The IErrorHandler interface in WCF allows to write some central error handling code that gets invoked whenever an unhandled exception bubbles up from your service. There are two methods to implement:

• ProvideFault – called on the request thread to turn the exception into a fault message
• HandleError – called on a separate thread for error logging and the like

While WCF tries its best to shield the service host from all kinds of error conditions, there are some situations where unhandled exceptions can hurt your hosting process. One of them is the HandleError method on IErrorHandler.

HandleError is called on a background thread to allow doing (kind of) lenghty operations without impacting the request where the error originally occurred. If you have an unhandled exception in HandleError the normal CLR rules for excpetions in background threads apply – which means shutting down the process. Be careful here.