getScheduler()
  .buildTask(plugin, () -> {
    // do stuff here
  })
  .repeat(5L, TimeUnit.MINUTES)
  .schedule();
// ...
task.cancel();
// ...
System.out.println(task.status());

You can also schedule self-cancelling tasks using a Consumer<ScheduledTask>.

AtomicInteger integer = new AtomicInteger(0);

ScheduledTask task = server.getScheduler()
  .buildTask(plugin, (selfTask) -> {
    // do stuff here, for example...
    if (integer.addAndGet(1) > 10) {
      selfTask.cancel();
    }
  })
  .repeat(Duration.ofSeconds(4L))
  .schedule();

Obtaining tasks from a plugin​

You can get all tasks scheduled by a plugin with tasksByPlugin(Object).

Collection<ScheduledTask> tasks = server.getScheduler().tasksByPlugin(plugin);
// then you can control them, for example, cancel all task scheduled by a plugin
for (ScheduledTask task : tasks) {
  task.cancel();
}
Written for version: 1.21