private TaskResult ReadQueue(LazyQueue <TVal> queue)
{
var result = new TaskResult {
Queue = queue
};
TVal current;
if (_ignoreFailures)
{
try
{
result.HasValue = queue.TryPeek(out current);
}
catch (Exception ex)
{
LogWarning(ex);
current = default(TVal);
}
}
else
{
result.HasValue = queue.TryPeek(out current);
}
result.Value = current;
return(result);
}
private IEnumerable <T> GetAggregateEnumerable()
{
// Used to pick the right element from each sub query in the right order
var comparer = new OrderingComparer <T>(Expression);
// Create lazy queues over each sub query so we can lazily pull items from it
var lazyQueues = _subQueries.Select(query => new LazyQueue <T>(query.GetEnumerator())).ToList();
// Used to keep track of everything we've seen so far (we never show duplicates)
var seen = new HashSet <T>(_equalityComparer);
do
{
T minElement = default(T);
LazyQueue <T> minQueue = null;
// Run tasks in parallel
var tasks = (from queue in lazyQueues
select Task.Factory.StartNew(() => {
T current;
return(new {
Empty = !queue.TryPeek(out current),
Value = current,
Queue = queue,
});
})).ToArray();
// Wait for everything to complete
Task.WaitAll(tasks);
foreach (var task in tasks)
{
if (!task.Result.Empty)
{
// Keep track of the minimum element in the list
if (minElement == null || comparer.Compare(task.Result.Value, minElement) < 0)
{
minElement = task.Result.Value;
minQueue = task.Result.Queue;
}
}
else
{
// Remove the enumerator if it's empty
lazyQueues.Remove(task.Result.Queue);
}
}
if (lazyQueues.Any())
{
if (seen.Add(minElement))
{
yield return(minElement);
}
// Clear the top of the enumerator we just peeked
minQueue.Dequeue();
}
} while (lazyQueues.Any());
}
/// <summary>
/// Reads the minimal set of queries
/// </summary>
/// <param name="comparer"></param>
/// <returns></returns>
private IEnumerable <TVal> ReadOrderedQueues(IComparer <TVal> comparer)
{
// Create lazy queues over each sub query so we can lazily pull items from it
var lazyQueues = _subQueries.Select(query => new LazyQueue <TVal>(query.GetEnumerator())).ToList();
// Used to keep track of everything we've seen so far (we never show duplicates)
var seen = new HashSet <TVal>(_equalityComparer);
do
{
TVal minElement = default(TVal);
LazyQueue <TVal> minQueue = null;
// Run tasks in parallel
var tasks = (from queue in lazyQueues
select Task.Factory.StartNew <TaskResult>(() => ReadQueue(queue))
).ToArray();
// Wait for everything to complete
Task.WaitAll(tasks);
foreach (var task in tasks)
{
if (task.Result.HasValue)
{
// Keep track of the minimum element in the list
if (minElement == null || comparer.Compare(task.Result.Value, minElement) < 0)
{
minElement = task.Result.Value;
minQueue = task.Result.Queue;
}
}
else
{
// Remove the enumerator if it's empty
lazyQueues.Remove(task.Result.Queue);
}
}
if (lazyQueues.Any())
{
if (seen.Add(minElement))
{
yield return(minElement);
}
// Clear the top of the enumerator we just peeked
minQueue.Dequeue();
}
} while (lazyQueues.Count > 0);
}