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.

10 files changed, 222 insertions, 15 deletions

diff --git a/ChangeLog b/ChangeLog
index f694a42202..c7fd47636a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2014-07-28  Dmitry Antipov  <dmantipov@yandex.ru>
+
+	* 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.
+
 2014-07-13  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Improve behavior of 'bzr up; cd src; make -k'.
diff --git a/configure.ac b/configure.ac
index fc7a87a075..89440446ee 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3710,6 +3710,26 @@ fi
 AC_SUBST(LIBS_TERMCAP)
 AC_SUBST(TERMCAP_OBJ)
 
+# GNU/Linux-specific timer functions.
+if test $opsys = gnu-linux; then
+  AC_MSG_CHECKING([whether Linux timerfd functions are supported])
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/timerfd.h>]],
+				     [[timerfd_create (CLOCK_REALTIME, 0);
+				       timerfd_settime (0, 0, NULL, NULL)]])],
+  emacs_cv_linux_timerfd=yes, emacs_cv_linux_timerfd=no)
+  AC_MSG_RESULT([$emacs_cv_linux_timerfd])
+  if test $emacs_cv_linux_timerfd = yes; then
+    AC_DEFINE(HAVE_TIMERFD, 1, [Define to 1 if Linux timerfd functions are supported.])
+    AC_MSG_CHECKING([whether TFD_CLOEXEC is defined])
+      AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/timerfd.h>]],
+					 [[timerfd_create (CLOCK_REALTIME, TFD_CLOEXEC)]])],
+    emacs_cv_tfd_cloexec=yes, emacs_cv_tfd_cloexec=no)
+    AC_MSG_RESULT([$emacs_cv_tfd_cloexec])
+    if test $emacs_cv_tfd_cloexec = yes; then
+      AC_DEFINE(HAVE_TIMERFD_CLOEXEC, 1, [Define to 1 if TFD_CLOEXEC is defined.])
+    fi
+  fi
+fi  
 
 # Do we have res_init, for detecting changes in /etc/resolv.conf?
 # On Darwin, res_init appears not to be useful: see bug#562 and
diff --git a/m4/clock_time.m4 b/m4/clock_time.m4
index 6c4a637dc6..8513c6d781 100644
--- a/m4/clock_time.m4
+++ b/m4/clock_time.m4
@@ -26,6 +26,6 @@ AC_DEFUN([gl_CLOCK_TIME],
     AC_SEARCH_LIBS([clock_gettime], [rt posix4],
                    [test "$ac_cv_search_clock_gettime" = "none required" ||
                     LIB_CLOCK_GETTIME=$ac_cv_search_clock_gettime])
-    AC_CHECK_FUNCS([clock_gettime clock_settime])
+    AC_CHECK_FUNCS([clock_getres clock_gettime clock_settime])
   LIBS=$gl_saved_libs
 ])
diff --git a/src/ChangeLog b/src/ChangeLog
index b3f3750df7..ebc412c886 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,23 @@
+2014-07-28  Dmitry Antipov  <dmantipov@yandex.ru>
+
+	On GNU/Linux, use timerfd for asynchronous timers.
+	* 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.
+	* atimer.h (timerfd_callback) [HAVE_TIMERFD]: Add prototype.
+	* lisp.h (add_timer_wait_descriptor) [HAVE_TIMERFD]: Likewise.
+	* process.c (add_timer_wait_descriptor) [HAVE_TIMERFD]: New function.
+
 2014-07-28  Paul Eggert  <eggert@cs.ucla.edu>
 
 	* frame.c (x_set_frame_parameters): Don't use uninitialized locals.
diff --git a/src/atimer.c b/src/atimer.c
index c4f062beb1..9079e7712e 100644
--- a/src/atimer.c
+++ b/src/atimer.c
@@ -26,6 +26,15 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include "atimer.h"
 #include <unistd.h>
 
+#ifdef HAVE_TIMERFD
+#include <sys/timerfd.h>
+#ifdef HAVE_TIMERFD_CLOEXEC
+#define TIMERFD_CREATE_FLAGS TFD_CLOEXEC
+#else
+#define TIMERFD_CREATE_FLAGS 0
+#endif /* HAVE_TIMERFD_CLOEXEC */
+#endif /* HAVE_TIMERFD */
+
 /* Free-list of atimer structures.  */
 
 static struct atimer *free_atimers;
@@ -40,11 +49,23 @@ static struct atimer *stopped_atimers;
 
 static struct atimer *atimers;
 
