On GNU/Linux, use timerfd for asynchronous timers.

* configure.ac (toplevel): Check whether GNU/Linux-specific
timerfd functions and macros are available.
* m4/clock_time.m4 (gl_CLOCK_TIME): Check for clock_getres as well.
* src/atimer.c (toplevel) [HAVE_TIMERFD]: Include sys/timerfd.h.
(toplevel): Rename alarm_timer_ok to special_timer_available.
[HAVE_TIMERFD]: Declare timerfd.
[HAVE_CLOCK_GETRES]: Declare resolution.
(start_atimer) [HAVE_CLOCK_GETRES]: Round up timestamp to
system timer resolution.
(set_alarm) [HAVE_TIMERFD]: Use timerfd_settime.
(timerfd_callback) [HAVE_TIMERFD]: New function.
(atimer_result, debug_timer_callback, Fdebug_timer_check)
[ENABLE_CHECKING]: New function for the sake of automated tests.
(init_atimer) [HAVE_TIMERFD]: Setup timerfd.
[HAVE_CLOCK_GETRES]: Likewise for system timer resolution.
[ENABLE_CHECKING]: Defsubr test function.
* src/atimer.h (timerfd_callback) [HAVE_TIMERFD]: Add prototype.
* src/lisp.h (add_timer_wait_descriptor) [HAVE_TIMERFD]: Likewise.
* src/process.c (add_timer_wait_descriptor) [HAVE_TIMERFD]: New function.
* test/automated/timer-tests.el (timer-tests-debug-timer-check): New test.

1 files changed, 18 insertions, 0 deletions

diff --git a/src/process.c b/src/process.c
index 4449493a2b6..cfc1e189cab 100644
--- a/src/process.c
+++ b/src/process.c
@@ -6827,6 +6827,24 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
 /* The following functions are needed even if async subprocesses are
    not supported.  Some of them are no-op stubs in that case.  */
 
+#ifdef HAVE_TIMERFD
+
+/* Add FD, which is a descriptor returned by timerfd_create,
+   to the set of non-keyboard input descriptors.  */
+
+void
+add_timer_wait_descriptor (int fd)
+{
+  FD_SET (fd, &non_keyboard_wait_mask);
+  fd_callback_info[fd].func = timerfd_callback;
+  fd_callback_info[fd].data = NULL;
+  fd_callback_info[fd].condition |= FOR_READ;
+  if (fd > max_input_desc)
+    max_input_desc = fd;
+}
+
+#endif /* HAVE_TIMERFD */
+
 /* Add DESC to the set of keyboard input descriptors.  */
 
 void