Fix epoll_pwait2 feature detection#184
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The Termux Android build can expose an epoll_pwait2 symbol while omitting the corresponding declaration from <sys/epoll.h>. The previous mkmf probe only checked whether the symbol could be linked, so extconf.rb generated HAVE_EPOLL_PWAIT2 even though epoll.c could not compile a real call to the function under C99 implicit-declaration rules. Probe epoll_pwait2 using the same header and a concrete call expression instead. This keeps HAVE_EPOLL_PWAIT2 enabled on platforms where the header declares the API, while allowing Android/Termux to fall back to the existing epoll_wait path. Closes #155
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TL;DR
Fix
epoll_pwait2feature detection so Android/Termux can fall back toepoll_waitwhen the header does not declareepoll_pwait2.Context
Closes #155
The reported Termux build has a linkable
epoll_pwait2symbol, so mkmf's barehave_func("epoll_pwait2")probe can defineHAVE_EPOLL_PWAIT2. However, Android's<sys/epoll.h>in that environment does not declareepoll_pwait2, so compilingepoll.cfails with an implicit function declaration error under C99.Changes
The probe now checks an
epoll_pwait2(0, 0, 0, 0, 0)call expression through<sys/epoll.h>. This keeps the generated macro asHAVE_EPOLL_PWAIT2while requiring the declaration to be visible to the compiler.Platforms whose headers expose the API still use
epoll_pwait2; Android/Termux configurations that only expose the symbol leave the macro undefined and continue using the existingepoll_waitfallback.Tophatting
bundle exec rubocop -Aruby ext/extconf.rbThe local extconf run reports
checking for epoll_pwait2(0, 0, 0, 0, 0) in sys/epoll.h... noon this machine, which matches the intended header-aware fallback behavior when the declaration is unavailable.