1	COM+ Services
2	COM – Review Package functionality in binary code units Operating System provides a simple framework for objects to interact
3	COM – Review Operating system does not provide any functionality for complex interaction of the objects
4	COM+ There are many infrastructure facilities created for many enterprise applications These services are now provided by the Operating System
5	COM+ Features Neutral Apartments Transactions (formerly MTS) Queued Components COM+ Events Load Balancing
6	Apartments Apartments are conceptual spaces in the operating system where the OS places COM objects In Windows NT 4.0 there were two apartments STA (Single Threaded Apartment) MTA (Multi Threaded Apartment)
7	STA Many per process Only one thread allowed access to the apartment Safe Crossing apartment boundary costs a lot
8	MTA One per process Not safe, but very fast More difficult to program
9	Problems If an object in an STA calls an object in an MTA there is a substantial performance hit.
10	Neutral Apartment Allows any thread to enter Only one thread allowed in at a time COM+ provides synchronization
11	Transactions COM+ Transactions are successor to MTS We’re going to assume that audience knows MTS
12	Improvements to MTS Object Pooling now a reality
13	Object Pooling When an object is done with whatever it is doing, it alerts COM+ by calling SetComplete COM+ then calls Deactivate, but does not destroy the object COM+ removes the object from the client (invisibly) and puts it in a pool to be used by other clients When another object is requested, the object is retrieved from the pool, Activate is called and it is handed to the client
14
15	PooledObject IPooledObject Multiply(int Op1, int Op2) IObjectControl Activate Deactivate CanBePooled
16	Client Dim oPooledObject As PooledObject Dim Result As Integer Set oPooledObject = CreateObject("PooledObjectLib.PooledObject) Result = oPooledObject.Multiply(5, 6)
17	Queued Components Allows clients to call methods on a COM object when the COM object is not available.
18
19	Details Configure COM+ Application in Component Services Manager as Queued Configure interface as Queued Create object with a moniker – huh? Like this – CreateObject(“queue:/new:ProgId”) Calls are then coded and stored in a Message Queue
20	Drawbacks No out arguments No App specific error codes (HRESULT’s) All arguments must be passed ByVal Some mechanism to report failures must be implemented if necessary
21	Events A component fires an event Another component hears the event and performs some action Currently, for another component to act on the event, the first component must be altered
22	COM+ Events The event is defined within the operating system, not the component Any component can be written to respond to the event Any client can instantiate the event class and fire the event
23
24	Load Balancing Shares COM calls between objects on multiple servers Available only in Windows 2K AppCenter
25	Load Balancing
26	Summary Lots of functionality becomes administrative instead of programmatic COM+ moves functionality previously requiring extensive infrastructure into the Operating System