// NB: Async void should be avoided; it should only be used for event handlers.Timer.Elapsed is an event handler.So, it's not necessarily wrong here.
// c.f. http://stackoverflow.com/questions/25007670/using-async-await-inside-the-timer-elapsed-event-handler-within-a-windows-servic
private async void DoWorkAsync(object group)
{
// DoWork needs to be re-entrant as Timer may call the callback before the previous callback has returned.
// So, because a task may take longer than the period itself, DoWork needs to check if it's still running.
ShellContext shellContext = _orchardHost.GetOrCreateShellContext(_shellSettings);
var groupName = group as string ?? "";
foreach (var task in _tasks[groupName])
{
var taskName = task.GetType().FullName;
using (var scope = shellContext.EnterServiceScope())
{
try
{
if (_states[task] != BackgroundTaskState.Idle)
{
return;
}
lock (_states)
{
// Ensure Terminate() was not called before
if (_states[task] != BackgroundTaskState.Idle)
{
return;
}
_states[task] = BackgroundTaskState.Running;
}
if (Logger.IsEnabled(LogLevel.Information))
{
Logger.LogInformation("Start processing background task \"{0}\".", taskName);
}
await task.DoWorkAsync(scope.ServiceProvider, _applicationLifetime.ApplicationStopping);
if (Logger.IsEnabled(LogLevel.Information))
{
Logger.LogInformation("Finished processing background task \"{0}\".", taskName);
}
}
catch (Exception ex)
{
if (Logger.IsEnabled(LogLevel.Error))
{
Logger.LogError(ex, $"Error while processing background task \"{taskName}\"");
}
}
finally
{
lock (_states)
{
// Ensure Terminate() was not called during the task
if (_states[task] != BackgroundTaskState.Stopped)
{
_states[task] = BackgroundTaskState.Idle;
}
}
}
}
}
}
