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Re: Throwing c++ exception across threads


Eric Lilja wrote:

[...] Any messages are displayed in an editbox. If a severe error occurs, an exception is thrown. Will there be any problems if I catch these exceptions in the main thread? [...]

Just thinking about that setup makes my head spin. Yes, I suspect there'll be lots of problems if you do this. :-)


The very concept of "catching the exception in main" is absurd when threads are involved: the whole point of exception catching and throwing is that it is totally synchronous, and goes from callee to caller (to its caller and so on, until your main()).

All of this only makes sense in the context of one thread. Implicit in the catching of an exception is the idea that the exception was thrown from _something you called from within that try block_.

Otherwise, you'd have a situation like:

/* parent: */
   func() {
      ...
      // spawn thread
      return;  //!!
   }

   main()
   {
     ...
     func();
     ...
     some_other_random_stuff();
   }

/* child: */
   ...
   throw something;
   ...

Err, but the point from where the thread was created is no longer on the stack, because control returned to the parent and then went on somewhere else. So even if you attempted to do something bizarre like "hop stacks to the parent thread's stack", you'd end up in some random stack frame in the parent thread, like "some_other_random_stuff()", which won't be expecting that exception and won't know what to do with it...


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