threads.h: use clock_monotonic for timeouts on posix if available

Prevents threads from timing out too early or too late if the system
clock is adjusted while waiting.

src/aclocal.m4

@@ -934,7 +934,7 @@ AC_CHECK_FUNC( [pthread_rwlock_init], [
     AC_DEFINE([HAVE_POSIX_RWLOCK], [], [HAVE_POSIX_RWLOCK])
   ], [])
 ], [])
-AC_CHECK_FUNCS([pthread_mutex_timedlock])
+AC_CHECK_FUNCS([pthread_mutex_timedlock pthread_condattr_setclock])
 ])
 
 

src/configure

@@ -6233,12 +6233,13 @@ fi
 
 fi
 
-for ac_func in pthread_mutex_timedlock
+for ac_func in pthread_mutex_timedlock pthread_condattr_setclock
 do :
-  ac_fn_c_check_func "$LINENO" "pthread_mutex_timedlock" "ac_cv_func_pthread_mutex_timedlock"
-if test "x$ac_cv_func_pthread_mutex_timedlock" = xyes; then :
+  as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
+ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
+if eval test \"x\$"$as_ac_var"\" = x"yes"; then :
   cat >>confdefs.h <<_ACEOF
-#define HAVE_PTHREAD_MUTEX_TIMEDLOCK 1
+#define `$as_echo "HAVE_$ac_func" | $as_tr_cpp` 1
 _ACEOF
 
 fi
@@ -9664,7 +9665,7 @@ done
 
 for ac_func in nanosleep alarm times select setenv putenv \
                 lstat mkstemp sigprocmask isatty tzset \
-                gettimeofday getrusage system
+                gettimeofday getrusage system clock_gettime
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"

src/configure.ac

@@ -754,7 +754,7 @@ dnl !!! end autoscan
 
 AC_CHECK_FUNCS( [nanosleep alarm times select setenv putenv] \
                 [lstat mkstemp sigprocmask isatty tzset] \
-                [gettimeofday getrusage system] )
+                [gettimeofday getrusage system clock_gettime] )
 
 AC_CHECK_FUNCS( [expf powf logf sqrtf cosf sinf tanf sinhf coshf tanhf] \
                 [floorf ceilf fabsf frexpf ldexpf log1p log1pf log1pl] \

src/ecl/configpre.h

@@ -192,6 +192,9 @@
 /* Define to 1 if you have the `cimagl' function. */
 #undef HAVE_CIMAGL
 
+/* Define to 1 if you have the `clock_gettime' function. */
+#undef HAVE_CLOCK_GETTIME
+
 /* Define to 1 if you have the `clog' function. */
 #undef HAVE_CLOG
 
@@ -436,6 +439,9 @@
 /* Define to 1 if you have the `powf' function. */
 #undef HAVE_POWF
 
+/* Define to 1 if you have the `pthread_condattr_setclock' function. */
+#undef HAVE_PTHREAD_CONDATTR_SETCLOCK
+
 /* Define to 1 if you have the `pthread_mutex_timedlock' function. */
 #undef HAVE_PTHREAD_MUTEX_TIMEDLOCK
 

src/h/config-internal.h.in

@@ -72,6 +72,8 @@
 #endif
 /* gettimeofday() and sys/time.h					*/
 #undef HAVE_GETTIMEOFDAY
+/* clock_gettime()							*/
+#undef HAVE_CLOCK_GETTIME
 /* getrusage() and sys/resource.h					*/
 #ifndef NACL
 #undef HAVE_GETRUSAGE
@@ -133,6 +135,8 @@
 #undef HAVE_POSIX_RWLOCK
 /* whether we have mutex lock operations with timeout                   */
 #undef HAVE_PTHREAD_MUTEX_TIMEDLOCK
+/* whether we can set the clock for timed waits on condition variables  */
+#undef HAVE_PTHREAD_CONDATTR_SETCLOCK
 /* uname() for system identification                                    */
 #undef HAVE_UNAME
 #undef HAVE_UNISTD_H

src/h/threads.h

@@ -37,6 +37,12 @@
 #define ECL_MUTEX_TIMEOUT ETIMEDOUT
 #define ECL_MUTEX_DEADLOCK EDEADLK
 
