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Re: Throwing c++ exception across threads


Eric Lilja wrote:

The things is that the connection code may cause an exception and I want to run that in the connection thread so the UI doesn't freeze while it's waiting for an connection attempt to time-out for instance.

Exceptions are a stack unwinding mechanism, and each thread has its own stack. So no, threads are not normally thrown across threads, and if an exception 'escapes' from a thread context, it will call std::unexpected() and terminate the program, assuming you're using C++. Something similar will happen with SEH or other sorts of exceptions.


A primary reason this effect isn't going to work easily is that it would involve the 'main thread' being interrupted asynchronously, while it may be in the middle of doing something else, and being unwound by the exception handler. In general, this is not possible; C++ exceptions may only be thrown by certain contexts.

There may be various esoteric ways to get what you want, if you really wanted it; but the reality is that you almost certainly don't. The strength of exceptions is in unwinding the stack and calling automatic destructors. Using exceptions for general inter-thread communications is not appropriate.

As alternatives, I'd suggest:
-Have the main thread wait on the child thread.
-Set a condition variable.
-Release a mutex.

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