-/* The alarm timer and whether it was properly initialized, if
-   POSIX timers are available.  */
-#ifdef HAVE_ITIMERSPEC
+#if defined (HAVE_TIMERFD)
+/* File descriptor returned by timerfd_create.  GNU/Linux-specific.  */
+static int timerfd;
+#elif defined (HAVE_ITIMERSPEC)
+/* The alarm timer used if POSIX timers are available.  */
 static timer_t alarm_timer;
-static bool alarm_timer_ok;
+#endif
+
+#if defined (HAVE_TIMERFD) || defined (HAVE_ITIMERSPEC)
+/* Non-zero if one of the above was successfully initialized.  Do not
+   use bool due to special treatment if HAVE_TIMERFD, see below.  */
+static int special_timer_available;
+#endif
+
+#ifdef HAVE_CLOCK_GETRES
+/* Resolution of CLOCK_REALTIME clock.  */
+static struct timespec resolution;
 #endif
 
 /* Block/unblock SIGALRM.  */
@@ -96,11 +117,16 @@ start_atimer (enum atimer_type type, struct timespec timestamp,
   struct atimer *t;
   sigset_t oldset;
 
-  /* Round TIME up to the next full second if we don't have
-     itimers.  */
-#ifndef HAVE_SETITIMER
+#if !defined (HAVE_SETITIMER)
+  /* Round TIME up to the next full second if we don't have itimers.  */
   if (timestamp.tv_nsec != 0 && timestamp.tv_sec < TYPE_MAXIMUM (time_t))
     timestamp = make_timespec (timestamp.tv_sec + 1, 0);
+#elif defined (HAVE_CLOCK_GETRES)
+  /* Check that the system clock is precise enough.  If
+     not, round TIME up to the system clock resolution.  */
+  if (timespec_valid_p (resolution)
+      && timespec_cmp (timestamp, resolution) < 0)
+    timestamp = resolution;
 #endif /* not HAVE_SETITIMER */
 
   /* Get an atimer structure from the free-list, or allocate
@@ -285,16 +311,25 @@ set_alarm (void)
 #endif
       struct timespec now, interval;
 
-#ifdef HAVE_ITIMERSPEC
-      if (alarm_timer_ok)
+#if defined (HAVE_TIMERFD) || defined (HAVE_ITIMERSPEC)
+      if (special_timer_available)
 	{
 	  struct itimerspec ispec;
 	  ispec.it_value = atimers->expiration;
 	  ispec.it_interval.tv_sec = ispec.it_interval.tv_nsec = 0;
+#if defined (HAVE_TIMERFD)
+	  if (special_timer_available == 1)
+	    {
+	      add_timer_wait_descriptor (timerfd);
+	      special_timer_available++;
+	    }
+	  if (timerfd_settime (timerfd, TFD_TIMER_ABSTIME, &ispec, 0) == 0)
+#elif defined (HAVE_ITIMERSPEC)
 	  if (timer_settime (alarm_timer, TIMER_ABSTIME, &ispec, 0) == 0)
+#endif	    
 	    return;
 	}
-#endif
+#endif /* HAVE_TIMERFD || HAVE_ITIMERSPEC */
 
       /* Determine interval till the next timer is ripe.
 	 Don't set the interval to 0; this disables the timer.  */
@@ -373,6 +408,15 @@ handle_alarm_signal (int sig)
   pending_signals = 1;
 }
 
+#ifdef HAVE_TIMERFD
+
+void
+timerfd_callback (int fd, void *arg)
+{
+  do_pending_atimers ();
+}
+
+#endif /* HAVE_TIMERFD */
 
 /* Do pending timers.  */
 
@@ -401,21 +445,106 @@ turn_on_atimers (bool on)
     alarm (0);
 }
 
+/* This is intended to use from automated tests.  */
+
+#ifdef ENABLE_CHECKING
+
+#define MAXTIMERS 10
+
+struct atimer_result
+{
+  /* Time when we expect this timer to trigger.  */
+  struct timespec expected;
+
+  /* Timer status: -1 if not triggered, 0 if triggered
+     too early or too late, 1 if triggered timely.  */
+  int intime;
+};
+
+static void
+debug_timer_callback (struct atimer *t)
+{
+  struct timespec now = current_timespec ();
+  struct atimer_result *r = (struct atimer_result *) t->client_data;
+  int result = timespec_cmp (now, r->expected);
+
+  if (result < 0)
+    /* Too early.  */
+    r->intime = 0;
+  else if (result >= 0)
+    {
+#ifdef HAVE_SETITIMER      
+      struct timespec delta = timespec_sub (now, r->expected);
+      /* Too late if later than expected + 0.01s.  FIXME:
+	 this should depend from system clock resolution.  */
+      if (timespec_cmp (delta, make_timespec (0, 10000000)) > 0)
+	r->intime = 0;
+      else
+#endif /* HAVE_SETITIMER */	
+	r->intime = 1;
+    }
+}
+
+DEFUN ("debug-timer-check", Fdebug_timer_check, Sdebug_timer_check, 0, 0, 0,
+       doc: /* Run internal self-tests to check timers subsystem.
+Return t if all self-tests are passed, nil otherwise.  */)
+  (void)
+{
+  int i, ok;
+  struct atimer *timer;
+  struct atimer_result *results[MAXTIMERS];
+  struct timespec t = make_timespec (0, 0);
+
+  /* Arm MAXTIMERS relative timers to trigger with 0.1s intervals.  */
+  for (i = 0; i < MAXTIMERS; i++)
+    {
+      results[i] = xmalloc (sizeof (struct atimer_result));
+      t = timespec_add (t, make_timespec (0, 100000000));
+      results[i]->expected = timespec_add (current_timespec (), t);
+      results[i]->intime = -1;
+      timer = start_atimer (ATIMER_RELATIVE, t,
+			    debug_timer_callback, results[i]);
+    }
+
+  /* Wait for 1s but process timers.  */
+  wait_reading_process_output (1, 0, 0, false, Qnil, NULL, 0);
+  /* Shut up the compiler by "using" this variable.  */
+  (void) timer;
+
+  for (i = 0, ok = 0; i < MAXTIMERS; i++)
+    ok += results[i]->intime, xfree (results[i]);
+
+  return ok == MAXTIMERS ? Qt : Qnil;
+}
+
+#endif /* ENABLE_CHECKING */
 
