I don't understand why, but there appears to be no mechanism in the client library for performing many queries in parallel for Windows Azure Table Storage. I've created a template class that can be used to save considerable time, and you're welcome to use it however you wish. I would appreciate however, if you could pick it apart, and provide feedback on how to improve this class.
public class AsyncDataQuery<T> where T: new()
{
public AsyncDataQuery(bool preserve_order)
{
m_preserve_order = preserve_order;
this.Queries = new List<CloudTableQuery<T>>(1000);
}
public void AddQuery(IQueryable<T> query)
{
var data_query = (DataServiceQuery<T>)query;
var uri = data_query.RequestUri; // required
this.Queries.Add(new CloudTableQuery<T>(data_query));
}
/// <summary>
/// Blocking but still optimized.
/// </summary>
public List<T> Execute()
{
this.BeginAsync();
return this.EndAsync();
}
public void BeginAsync()
{
if (m_preserve_order == true)
{
this.Items = new List<T>(Queries.Count);
for (var i = 0; i < Queries.Count; i++)
{
this.Items.Add(new T());
}
}
else
{
this.Items = new List<T>(Queries.Count * 2);
}
m_wait = new ManualResetEvent(false);
for (var i = 0; i < Queries.Count; i++)
{
var query = Queries[i];
query.BeginExecuteSegmented(callback, i);
}
}
public List<T> EndAsync()
{
m_wait.WaitOne();
return this.Items;
}
private List<T> Items { get; set; }
private List<CloudTableQuery<T>> Queries { get; set; }
private bool m_preserve_order;
private ManualResetEvent m_wait;
private int m_completed = 0;
private void callback(IAsyncResult ar)
{
int i = (int)ar.AsyncState;
CloudTableQuery<T> query = Queries[i];
var response = query.EndExecuteSegmented(ar);
if (m_preserve_order == true)
{ // preserve ordering only supports one result per query
this.Items[i] = response.Results.First();
}
else
{ // add any number of items
this.Items.AddRange(response.Results);
}
if (response.HasMoreResults == true)
{ // more data to pull
query.BeginExecuteSegmented(response.ContinuationToken, callback, i);
return;
}
m_completed = Interlocked.Increment(ref m_completed);
if (m_completed == Queries.Count)
{
m_wait.Set();
}
}
}
