On 2023-05-31 22:28, Jonathan Wakely wrote: > 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. But _Unwind_ForcedUnwind() does take a pointer to a "stop" function, what does that do then?
