/// <summary>
/// Starts a multi-threaded queue listener that uses the specified number of dequeue threads.
/// </summary>
/// <param name="threadCount">The number of dequeue threads.</param>
public void StartListener(int threadCount)
{
Guard.ArgumentNotZeroOrNegativeValue(threadCount, "threadCount");
var callToken = TraceManager.WorkerRoleComponent.TraceIn(this.queueLocation.StorageAccount, this.queueLocation.QueueName, threadCount);
try
{
// The collection of dequeue tasks needs to be reset on each call to this method.
if (this.dequeueTasks.IsAddingCompleted)
{
this.dequeueTasks = new BlockingCollection <Task>(this.dequeueTaskList);
}
for (int i = 0; i < threadCount; i++)
{
CancellationToken cancellationToken = this.cancellationSignal.Token;
CloudQueueListenerDequeueTaskState <T> workerState = new CloudQueueListenerDequeueTaskState <T>(Subscriptions, cancellationToken, this.queueLocation, this.queueStorage);
// Start a new dequeue task and register it in the collection of tasks internally managed by this component.
this.dequeueTasks.Add(Task.Factory.StartNew(DequeueTaskMain, workerState, cancellationToken, TaskCreationOptions.LongRunning, TaskScheduler.Default));
}
// Mark this collection as not accepting any more additions.
this.dequeueTasks.CompleteAdding();
}
finally
{
TraceManager.WorkerRoleComponent.TraceOut(callToken);
}
}
/// <summary>
/// Implements a task performing dequeue operations against a given Windows Azure queue.
/// </summary>
/// <param name="state">An object containing data to be used by the task.</param>
private void DequeueTaskMain(object state)
{
CloudQueueListenerDequeueTaskState <T> workerState = (CloudQueueListenerDequeueTaskState <T>)state;
var callToken = TraceManager.WorkerRoleComponent.TraceIn(workerState.QueueLocation.StorageAccount, workerState.QueueLocation.QueueName);
int idleStateCount = 0;
TimeSpan sleepInterval = DequeueInterval;
try
{
// Run a dequeue task until asked to terminate or until a break condition is encountered.
while (workerState.CanRun)
{
try
{
var queueMessages = from msg in workerState.QueueStorage.Get <T>(workerState.QueueLocation.QueueName, DequeueBatchSize, workerState.QueueLocation.VisibilityTimeout).AsParallel() where msg != null select msg;
int messageCount = 0;
// Check whether or not work items arrived to a queue while the listener was idle.
if (idleStateCount > 0 && queueMessages.Count() > 0)
{
if (QueueWorkDetected != null)
{
QueueWorkDetected(this);
}
}
// Process the dequeued messages concurrently by taking advantage of the above PLINQ query.
queueMessages.ForAll((message) =>
{
// Reset the count of idle iterations.
idleStateCount = 0;
// Notify all subscribers that a new message requires processing.
workerState.OnNext(message);
// Once successful, remove the processed message from the queue.
workerState.QueueStorage.Delete <T>(message);
// Increment the number of processed messages.
messageCount++;
});
// Check whether or not we have done any work during this iteration.
if (0 == messageCount)
{
// Increment the number of iterations when we were not doing any work (e.g. no messages were dequeued).
idleStateCount++;
// Call the user-defined delegate informing that no more work is available.
if (QueueEmpty != null)
{
// Check if the user-defined delegate has requested a halt to any further work processing.
if (QueueEmpty(this, idleStateCount, out sleepInterval))
{
TraceManager.WorkerRoleComponent.TraceInfo(String.Format(CultureInfo.CurrentCulture, TraceLogMessages.CloudQueueListenerTerminatedWithNoMoreWork, this.queueLocation.QueueName, this.queueLocation.StorageAccount));
// Terminate the dequeue loop if user-defined delegate advised us to do so.
break;
}
}
// Enter the idle state for the defined interval.
Thread.Sleep(sleepInterval);
}
}
catch (Exception ex)
{
if (ex is OperationCanceledException)
{
throw;
}
else
{
// Offload the responsibility for handling or reporting the error to the external object.
workerState.OnError(ex);
// Sleep for the specified interval to avoid a flood of errors.
Thread.Sleep(sleepInterval);
}
}
}
}
finally
{
workerState.OnCompleted();
TraceManager.WorkerRoleComponent.TraceOut(callToken, workerState.QueueLocation.StorageAccount, workerState.QueueLocation.QueueName);
}
}
