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.
