On Wed, 31 May 2023 at 21:27, J.W. Jagersma <jwjagersma@xxxxxxxxx> wrote: > > On 2023-05-31 22:24, Jonathan Wakely wrote: > > On Wed, 31 May 2023 at 21:23, J.W. Jagersma <jwjagersma@xxxxxxxxx> wrote: > >> > >> On 2023-05-31 22:18, Jonathan Wakely wrote: > >>> On Wed, 31 May 2023 at 21:15, J.W. Jagersma via Gcc-help > >>> <gcc-help@xxxxxxxxxxx> wrote: > >>>> > >>>> Hi all, > >>>> > >>>> In my cooperative scheduler I currently use a regular exception type for thread > >>>> cancellation. But these tend to get eaten, for example by std::iosteam > >>>> functions. > >>>> > >>>> Now I see those functions do catch and rethrow a __cxxabiv1::__forced_unwind > >>>> type, and I presume such an object can be thrown via _Unwind_ForcedUnwind(). > >>>> > >>>> But how do you actually use it? > >>> > >>> You don't. It exists for pthread_kill, not for users. > >>> > >>>> Specifically, how is the exception supposed to > >>>> be allocated, who is in charge of freeing it, > >>> > >>> The runtime does that as needed. > >>> > >>>> and how do you make sure it stops > >>>> where you want it to? > >>> > >>> You can't, it can never be stopped. If it is caught and not rethrown > >>> then the entire process is aborted. It must propagate to the initial > >>> function that was executed in the thread, and then when it leaves that > >>> function the thread is terminated. > >> > >> Okay, that's a bit unfortunate. But why is it exposed in a public header then > >> if it's never supposed to be used by anyone? > >> > >> I understand doing something like this from user code is extremely messy, > >> but... that's how these things are. > > > > Why not just use pthread_kill(0) if you want a __forced_unwind exception? > > Single-threaded target, I don't have pthreads. That's why I rolled my own. Then you couldn't use __forced_unwind anyway, it would always terminate the program.
