Doing a runtime check in configure.ac (AC_RUN_IFELSE) has several
disadvantages:
* It doesn't work when cross-compiling. For example, if we build macOS
binaries on a Linux system, we'd assume that poll() works, but in
fact it won't.
* It checks the build system capabilities, but that is not necessarily
appropriate if (for example) a macOS 10.10 user builds binaries that
could be used by macOS 10.12 or macOS 10.9 users.
* It checks for one specific failure mode, but macOS seems to have a
history of various implementation issues in poll().
* If we want it to work in CMake, we have to duplicate it in the CMake
build system.
None of these is a showstopper on its own, but the combination of all
of them makes the current approach to avoiding the broken poll() on
macOS look unreliable. libcurl, a widely-portable library making
extensive use of sockets, specifically doesn't use poll() on Darwin
(macOS, iOS, etc.) or on Interix; let's follow their example here.
See also https://bugzilla.gnome.org/show_bug.cgi?id=302672 and
https://daniel.haxx.se/blog/2016/10/11/poll-on-mac-10-12-is-broken/
for some relevant history.
Signed-off-by: Simon McVittie <smcv@collabora.com>
Resolves: https://gitlab.freedesktop.org/dbus/dbus/issues/232
(cherry picked from commit
0414ea65ca8196e328da09c3a2324d7765fba8c4)
AC_CHECK_HEADERS_ONCE([sys/prctl.h])
AC_CHECK_FUNCS_ONCE([prctl raise])
-#### Check for broken poll; taken from Glib's configure
-
-AC_MSG_CHECKING([for broken poll])
-AC_RUN_IFELSE([AC_LANG_SOURCE([[
- #include <stdlib.h>
- #include <fcntl.h>
- #include <poll.h>
- #ifdef HAVE_SYS_POLL_H
- #include <sys/poll.h>
- #endif
- int main(void) {
- struct pollfd fds[1];
- int fd;
- fd = open("/dev/null", 1);
- fds[0].fd = fd;
- fds[0].events = POLLIN;
- fds[0].revents = 0;
- if (poll(fds, 1, 0) < 0 || (fds[0].revents & POLLNVAL) != 0) {
- exit(1); /* Does not work for devices -- fail */
- }
- exit(0);
- }]])],
- [broken_poll=no],
- [broken_poll=yes
- AC_DEFINE(BROKEN_POLL,1,[poll doesn't work on devices])],
- [broken_poll="no (cross compiling)"])
-AC_MSG_RESULT($broken_poll)
-
AC_MSG_CHECKING(for dirfd)
AC_LINK_IFELSE([AC_LANG_PROGRAM([[
#include <sys/types.h>
#include <string.h>
#include <stdarg.h>
+#if !defined(BROKEN_POLL) && (defined(__APPLE__) || defined(__INTERIX))
+ /* Following libcurl's example, we blacklist poll() on Darwin
+ * (macOS, iOS, etc.) and Interix due to a history of implementation
+ * issues.
+ * https://github.com/curl/curl/blob/master/m4/curl-functions.m4
+ *
+ * On unspecified older macOS versions, poll() failed if given a
+ * device node to poll.
+ *
+ * On macOS < 10.9, poll() with nfds=0 failed instead of waiting for
+ * the timeout and then succeeding.
+ *
+ * On macOS >= 10.12, poll() with nfds=0 succeeded immediately
+ * instead of waiting for the timeout, resulting in busy-looping.
+ *
+ * On Interix, poll() apparently only works for files in /proc.
+ *
+ * The "legacy" build flavour in our CI machinery defines BROKEN_POLL
+ * on whatever platform is in use (normally Linux) to force use of the
+ * same select()-based poll() emulation that we use for macOS, Interix,
+ * and any platform that lacks a real poll(), so that we can test it
+ * more regularly.
+ */
+# define BROKEN_POLL
+#endif
+
/* AIX sys/poll.h does #define events reqevents, and other
* wonderousness, so must include sys/poll before declaring
* DBusPollFD