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Adhoc tasks

Adhoc tasks are typically used when you need to queue something to run in the background either immediately, where they would be executed as soon as possible, or as a one-off task at some future point in time.

Each adhoc task can be called multiple times, with each having its own custom data, and the ability to run as a different user.

Adhoc tasks are great for situations such as:

  • perform a pre-configured backup
  • migrate large quantities of data between different formats
  • send forum posts as an e-mail

Creating adhoc tasks​

To create a new adhoc task you should:

  1. create a new class which extends the \core\task\adhoc_task class;
  2. queue the task

Task class​

The class for your adhoc task, which extends the \core\task\adhoc_task class, should be in the classes/task directory of your plugin.

View example adhoc task
namespace mod_example\task;

/**
 * An example of an adhoc task.
 */
class do_something extends \core\task\adhoc_task {

    /**
     * Execute the task.
     */
    public function execute() {
        // Call your own api
    }
}

Custom data​

Adhoc tasks can be configured with custom data which is available when the task is run. You might think of custom data as method parameters.

The custom data fields can contain any JSON-serializable content, and can be set using the set_custom_data(mixed $content) method.

It can be fetched using the get_custom_data(): mixed method.

We recommend only ever calling set_custom_data() from within a factory method in the task class itself.

class do_something extends \core\task\adhoc_task {

    public static function instance(
        int $id,
        string $status,
    ): self {
        $task = new self();
        $task->set_custom_data((object) [
            'id' => $id,
            'status' => $status,
        ]);

        return $task;
    }

    public function execute() {
        $data = $this->get_custom_data();
        mtrace($data->id);
        mtrace($data->status);
    }
}

Task features​

Adhoc tasks include a number of useful features which are important to be aware of.

Running as a specific user​

Unless otherwise specified, all tasks will run as the CLI admin user. This is often undesirable and, where relevant, you should specify a userid to run the task as.

// Run this task as a specific user:
$task->set_userid($someuser->id);
note

We recommend that setting of the task user should also be performed within a factory method.

Set a task to run at a future time​

You may need to plan to run a task at a future time - for example you may queue a forum digest task to run at a particular time. This can be accomplished using the set_next_run_time() function before queueing the task, for example:

$task->set_next_run_time($futuretime);
\core\task\manager::queue_adhoc_task($task);
note

The set_next_run_time() function takes a unix time stamp. Tasks are not guaranteed to run at a specific time, but they will not be run before that time.

Ignore duplicate adhoc tasks​

In some situations you may only wish to queue an adhoc task if an identical adhoc task does not already exist. This can be useful in situations where you are adding a set of items to a bucket for later processing and only wish to process all items once.

When requested, the queue_adhoc_task() function will ignore any task where all of the following match an existing task in the queue:

  • classname - the class defining the task to be processed
  • component - the component that the task belongs
  • customdata - any custom data for this instance
  • userid - the user that the task will be run as

Duplicate adhoc task detection can be enabled by passing a truthy value as the second argument to queue_adhoc_task(), for example:

\core\task\manager::queue_adhoc_task($task, true);
Custom data

If creating tasks which will contain a subset of data which will also be run by another instance of the same task type, you should put the data into a database table rather than the task custom data.

Rescheduling an adhoc task​

Similar to ignoring duplicate adhoc tasks there are situations which require you re_schedule_ a matching task instead. This may happen, for example, in a situation where there is too much churn of your source data.

The reschedule_or_queue_adhoc_task() function will locate any existing task matching the following fields, and update its time with the time from the new entry:

  • classname - the class defining the task to be processed
  • component - the component that the task belongs
  • customdata - any custom data for this instance
  • userid - the user that the task will be run as
\core\task\manager::reschedule_or_queue_adhoc_task($task);

Retrying failing tasks​

Since 4.4

The number of retries for a failing task can be controlled using the set_attempts_available() method on the task before it is queued. If not specified a task will be allowed 12 retries.

$task->set_attempts_available(2);
\core\task\manager::queue_adhoc_task($task);

You can get the remaining available attempts of a task by calling the get_attempts_available() function.

$task->get_attempts_available();

Tasks are retried by default, but this behaviour can be modified by overriding the retry_until_success() method in your task class, for example:

public function retry_until_success(): bool {
    return false;
}