IMoBroScheduler

The IMoBroScheduler schedules one-off and recurring tasks, such as polling sensor values or fetching data from an external API.

Behavior

Keep the following in mind when scheduling tasks:

• Tasks run on background threads. Different tasks may run at the same time, so state shared between tasks must be thread-safe.
• A task never overlaps with itself. If an execution takes longer than its interval, the next execution is delayed until the current one has finished. A slow task therefore lowers the effective update rate instead of piling up. Cron tasks skip executions they missed while the previous one was still running.
• An unhandled exception stops the plugin. Any exception escaping a scheduled task is reported via IMoBroService.Error, which stops the plugin and sets its state to Error. Catch expected failures (e.g. a temporarily unavailable sensor or API) inside the task.
• Tasks are synchronous. All functions accept an Action. To call asynchronous code, block on it inside the task (see example).
• All tasks are removed when the plugin is re-created, e.g. after the user changes the plugin settings. Init() then runs again on the new instance, so tasks don't need to be re-scheduled manually. See Plugin Lifecycle.

Example: Failure-Tolerant Task

_scheduler.Interval(UpdateMetrics, TimeSpan.FromSeconds(2), TimeSpan.Zero);

private void UpdateMetrics()
{
  try
  {
    _mobro.UpdateMetricValue("cpu_usage", ReadCpuUsage());
  }
  catch (IOException e)
  {
    // a single failed read should not stop the plugin => log and try again on the next execution
    _logger.LogWarning(e, "Failed to read CPU usage");
  }
}

Calling Asynchronous Code

_scheduler.Interval(() => UpdateRatesAsync().GetAwaiter().GetResult(), TimeSpan.FromMinutes(5), TimeSpan.Zero);

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Functions

OneOff(Action, TimeSpan)

Schedules a task that is executed only once.

Parameters

Name	Type	Description
action	Action	The action to execute.
delay	TimeSpan	The delay before the execution.

Example

_scheduler.OneOff(LoadInitialData, TimeSpan.FromSeconds(2));

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Interval(Action, TimeSpan, TimeSpan)

Schedules a recurring task that is executed at a fixed interval.

Parameters

Name	Type	Description
action	Action	The action to execute.
interval	TimeSpan	The interval between executions.
delay	TimeSpan	The delay before the first execution.

Example

// first execution after 5 seconds, then every 2 seconds
_scheduler.Interval(UpdateMetrics, TimeSpan.FromSeconds(2), TimeSpan.FromSeconds(5));

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Cron(Action, string, TimeZoneInfo, TimeSpan)

Schedules a recurring task based on a cron expression.
The expression uses the Quartz format, which starts with a seconds field. See the Quartz cron documentation for details.

Parameters

Name	Type	Description
action	Action	The action to execute.
cron	string	The cron expression.
timeZone	TimeZoneInfo	The time zone the cron expression is evaluated in.
delay	TimeSpan	The delay before the cron schedule is activated.

Example

// every 15 minutes
_scheduler.Cron(UpdateExchangeRates, "0 0/15 * * * ?", TimeZoneInfo.Local, TimeSpan.Zero);

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Pause()

Temporarily pauses all scheduled tasks, e.g. while an external dependency is unavailable.

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Resume()

Resumes all previously paused tasks.

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Clear()

Removes all scheduled tasks. Executions that are currently running are not interrupted.

Example

// switch to a different polling interval
_scheduler.Clear();
_scheduler.Interval(UpdateMetrics, TimeSpan.FromSeconds(10), TimeSpan.Zero);