/// <summary>
/// Execute a command batch and synchronizes the client data model with the newer records from the server.
/// </summary>
public static void Execute(Batch batch)
{
// This 'try' block will insure that the mutual exclusion locks are released.
try
{
// Make sure only one thread at a time tries to refresh the data model.
ClientMarketData.clientDataMutex.WaitOne();
// Switching credentials without exiting the application will force the data model to be cleared and the row
// counting to begin at zero again. That is, it effectively resets the client data model.
if (ClientMarketData.isReset)
{
ClientMarketData.isReset = false;
ClientMarketData.rowVersion = 0;
ClientMarketData.Clear();
}
// IMPORTANT CONCEPT: The rowVersion keeps track of the state of the client in-memory database. The server
// returns a value for us to use on the next cycle.
long rowVersion = ClientMarketData.rowVersion;
// IMPORTANT CONCEPT: Executing the 'GetClientMarketData' with a rowVersion returns to the client a DataSet
// with only records that are the same age or younger than the rowVersion. This reduces the traffic on the
// network to include only the essential records. We are also merging it with the current ClientMarketData,
// which adds new records and records that were deleted by the server.
AssemblyPlan assembly = batch.Assemblies.Add("Server Market Data");
TypePlan type = assembly.Types.Add("MarkThree.Guardian.Server.ServerMarketData");
TransactionPlan transaction = batch.Transactions.Add();
MethodPlan method = transaction.Methods.Add(type, "Reconcile");
Parameter rowVersionParameter = method.Parameters.Add(new InputParameter("rowVersion", rowVersion));
// Execute the the command to get the incremental changes from the server.
WebTransactionProtocol.Execute(batch);
// This is the updated data model information returned from the server.
ArrayList reconciledData = (ArrayList)method.Parameters.Return.Value;
// Optimization: Don't merge the results if there's nothing to merge.
if (reconciledData != null)
{
// IMPORTANT CONCEPT: Since the results will still be on the server if the client misses a refresh
// cycle, we take the attitude that thBzis update process doesn't have to wait for locks. That is, if we
// can't get all the tables locked quickly, we'll just wait until the next refresh period to get the
// results. This effectively prevents deadlocking on the client. Make sure all the tables are locked
// before populating them.
foreach (TableLock tableLock in ClientMarketData.TableLocks)
{
tableLock.AcquireWriterLock(ClientTimeout.LockWait);
}
// IMPORTANT CONCEPT: This broadcast can be used to set up conditions for the data event handlers. Often,
// optimizing algorithms will be used to consolidate the results of a merge. This will allow the event
// driven logic to clear previous results and set up initial states for handling the bulk update of data.
ClientMarketData.OnBeginMerge(typeof(ClientMarketData));
// IMPORANT CONCEPT: Once all the write locks have been obtained, we can merge the results. This will
// trigger the events associated with the tables for updated and deleted rows. Note that this 'Merge'
// method has different characteristics than the original one provided by Microsoft (that is, this one
// works).
ClientMarketData.rowVersion = MarketData.Merge(reconciledData);
// IMPORTANT CONCEPT: When the merge is complete, this will broadcast an event which allows optimization code
// to consolidate the results, examine the changed values and update reports based on the changed data.
ClientMarketData.OnEndMerge(typeof(ClientMarketData));
}
}
finally
{
// No matter what happens above, we need to release the locks acquired above.
foreach (TableLock tableLock in ClientMarketData.TableLocks)
{
if (tableLock.IsWriterLockHeld)
{
tableLock.ReleaseWriterLock();
}
}
// Other threads can now request a refresh of the data model.
ClientMarketData.clientDataMutex.ReleaseMutex();
}
// Throw a specialized exception if the server returned any errors in the Batch structure.
if (batch.HasExceptions)
{
throw new BatchException(batch);
}
}
