/// <summary>
/// Dequeue a WorkItem for processing
/// </summary>
/// <returns>A WorkItem or null if the queue has stopped</returns>
public WorkItem Dequeue()
{
SpinWait sw = new SpinWait();
do
{
WorkItemQueueState cachedState = State;
if (cachedState == WorkItemQueueState.Stopped)
{
return(null); // Tell worker to terminate
}
int cachedRemoveId = _removeId;
int cachedAddId = _addId;
// Empty case (or paused)
if (cachedRemoveId == cachedAddId || cachedState == WorkItemQueueState.Paused)
{
// Spin a few times to see if something changes
if (sw.Count <= spinCount)
{
sw.SpinOnce();
}
else
{
// Reset to wait for an enqueue
_mreAdd.Reset();
// Recheck for an enqueue to avoid a Wait
if ((cachedRemoveId != _removeId || cachedAddId != _addId) && cachedState != WorkItemQueueState.Paused)
{
// Queue is not empty, set the event
_mreAdd.Set();
continue;
}
// Wait for something to happen
_mreAdd.Wait(500);
}
continue;
}
// Validate that we are the current dequeuer
if (Interlocked.CompareExchange(ref _removeId, cachedRemoveId + 1, cachedRemoveId) != cachedRemoveId)
{
continue;
}
// Dequeue our work item
WorkItem work;
while (!_innerQueue.TryDequeue(out work))
{
}
;
// Add to items processed using CAS
Interlocked.Increment(ref _itemsProcessed);
return(work);
} while (true);
}
/// <summary>
/// Removes the first element from the queue and returns it (or <c>null</c>).
/// </summary>
/// <param name="blockWhenEmpty">
/// If <c>true</c> and the queue is empty, the calling thread is blocked until
/// either an element is enqueued, or <see cref="Stop"/> is called.
/// </param>
/// <returns>
/// <list type="bullet">
/// <item>
/// <term>If the queue not empty</term>
/// <description>the first element.</description>
/// </item>
/// <item>
/// <term>otherwise, if <paramref name="blockWhenEmpty"/>==<c>false</c>
/// or <see cref="Stop"/> has been called</term>
/// <description><c>null</c>.</description>
/// </item>
/// </list>
/// </returns>
public Event Dequeue(bool blockWhenEmpty)
{
SpinWait sw = new SpinWait();
do
{
int cachedRemoveId = _removeId;
int cachedAddId = _addId;
// Empty case
if (cachedRemoveId == cachedAddId)
{
if (!blockWhenEmpty || _stopped != 0)
{
return(null);
}
// Spin a few times to see if something changes
if (sw.Count <= spinCount)
{
sw.SpinOnce();
}
else
{
// Reset to wait for an enqueue
_mreAdd.Reset();
// Recheck for an enqueue to avoid a Wait
if (cachedRemoveId != _removeId || cachedAddId != _addId)
{
// Queue is not empty, set the event
_mreAdd.Set();
continue;
}
// Wait for something to happen
_mreAdd.Wait(500);
}
continue;
}
// Validate that we are the current dequeuer
if (Interlocked.CompareExchange(ref _removeId, cachedRemoveId + 1, cachedRemoveId) != cachedRemoveId)
{
continue;
}
// Dequeue our work item
Event e;
while (!_queue.TryDequeue(out e))
{
if (!blockWhenEmpty || _stopped != 0)
{
return(null);
}
}
return(e);
} while (true);
}
