Kevin Wolf <kw...@redhat.com> writes: > Am 17.01.2020 um 06:44 hat Markus Armbruster geschrieben: >> Kevin Wolf <kw...@redhat.com> writes: >> >> > Am 16.01.2020 um 16:13 hat Markus Armbruster geschrieben: >> >> Kevin Wolf <kw...@redhat.com> writes: >> >> >> >> > Am 16.01.2020 um 10:45 hat Markus Armbruster geschrieben: [...] >> >> >> Pardon my ignorant question: what exactly makes a function a >> >> >> coroutine_fn? >> >> > >> >> > When Stefan requested adding the coroutine_fn marker, it seemed to make >> >> > sense to me because the QMP dispatcher will always call it from >> >> > coroutine context now, and being always run in coroutine context makes a >> >> > function a coroutine_fn. >> >> > >> >> > However, it's also called from hmp_block_resize(), so at least for now >> >> > coroutine_fn is actually wrong. >> >> >> >> This answers the question when we mark a function a coroutine_fn. I >> >> meant to ask what conditions the function itself must satisfy to be >> >> eligible for this mark. >> > >> > The requirement is actually not about the function itself, it's about >> > the callers, as stated above. >> > >> > But being a coroutine_fn allows the function to call other functions >> > that only work in coroutine context (other coroutine_fns). In the end >> > the reason why a function only works in coroutine context is usually >> > that it (or any other coroutine_fns called by it) could yield, which >> > obviously doesn't work outside of coroutine contest. >> >> Thanks. >> >> I think "being always run in coroutine context makes a function a >> coroutine_fn" is inaccurate. It's "calling a coroutine_fn without >> switching to coroutine context first when not already in coroutine >> context". The induction terminates at basic coroutine_fn like >> qemu_coroutine_yield(). > > I think we would tend to mark things as coroutine_fn even if they don't > call other coroutine_fns (yet), but would be allowed to. But this is now > really splitting hairs.
Your hair-splitting is my education :) > Maybe I should just have referred to the documentation in the source: > > /** > * Mark a function that executes in coroutine context > * > * Functions that execute in coroutine context cannot be called directly from > * normal functions. In the future it would be nice to enable compiler or > * static checker support for catching such errors. This annotation might > make > * it possible and in the meantime it serves as documentation. > * > * For example: > * > * static void coroutine_fn foo(void) { > * .... > * } > */ > #define coroutine_fn I had read that, of course, but it didn't quite enlighten me, so I asked. Perhaps it would have if it said "Mark a function that expects to run in coroutine context".