TraceSource and TraceListener quietly fail to do anything - system.diagnostics

Question

How do I troubleshoot System.Diagnostics trace when it quietly fails to do anything at all?

Answer 1

I'm so glad you asked! This problem happened to me recently. I suspected something in the chain of TraceSwitches, TraceSources and TraceListeners had gone awry. But with no trace and no error messages, I needed more information. The authors of the BCL helpfully put all the diagnostic information in a private list whose values disappear when ever the garbage collector feels like it. Still, the info was good enough and accessible via reflection. It turned out that I had several TraceSource's but the one in question didn't have a Switch set to something other than Off. (Another bad sign would be no listeners or only the "Default" listener)
This is the Page_Load event for a page with a label called DumpText. I'm sure this code could be adapted for Console or WinForms.
protected void Page_Load(object sender, EventArgs e)
{
TraceSource ts = new TraceSource("foo");
List<WeakReference> list = (List<WeakReference>)GetInstanceField(typeof(TraceSource), ts, "tracesources");
Dictionary<string, TraceSource> sources = new Dictionary<string, TraceSource>();
foreach (var weakReference in list)
{
if (!weakReference.IsAlive) continue;
TraceSource source = (weakReference.Target as TraceSource);
if (source == null || source.Name == "foo") continue;
if (sources.ContainsKey(source.Name)) continue;
sources.Add(source.Name, source);
}
StringBuilder sb = new StringBuilder();
foreach (KeyValuePair<string,TraceSource> kvp in sources.OrderBy((x) => x.Key))
{
TraceSource source = kvp.Value;
if (source == null)
{
continue;
}
sb.Append("<h3>");
sb.Append(source.Name);
sb.Append(" - ");
sb.Append(source.Switch.Level);
sb.Append("</h3>");
if (source.Switch.Level == SourceLevels.Off)
{
continue;
}
foreach (TraceListener l in source.Listeners)
{
sb.Append(l.Name);
sb.Append(" - ");
sb.Append(l.GetType().ToString());
sb.Append("<br/>");
foreach (string att in l.Attributes.Values)
{
sb.Append(" ");
sb.Append(att);
sb.Append(",");
}
}
sb.Append("<br/>");
}
this.DumpText.Text = sb.ToString();
}
internal static object GetInstanceField(Type type, object instance, string fieldName)
{
BindingFlags bindFlags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic
| BindingFlags.Static;
FieldInfo field = type.GetField(fieldName, bindFlags);
return field.GetValue(instance);
}