Services is one of those Microsoft products whose identity is murky at best.
Like SharePoint Services, InfoPath
and other Microsoft software that doesn’t seem entirely focused on a single
mission, Enterprise Services tends to get lost in the crowd. Whispers that it
is nothing more than warmed-over COM+ don’t help. And the serious lack of useful
documentation almost serves to give it a reputation as something to avoid.
other hand, if you’re stuck in client-server space and don’t have the budget
for the heavy-duty stuff, Enterprise Services can equip you to take the
enterprise plunge. Here are some powerful features and tricks that aren’t
particularly visible to the naked eye.
1. Abstract the layers of your architecture with loosely-coupled events
Enterprise Services inherits a substantial legacy from
COM+, including the ability of serviced components to publish events to the
COM+ facility. COM+ takes over the task of connecting events to clients, and a
layer of abstraction is born.
events (LCEs) in Enterprise Services are key building
blocks in your multi-tiered environment. Traffic between server(s) and
client(s)—that is, published events that clients invoke—is driven by event
classes registered with COM+; classes that deliver events to subscribing
clients. Connections don’t need to be managed from the data source, so your
data layer is decoupled; events and clients are dynamically coupled, so you
have true enterprise connectivity through your application environment.
2. Optimize your applications, using Enterprise Services concurrency and
Services synchronization advances the synchronization techniques of COM+,
taking you from apartments to activities: synchronization domains that are
based on logical threads,
rather than physical threads. Physical threads instead form chains that
comprise a logical thread, called causalities.
domains inherit the TNA (thread-neutral apartment) from COM+; activities
leverage the TNA feature of leaving a thread that has entered via a method call
even after the method call is done, eliminating a thread switch. Overhead is
trimmed because nothing changes but a few TNA variables. If your applications
use synchronization domain activities heavily, the overhead savings will be
considerable and the environmental performance more optimal.
3. Isolation levels can be configured, allowing you to fine-tune system
data integrity across transactions is a matter of locking data while it is
being used. There are a lot of variables involved in how well this practice
works, including the length of time the data is locked, how many users need it,
how often it changes, and so on.
This can be
controlled through Isolation level. If you’re running Enterprise Services on Windows Server 2003, you have control of the Isolation
level applied to the locking of data through the Isolation property of the
transaction attribute. High isolation levels mean higher data integrity but
less concurrency; lower isolation levels increase concurrency but also increase
risk to data integrity. The best of all worlds is to find a balance that is
right for the application.
4. Manage application states
Services enables you to maintain object states in a number of different places,
and your design choices in this area can affect your application scalability.
Why? Because tracking object state across multiple client calls to an object
and then across many objects, can add up to a very significant consumption of
Enterprise Services, you can manage state at the serviced component level or
the client application level, by storing state values at that level. How do you
choose which level is appropriate? There are many factors: how fast must state
be accessed? How often does it change? Is it linked to users, an application, or
multiple applications? Are components load-balanced? Is the object
transactional? The point is, Enterprise Services
allows you to choose.
also, if it makes sense, store state values in a database—useful if, for
instance, the state of an application must be restored if your system goes down—or
in shared properties (through the Shared Property Manager).
5. Leverage Enterprise Services concurrency and synchronization to enhance
quality of data access
thread concept put forth in #2 offers other across-the-board advantages, not
the least of which is an overall reduction in lock-out issues—so data issues
due to access errors can be dramatically trimmed. Logical threads muster
processes into activities, and those processes are actually facilitated by
different physical threads. However, since activities themselves are
cross-context, cross-process, cross-application, and traffic would get worse,
not better, if the traditional approach of locking threads was used. Instead,
locks are not used on threads, but activities.
an activity assumes a single logical thread, though the synchronization domain
itself can encompass many applications, many contexts, many processes, many
physical threads—you really can get very creative with it. The restriction of
the single logical thread permits you to link the whole thing together and lock
it up with a single event, rather than many. If an activity has a lock on a
particular object within the domain, then any other activity wanting access to
it waits until the causality lock—the lock on the logical thread—is released.
One lock, not many, per activity. Object state is therefore no longer a
programming concern per se; activities are availed of synchronization objects
that a thread locks upon entering. Those synchronization objects are unlocked,
and the activity made available to a new logical thread, when the causality
lock is released.
6. Reduce code and development time of applications by aliasing components
running Enterprise Services on Windows Server 2003, there’s a neat trick you
can do in development that will yield a faster, smaller app: you can alias
components, configuring a single physical component implementation lots of
you might develop a component and use it many times, in different instances—only
register and configure it once—so to get multiple uses out of it, you must
create multiple versions, each with its own constructor. The result is lots of
cutting and pasting of code.
Enterprise Services (on Server 2003), it’s much simpler. Since you don’t have
to re-implement the component, you’re cutting down on code; you’re essentially
recycling the component implementation, and you’re doing it at the binary
level, which is faster, cheaper, and better.
7. Distribute and manage components over a network
COM+ legacy that Enterprise Services leverages is .NET Remoting, which allows
events to be sent across your network: “Delegates” are created and events
that established parameters and handler method return type for a client. The
handler method is implemented and registered with the object event, so the
object can remain tied to the client through the event.
distribute LCEs (see #1) across multiple systems in a
couple of different ways.
is subscriber-side networking. Subscribers are defined for both the client
system and the system handling the LCE traffic, and COM+ routing is used to do
event distribution. (As you might guess, this technique can only be used with persistent
proxies are another way. You can create a proxy that connects to an event
class, since event classes are serviced components. This allows you to network
between event classes and publishers.
also make the publisher-to-subscriber call asynchronous, passing messages to
message queues, with serviced component methods invoked via those messages to
buffer the system and further decouple components. This technique can be
applied with LCEs and event classes.
8. Create services without components
serviced component is the star of the Enterprise Services show. The idea is one
of those we-enforce-good-design ideas that Microsoft foists upon unsuspecting
developers: COM+ is the lightning in the distributed applications bottle, and
to leverage COM+, your code has to be registered with component services, via a
ServicedComponent class—so that your classes are
parsed by service.
running Enterprise Services on Windows 2003, however, life is simpler. Services
are applied to a component as a matter of course in a service domain; it is a
de facto serviced component, without actually inheriting anything from ServicedComponent.
9. Manage transactions through attributes
One of the
major reasons to use Enterprise Services is the automation of transactions, to
get away from having to manage transactions in code. Enterprise Services allows
you to go in a more efficient direction, managing transactions in attributes.
manage transactions in code, you create method arguments that pass
transactions. In Enterprise Services, you can have transactions generated by
the runtime, and control an object in a class with respect to transactions that
apply. The Transaction attribute is applied to classes implementing serviced
components, and allows you to context with respect to a transaction, which
components participate in a transaction, when a new transaction is created, and
10. Object-bound components are assumed
context is used to (among other things) control components with respect to
threading and accessibility. Enterprise Services facilitates the creation of
context-bound components by virtue of their base class (ServicedComponent) deriving from the class System.ContextBoundObject. You have .NET Remoting
context as a matter of course with serviced components. Context simplifies the
fine-tuning of components to the process they support, by defining their
runtime requirements and compatibilities.