/// <summary>
/// Implements a callback delegate which will be invoked whenever there is no more work available on the queue.
/// </summary>
/// <param name="sender">The source of the event.</param>
/// <param name="idleCount">The value indicating how many times the queue listener has been idle.</param>
/// <param name="delay">The time interval during which the queue listener will be instructed to sleep before performing next unit of work.</param>
/// <returns>A boolean flag indicating that the queue listener should stop processing any further work and must terminate.</returns>
private bool HandleQueueEmptyEvent(object sender, int idleCount, out TimeSpan delay)
{
// The sender is an instance of the ICloudQueueServiceWorkerRoleExtension, we can safely perform type casting.
ICloudQueueServiceWorkerRoleExtension queueService = sender as ICloudQueueServiceWorkerRoleExtension;
// Find out which extension is responsible for retrieving the worker role configuration settings.
IWorkItemProcessorConfigurationExtension config = Extensions.Find <IWorkItemProcessorConfigurationExtension>();
// Get the current state of the queue listener to determine point-in-time load characteristics.
CloudQueueListenerInfo queueServiceState = queueService.QueryState();
// Set up the initial parameters, read configuration settings.
int deltaBackoffMs = 100;
int minimumIdleIntervalMs = Convert.ToInt32(config.Settings.MinimumIdleInterval.TotalMilliseconds);
int maximumIdleIntervalMs = Convert.ToInt32(config.Settings.MaximumIdleInterval.TotalMilliseconds);
// Calculate a new sleep interval value that will follow a random exponential back-off curve.
int delta = (int)((Math.Pow(2.0, (double)idleCount) - 1.0) * (new Random()).Next((int)(deltaBackoffMs * 0.8), (int)(deltaBackoffMs * 1.2)));
int interval = Math.Min(minimumIdleIntervalMs + delta, maximumIdleIntervalMs);
// Pass the calculated interval to the dequeue task to enable it to enter into a sleep state for the specified duration.
delay = TimeSpan.FromMilliseconds((double)interval);
// As soon as interval reaches its maximum, tell the source dequeue task that it must gracefully terminate itself
// unless this is a last deqeueue task. If so, we are not going to keep it running and continue polling the queue.
return(delay.TotalMilliseconds >= maximumIdleIntervalMs);
}
/// <summary>
/// Implements a callback delegate to be invoked whenever a new work has arrived to a queue while the queue listener was idle.
/// </summary>
/// <param name="sender">The source of the event.</param>
private void HandleQueueWorkDetectedEvent(object sender)
{
// The sender is an instance of the ICloudQueueServiceWorkerRoleExtension, we can safely perform type casting.
ICloudQueueServiceWorkerRoleExtension queueService = sender as ICloudQueueServiceWorkerRoleExtension;
// Get the current state of the queue listener to determine point-in-time load characteristics.
CloudQueueListenerInfo queueServiceState = queueService.QueryState();
// Invoke a rule returning the number of queue tasks that would be required to handle the workload in a queue given its current depth.
int dequeueTaskCount = GetOptimalDequeueTaskCount(queueServiceState.CurrentQueueDepth);
// If the dequeue task count is less than computed above, start as many dequeue tasks as needed.
if (queueServiceState.ActiveDequeueTasks < dequeueTaskCount)
{
// Start the required number of dequeue tasks.
queueService.StartListener(dequeueTaskCount - queueServiceState.ActiveDequeueTasks);
}
}
