Question

I have a non-blocking function (it returns immediately) that creates a new thread to parse some data:

boost::any Parse() throw(ParseException) {
  // parse something
}
typedef void (*HandlerFunc)(boost::any result);
void ParseAsync(HandlerFunc handler) {
  Parser me(*this);
  in_new_thread {
    boost::any result = me.Parse();
    handler(result);
  }
}

The problem is that Parse can throw an exception. What is the usual C++ way of handling these exceptions? Should I in some way “hand over” the exception to the handler function?

Answer 1

The new C++11 standard support a number of facilities to ease thread programming.

The most interesting, in your case, are std::future and std::promise.

Note the std::promise::set_exception_* function. It allows you to channel an exception outside of its thread of origin (note std::exception_ptr has a shared pointer semantics). You can use std::current_exception() (in a catch statement) to get the required pointer.

Then note the std::future::get function: if the promise the future is extracted from had an exception instead of a value, then it will throw the exception.

This is the mechanism in place to channel exceptions from one thread to another.