public static async Task <T> Receive <T>(SqlConnection conn, string channelName, CancellationToken ct, params Type[] otherTypes)
{
using (var cmd = conn.CreateCommand())
{
cmd.CommandTimeout = 0;
cmd.CommandType = System.Data.CommandType.StoredProcedure;
cmd.CommandText = "[SSBMB]." + channelName + "_Receive";
using (var reader = await cmd.ExecuteReaderAsync(ct))
{
if (!ct.IsCancellationRequested && await reader.ReadAsync(ct))
{
return(SSBSerializationHelpers.Deserialize <T>((string)reader["MessageBody"], otherTypes));
}
else
{
return(default(T));
}
}
}
}
public static IEnumerable <T> Listen <T>(Func <SqlConnection> conn, string topicName, CancellationToken ct, params Type[] otherTypes)
{
string subscriptionName;
var currentConn = conn();
currentConn.Open();
using (var cmd = currentConn.CreateCommand())
{
cmd.CommandType = System.Data.CommandType.StoredProcedure;
cmd.CommandText = "[SSBMB].Subscribe";
cmd.Parameters.Add(new SqlParameter("@TopicName", topicName));
cmd.Parameters.Add(new SqlParameter("@SubscriptionName", DBNull.Value));
subscriptionName = (string)cmd.ExecuteScalar();
Trace.TraceInformation("New subscription created: {0}", subscriptionName);
}
// Repeatedly open a new connection and attempt to reconnect to the same subscription
while (!ct.IsCancellationRequested)
{
using (var cmd = currentConn.CreateCommand())
{
cmd.CommandTimeout = 0;
cmd.CommandType = System.Data.CommandType.StoredProcedure;
cmd.CommandText = "[SSBMB]." + subscriptionName + "_Listen";
var firstResultSet = true;
SqlDataReader reader;
try
{
reader = cmd.ExecuteReader();
}
catch (SqlException) // Assumes subscription is missing
{
currentConn.Close();
yield break;
// if the Subscription was cleaned up between reconnects, we
// must re-Subscribe with a new name and let the Subscriber know that
// we may have missed some messages, so they need to reset their caches
// which are based on this stream
}
using (reader)
{
while (!ct.IsCancellationRequested)
{
string messageBody;
T message = default(T);
bool abandon = false;
try
{
if (reader.Read() || (!firstResultSet && reader.NextResult() && reader.Read()))
{
messageBody = (string)reader["MessageBody"];
message = SSBSerializationHelpers.Deserialize <T>(messageBody, otherTypes);
}
else
{
continue;
}
}
catch (SqlException) // Assumes connection was terminated
{
currentConn.Close();
try
{
currentConn = conn(); // Attempt to reconnect on same subscription
currentConn.Open(); // takes effect on close
break; // resume listening
}
catch
{
currentConn.Close();
abandon = true;
}
}
catch // Something else went wrong, like Deserialization so abandon this subscription
{
currentConn.Close();
abandon = true;
}
finally
{
firstResultSet = false; // after the first result, clear this, no matter what
}
// can't put yield return in try catch or finally blocks, making the code a little awkward.
if (abandon)
{
yield break; // end the Enumeration
}
else
{
yield return(message);
}
try
{
if (!reader.NextResult()) // no more result sets?? this is not expected
{
throw new Exception("No next result set");
}
}
catch // Assumes connection was terminated
{
currentConn.Close();
try
{
currentConn = conn(); // Attempt to reconnect on same subscription
currentConn.Open();
break; // resume listening
}
catch
{
currentConn.Close();
abandon = true;
}
}
if (abandon)
{
yield break; // end the Enumeration
}
}
}
}
}
currentConn.Close();
}