+#if defined(HAVE_PTHREAD_CONDATTR_SETCLOCK) && defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC)
+# define COND_VAR_CLOCK CLOCK_MONOTONIC
+#else
+# define COND_VAR_CLOCK CLOCK_REALTIME
+#endif
+
 /* MUTEX */
 
 /* Non-recursive locks are only provided as an optimization; on
@@ -83,15 +89,21 @@ ecl_mutex_lock(ecl_mutex_t *mutex)
 /* CONDITION VARIABLE */
 
 static inline void
-add_timeout_delta(struct timespec *ts, double seconds)
+add_timeout_delta(struct timespec *ts, double seconds, clockid_t preferred_clock)
 {
-#if defined(HAVE_GETTIMEOFDAY)
+#if defined(HAVE_CLOCK_GETTIME)
+  clock_gettime(preferred_clock, ts);
+#elif defined(HAVE_GETTIMEOFDAY)
   struct timeval tp;
 
   gettimeofday(&tp, NULL);
   /* Convert from timeval to timespec */
   ts->tv_sec  = tp.tv_sec;
   ts->tv_nsec = tp.tv_usec * 1000;
+#else
+  ts->tv_sec = time(NULL);
+  ts->tv_nsec = 0;
+#endif
 
   /* Add `seconds' delta */
   ts->tv_sec += (time_t)floor(seconds);
@@ -100,10 +112,6 @@ add_timeout_delta(struct timespec *ts, double seconds)
     ts->tv_nsec -= 1e9;
     ts->tv_sec++;
   }
-#else
-  ts->tv_sec = time(NULL) + (time_t)floor(seconds);
-  ts->tv_nsec = 0;
-#endif
 }
 
 static inline int
@@ -111,7 +119,12 @@ ecl_mutex_timedlock(ecl_mutex_t *mutex, double seconds)
 {
 #if defined(HAVE_PTHREAD_MUTEX_TIMEDLOCK)
   struct timespec ts;
-  add_timeout_delta(&ts, seconds);
+  /* Ideally we would like to use CLOCK_MONOTONIC here to prevent
+     wrong timeouts when the system clock is adjusted while we are
+     waiting. However the posix spec says that pthread_mutex_timedlock
+     always uses CLOCK_REALTIME and does not define a way to set the
+     clock for mutexes. */
+  add_timeout_delta(&ts, seconds, CLOCK_REALTIME);
   return pthread_mutex_timedlock(mutex, &ts);
 #else
   /* Not implemented, see mutex.d for alternative implementation using interrupts */
@@ -122,7 +135,13 @@ ecl_mutex_timedlock(ecl_mutex_t *mutex, double seconds)
 static inline void
 ecl_cond_var_init(ecl_cond_var_t *cv)
 {
-  pthread_cond_init(cv, NULL);
+  pthread_condattr_t attr;
+  pthread_condattr_init(&attr);
+#if defined(HAVE_PTHREAD_CONDATTR_SETCLOCK)
+  pthread_condattr_setclock(&attr, COND_VAR_CLOCK);
+#endif
+  pthread_cond_init(cv, &attr);
+  pthread_condattr_destroy(&attr);
 }
 
 static inline void
@@ -141,7 +160,7 @@ static inline int
 ecl_cond_var_timedwait(ecl_cond_var_t *cv, ecl_mutex_t *mutex, double seconds)
 {
   struct timespec ts;
-  add_timeout_delta(&ts, seconds);
+  add_timeout_delta(&ts, seconds, COND_VAR_CLOCK);
   return pthread_cond_timedwait(cv, mutex, &ts);
 }