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Fall back to epoll_wait when epoll_pwait2 is unavailable at runtime #23825

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Fall back to epoll_wait when epoll_pwait2 is unavailable at runtime #23825

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21 changes: 17 additions & 4 deletions main/poll/poll_backend_epoll.c
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,11 @@

#include <sys/epoll.h>

#ifdef HAVE_EPOLL_PWAIT2
/* Cleared when the running kernel returns ENOSYS */
static zend_atomic_bool epoll_pwait2_available = ZEND_ATOMIC_BOOL_INITIALIZER(true);
#endif

typedef struct epoll_backend_data {
int epoll_fd;
struct epoll_event *events;
Expand Down Expand Up @@ -182,11 +187,19 @@ static int epoll_backend_wait(

int nfds;
#ifdef HAVE_EPOLL_PWAIT2
nfds = epoll_pwait2(backend_data->epoll_fd, backend_data->events, max_events, timeout, NULL);
#else
int timeout_ms = php_poll_timespec_to_ms(timeout);
nfds = epoll_wait(backend_data->epoll_fd, backend_data->events, max_events, timeout_ms);
if (EXPECTED(zend_atomic_bool_load_ex(&epoll_pwait2_available))) {
nfds = epoll_pwait2(
backend_data->epoll_fd, backend_data->events, max_events, timeout, NULL);
if (UNEXPECTED(nfds < 0 && (errno == ENOSYS || errno == ENOTSUP))) {
zend_atomic_bool_store_ex(&epoll_pwait2_available, false);
}
}
if (UNEXPECTED(!zend_atomic_bool_load_ex(&epoll_pwait2_available)))
#endif
{
int timeout_ms = php_poll_timespec_to_ms(timeout);
nfds = epoll_wait(backend_data->epoll_fd, backend_data->events, max_events, timeout_ms);
}

if (nfds > 0) {

@devnexen devnexen Sep 21, 2026 •
edited
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nit: I get 'ndfs' may be unitialized [-Wmaybe-uninitialized].

for (int i = 0; i < nfds; i++) {
Expand Down
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