C# 4 and .NET 4

Tr a c in g ❘ 467
TraCing
With tracing, you can see messages from the running application. To get information about a running
application, you can start the application in the debugger. During debugging, you can walk through
the application step by step and set breakpoints at specifi c lines and when you reach specifi c conditions. The
problem with debugging is that a program with release code can behave differently from a program with
debug code. For example, while the program is stopping at a breakpoint, other threads of the application
are suspended as well. Also, with a release build, the compiler - generated output is optimized and, thus,
different effects can occur. There is a need to have information from a release build as well. Trace messages
are written with both debug and release code.
A scenario showing how tracing helps is described here. After an application is deployed, it runs on
one system without problems, while on another system intermediate problems occur. When you turn on
verbose tracing, the system with the problems gives you detailed information about what ’ s happening inside
the application. The system that is running without problems has tracing confi gured just for error messages
redirected to the Windows event log system. Critical errors are seen by the system administrator. The
overhead of tracing is very small, because you confi gure a trace level only when needed.
The tracing architecture has four major parts:
➤
➤
➤
➤
T h e source is the originator of the trace information. You use the source to send trace messages.
T h e switch defi nes the level of information to log. For example, you can request just error information
or detailed verbose information.
Tr a c e listeners defi ne where the trace
messages should be written to.
Listeners can have fi l t e r s attached. The
fi lt er de fi ne s wh at t rac e m e s s a ge s shou ld
be written by the listener. This way,
you can have different listeners for the
same source that write different levels of
information.
Figure 19 - 2 shows the major classes for tracing
and how they are connected, in a Visual
Studio class diagram. The TraceSource uses a
switch to defi ne what information to log. The
TraceSource has a TraceListenerCollection
associated with it, which trace messages
are forwarded to. The collection consists of
TraceListener objects, and every listener has a
TraceFilter connected.
figure 19-2
Several .NET technologies make use of trace sources that you just need to turn on
to see what’s going on. For example, WPF defines sources among others with the
names System.Windows.Data, System.Windows.RoutedEvent, System.Windows
.Markup, System.Windows.Media.Animation. However, with WPF, you need to turn
tracing on not only by confi guring listeners but also by setting within the registry key
HKEY_CURRENT_USER\Software\MicrosoftTracing\WPF a new DWORD to the name
ManagedTracing and the value 1.
Classes from the System.Net namespace use the trace source System.Net; WCF
uses the trace sources System.ServiceModel and System.ServiceModel.
MessageLogging. WCF tracing is discussed in Chapter 43, “Windows Communication
Foundation.”
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