 void
 init_atimer (void)
 {
-#ifdef HAVE_ITIMERSPEC
+#if defined (HAVE_TIMERFD)
+  timerfd = timerfd_create (CLOCK_REALTIME, TIMERFD_CREATE_FLAGS);
+  special_timer_available = !!(timerfd != -1);
+#elif defined (HAVE_ITIMERSPEC)
   struct sigevent sigev;
   sigev.sigev_notify = SIGEV_SIGNAL;
   sigev.sigev_signo = SIGALRM;
   sigev.sigev_value.sival_ptr = &alarm_timer;
-  alarm_timer_ok = timer_create (CLOCK_REALTIME, &sigev, &alarm_timer) == 0;
-#endif
+  special_timer_available
+    = timer_create (CLOCK_REALTIME, &sigev, &alarm_timer) == 0;
+#endif /* HAVE_TIMERFD */
+#ifdef HAVE_CLOCK_GETRES
+  if (clock_getres (CLOCK_REALTIME, &resolution))
+    resolution = invalid_timespec ();
+#endif  
   free_atimers = stopped_atimers = atimers = NULL;
 
   /* pending_signals is initialized in init_keyboard.  */
   struct sigaction action;
   emacs_sigaction_init (&action, handle_alarm_signal);
   sigaction (SIGALRM, &action, 0);
+
+#ifdef ENABLE_CHECKING
+  defsubr (&Sdebug_timer_check);
+#endif  
 }
diff --git a/src/atimer.h b/src/atimer.h
index 379787abca..2386977cf8 100644
--- a/src/atimer.h
+++ b/src/atimer.h
@@ -77,5 +77,8 @@ void init_atimer (void);
 void turn_on_atimers (bool);
 void stop_other_atimers (struct atimer *);
 void run_all_atimers (void);
+#ifdef HAVE_TIMERFD
+void timerfd_callback (int, void *);
+#endif
 
 #endif /* EMACS_ATIMER_H */
diff --git a/src/lisp.h b/src/lisp.h
index bf25f073d4..67299706c6 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4186,6 +4186,9 @@ extern int wait_reading_process_output (intmax_t, int, int, bool, Lisp_Object,
 #else
 # define WAIT_READING_MAX INTMAX_MAX
 #endif
+#ifdef HAVE_TIMERFD
+extern void add_timer_wait_descriptor (int);
+#endif
 extern void add_keyboard_wait_descriptor (int);
 extern void delete_keyboard_wait_descriptor (int);
 #ifdef HAVE_GPM
diff --git a/src/process.c b/src/process.c
index 4449493a2b..cfc1e189ca 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
diff --git a/test/ChangeLog b/test/ChangeLog
index 6afa9ea895..140b5d04ef 100644
--- a/test/ChangeLog
+++ b/test/ChangeLog
@@ -1,3 +1,7 @@
+2014-07-28  Dmitry Antipov  <dmantipov@yandex.ru>
+
+	* automated/timer-tests.el (timer-tests-debug-timer-check): New test.
+
 2014-07-26  Ulf Jasper  <ulf.jasper@web.de>
 
 	* automated/icalendar-tests.el (icalendar-tests--do-test-import):
diff --git a/test/automated/timer-tests.el b/test/automated/timer-tests.el
index bc95df5e77..f8e8414f8d 100644
--- a/test/automated/timer-tests.el
+++ b/test/automated/timer-tests.el
@@ -34,5 +34,9 @@
     (sit-for 0 t)
     (should timer-ran)))
 
-;;; timer-tests.el ends here
+(ert-deftest timer-tests-debug-timer-check ()
+  ;; This function exists only if --enable-checking.
+  (if (fboundp 'debug-timer-check)
+      (should (debug-timer-check)) t))
 
+;;; timer-tests.el ends here