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HAVE_EPOLL_PWAIT2 only tells whether the libc exports the wrapper, which glibc does since 2.35 regardless of the running kernel. A PHP built on a kernel with epoll_pwait2 and run on one older than 5.11 gets ENOSYS from every Context::wait() call, which makes the epoll backend and thus the Auto backend unusable. The same happens under emulation layers that do not implement the syscall. Try epoll_pwait2 first and on ENOSYS or ENOTSUP switch the process to epoll_wait with a millisecond timeout, retrying the current call so the failure is never visible to the caller. The flag is process wide since kernel support is the same for every thread, and it is atomic so the first concurrent waits in a ZTS build do not race on it.
devnexen
reviewed
Sep 21, 2026
| nfds = epoll_wait(backend_data->epoll_fd, backend_data->events, max_events, timeout_ms); | ||
| } | ||
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| if (nfds > 0) { |
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nit: I get 'ndfs' may be unitialized [-Wmaybe-uninitialized].
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HAVE_EPOLL_PWAIT2only means the libc exports the wrapper, which glibc does since 2.35 regardless of the running kernel. A PHP built on a kernel withepoll_pwait2and run on one older than 5.11 getsENOSYSfrom everyContext::wait(), which makes the epoll backend and thusBackend::Autounusable. This is the normal shape for Docker images, distro packages and static builds, and it also happens under emulation layers that lack the syscall, as seen in #23478.Try
epoll_pwait2first and onENOSYSorENOTSUPswitch the process toepoll_wait, retrying the current call so the caller never sees the error. The flag is process-wide and atomic so ZTS builds do not race on it.The configure check is unchanged, so the plain link check keeps working when cross-compiling.
Alternative to #23478.