Unhandled Exceptions

In the AMPS C++ client, exceptions can occur that are not thrown to the main thread of the application. For example, when an exception is thrown from a message handler running on a background thread, AMPS does not automatically propagate that exception to the main thread.

Instead, AMPS provides the exception to an unhandled exception handler if one is specified on the client. The unhandled exception handler receives a reference to the exception object, and takes whatever action is necessary. Typically, this involves logging the exception or setting an error flag that the main thread can act on. Notice that AMPS C++ client only catches exceptions that derive from std::exception. If your message handler contains code that can throw exceptions that do not derive from std::exception, 60East recommends catching these exceptions and throwing an equivalent exception that derives from std::exception.

If your application will attempt to recover from an exception thrown on the background processing thread, your application should set a flag and attempt recovery on a different thread than the thread that called the exception listener.

At the point that the AMPS client calls the exception listener, it has handled the exception. Your exception listener must not rethrow the exception (or wrap the exception and throw a different exception type).

For example, the unhandled exception handler below takes a std::ostream, and logs information from each exception to that std::ostream.

class ExceptionLogger : public AMPS::ExceptionListener
{
private:
    std::ostream& os_;

public:

    ExceptionLogger() : os_(std::cout) {}
    ExceptionLogger(std::ostream& os) : os_(os) {}

    virtual void exceptionThrown(const std::exception& e) const
    {
       os_ << e.what() << std::endl;
    }
}