/// <summary>
/// Removes and returns an item from one of the specified collections in an asynchronous manner.
/// </summary>
public static Task <AnyResult <T> > TakeFromAnyAsync(AsyncCollection <T>[] collections, CancellationToken cancellationToken)
{
if (collections == null)
{
throw new ArgumentNullException("collections");
}
if (collections.Length <= 0 || collections.Length > TakeFromAnyMaxCollections)
{
throw new ArgumentException(String.Format("The collection array can't contain less than 1 or more than {0} collections.", TakeFromAnyMaxCollections), "collections");
}
if (cancellationToken.IsCancellationRequested)
{
return(CanceledTask <AnyResult <T> > .Value);
}
ExclusiveCompletionSourceGroup <T> exclusiveSources = new ExclusiveCompletionSourceGroup <T>();
// Fast route: we attempt to take from the top-priority queues that have any items.
// If the fast route succeeds, we avoid allocating and queueing a bunch of awaiters.
for (int i = 0; i < collections.Length; i++)
{
if (collections[i].Count > 0)
{
AnyResult <T>?result = TryTakeFast(exclusiveSources, collections[i], i);
if (result.HasValue)
{
return(Task.FromResult(result.Value));
}
}
}
// No luck during the fast route; just queue the rest of awaiters.
for (int i = 0; i < collections.Length; i++)
{
AnyResult <T>?result = TryTakeFast(exclusiveSources, collections[i], i);
if (result.HasValue)
{
return(Task.FromResult(result.Value));
}
}
// None of the collections had any items. The order doesn't matter anymore, it's time to start the competition.
exclusiveSources.UnlockCompetition(cancellationToken);
return(exclusiveSources.Task);
}
private static AnyResult <T>?TryTakeFast(ExclusiveCompletionSourceGroup <T> exclusiveSources, AsyncCollection <T> collection, int index)
{
// This can happen if the awaiter has already been created during the fast route.
if (exclusiveSources.IsAwaiterCreated(index))
{
return(null);
}
Task <T> collectionTask = collection.TakeAsync(exclusiveSources.CreateAwaiterFactory(index));
// One of the collections already had an item and returned it directly
if (collectionTask != null && collectionTask.IsCompleted)
{
exclusiveSources.MarkAsResolved();
return(new AnyResult <T>(collectionTask.Result, index));
}
else
{
return(null);
}
}
