eventbrokerexceptionhandling.html

---
layout: documentation 
title: EventBroker 
teaser: Decoupled eventing with automatic thread switching
navigation:
   - name: Overview
     link: eventbroker.html
   - name: Tutorial
     link: eventbrokertutorial.html	
   - name: Registration by Attribute
     link: eventbrokerregistrationbyattribute.html
   - name: Registration over Interface
     link: eventbrokerregistrationoverinterface.html
   - name: Registration by Registrar
     link: eventbrokerregistrationbyregistrar.html
   - name: Simplified Handler Methods
     link: eventbrokersimplifiedhandlermethods.html
   - name: Direct Interaction
     link: eventbrokerdirectinteraction.html
   - name: Handlers
     link: eventbrokerhandlers.html
   - name: Matchers
     link: eventbrokermatchers.html
   - name: Exception Handling
     link: eventbrokerexceptionhandling.html
   - name: Extensions
     link: eventbrokerextensions.html
   - name: Logging
     link: eventbrokerlogging.html
   - name: Testability
     link: eventbrokertestability.html
   - name: Tips and Tricks
     link: eventbrokertipsandtricks.html
   - name: Specifications
     link: eventbrokerspecifications.html		 
---
<h2>Exception Handling</h2>

<h3>Exceptions thrown by the Event Broker</h3>
<p>
The event broker will throw an exception during registration when
<ul>
  <li>the publisher or subscriber was already registered for the event topic</li>
  <li>the publisher and subscriber do not match (handler restrictions, publisher event args not assignable to subscriber event args</li>
  <li>the event or handler method signature cannot be handled</li>
</ul>
</p>


<h3>Exceptions thrown by Subscribers</h3>
<p>
When a subscriber throws an exception while handling an event it depends on whether the handler is synchronous or asynchronous.
An exception thrown by a synchronous handler is passed to the publisher. 
An exception of an asynchronous handler can only be catched by the global .net background thread exception handler.
</p>
<p>
You can get better control over exception throwing subscribers by implementing an 
<a href="eventbrokerextensions.html">extension</a>. All built-in handlers call 
<code>SubscriberExceptionOccurred</code> on all extensions. An extension can then mark the exception as handled
and the event broker won't re-throw the exception.
</p>