C# 4 and .NET 4

468 ❘ ChaPTer 19 instrumentAtiOn
Trace sources
You can write trace messages with the TraceSource class. Tracing requires the Trace fl ag of the compiler
settings. With a Visual Studio project, the Trace fl ag is set by default with debug and release builds, but you
can change it through the Build properties of the project.
T he TraceSource class is more diffi cult to use compared to the Trace class writing
trace messages, but it provides more options.
To write trace messages, you need to create a new TraceSource instance. In the constructor, the name of
the trace source is defi ned. The method TraceInformation() writes an information message to the trace
output. Instead of just writing informational messages, the TraceEvent() method requires an enumeration
value of type TraceEventType to defi ne the type of the trace message. TraceEventType.Error specifi es the
message as an error message. You can defi ne it with a trace switch to see only error messages. The second
argument of the TraceEvent() method requires an identifi er. The ID can be used within the application
itself. For example, you can use id 1 for entering a method and id 2 for exiting a method. The method
TraceEvent() is overloaded, so the TraceEventType and the ID are the only required parameters.
Using the third parameter of an overloaded method, you can pass the message written to the trace.
TraceEvent() also supports passing a format string with any number of parameters in the same way as
Console.WriteLine() . TraceInformation() does nothing more than invoke TraceEvent() with an
identifi er of 0. TraceInformation() is just a simplifi ed version of TraceEvent() . With the TraceData()
method, you can pass any object, for example, an exception instance, instead of a message. To make sure
that data is written by the listeners and does not stay in memory, you need to do a Flush() . If the source
is no longer needed, you can invoke the Close() method that closes all listeners associated with the trace
source. Close() does a Flush() as well.
public class Program
{
internal static TraceSource trace =
new TraceSource("Wrox.ProCSharp.Instrumentation");
static void TraceSourceDemo1()
{
trace.TraceInformation("Info message");
}
trace.TraceEvent(TraceEventType.Error, 3, "Error message");
trace.TraceData(TraceEventType.Information, 2, "data1", 4, 5);
trace.Flush();
trace.Close();
code snippet TracingDemo/Program.cs
You can use different trace sources within your application. It makes sense to defi ne
different sources for different libraries, so that you can turn on different trace levels
for different parts of your application. To use a trace source, you need to know its name.
A commonly used name for the trace source is the same name as the assembly name.
The TraceEventType enumeration that is passed as an argument to the TraceEvent() method
defi nes the following levels to specify the severity of the problem: Verbose , Information , Warning , Error ,
and Critical . Critical defi nes a fatal error or application crash; Error defi nes a recoverable error. Trace
messages at the Verbose level give you detailed debugging information. TraceEventType also defi nes
action levels Start , Stop , Suspend , and Resume . These levels defi ne timely events inside a logical operation.
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