6900441: PlatformEvent.park(millis) on Linux could still be affected by...

6900441: PlatformEvent.park(millis) on Linux could still be affected by changes to the time-of-day clock
Summary: Associate CLOCK_MONOTONIC with the pthread_cond_t objects used for relative timed waits
Reviewed-by: dcubed, shade

src/os/linux/vm/os_linux.cpp

@@ -131,6 +131,7 @@ bool os::Linux::_is_NPTL = false;
 bool os::Linux::_supports_fast_thread_cpu_time = false;
 const char * os::Linux::_glibc_version = NULL;
 const char * os::Linux::_libpthread_version = NULL;
+pthread_condattr_t os::Linux::_condattr[1];
 
 static jlong initial_time_count=0;
 
@@ -1399,12 +1400,15 @@ void os::Linux::clock_init() {
           clock_gettime_func(CLOCK_MONOTONIC, &tp)  == 0) {
         // yes, monotonic clock is supported
         _clock_gettime = clock_gettime_func;
+        return;
       } else {
         // close librt if there is no monotonic clock
         dlclose(handle);
       }
     }
   }
+  warning("No monotonic clock was available - timed services may " \
+          "be adversely affected if the time-of-day clock changes");
 }
 
 #ifndef SYS_clock_getres
@@ -4709,6 +4713,26 @@ void os::init(void) {
 
   Linux::clock_init();
   initial_time_count = os::elapsed_counter();
+
+  // pthread_condattr initialization for monotonic clock
+  int status;
+  pthread_condattr_t* _condattr = os::Linux::condAttr();
+  if ((status = pthread_condattr_init(_condattr)) != 0) {
+    fatal(err_msg("pthread_condattr_init: %s", strerror(status)));
+  }
+  // Only set the clock if CLOCK_MONOTONIC is available
+  if (Linux::supports_monotonic_clock()) {
+    if ((status = pthread_condattr_setclock(_condattr, CLOCK_MONOTONIC)) != 0) {
+      if (status == EINVAL) {
+        warning("Unable to use monotonic clock with relative timed-waits" \
+                " - changes to the time-of-day clock may have adverse affects");
+      } else {
+        fatal(err_msg("pthread_condattr_setclock: %s", strerror(status)));
+      }
+    }
+  }
+  // else it defaults to CLOCK_REALTIME
+
   pthread_mutex_init(&dl_mutex, NULL);
 
   // If the pagesize of the VM is greater than 8K determine the appropriate
@@ -5519,21 +5543,36 @@ void os::pause() {
 
 static struct timespec* compute_abstime(timespec* abstime, jlong millis) {
   if (millis < 0)  millis = 0;
-  struct timeval now;
-  int status = gettimeofday(&now, NULL);
-  assert(status == 0, "gettimeofday");
+
   jlong seconds = millis / 1000;
   millis %= 1000;
   if (seconds > 50000000) { // see man cond_timedwait(3T)
     seconds = 50000000;
   }
-  abstime->tv_sec = now.tv_sec  + seconds;
-  long       usec = now.tv_usec + millis * 1000;
-  if (usec >= 1000000) {
-    abstime->tv_sec += 1;
-    usec -= 1000000;
+
+  if (os::Linux::supports_monotonic_clock()) {
+    struct timespec now;
+    int status = os::Linux::clock_gettime(CLOCK_MONOTONIC, &now);
+    assert_status(status == 0, status, "clock_gettime");
+    abstime->tv_sec = now.tv_sec  + seconds;
+    long nanos = now.tv_nsec + millis * NANOSECS_PER_MILLISEC;
+    if (nanos >= NANOSECS_PER_SEC) {
+      abstime->tv_sec += 1;
+      nanos -= NANOSECS_PER_SEC;
+    }
+    abstime->tv_nsec = nanos;
+  } else {
+    struct timeval now;
+    int status = gettimeofday(&now, NULL);
+    assert(status == 0, "gettimeofday");
+    abstime->tv_sec = now.tv_sec  + seconds;
+    long usec = now.tv_usec + millis * 1000;
+    if (usec >= 1000000) {
+      abstime->tv_sec += 1;
+      usec -= 1000000;
+    }
+    abstime->tv_nsec = usec * 1000;
   }
-  abstime->tv_nsec = usec * 1000;
   return abstime;
 }
 
@@ -5625,7 +5664,7 @@ int os::PlatformEvent::park(jlong millis) {
     status = os::Linux::safe_cond_timedwait(_cond, _mutex, &abst);
     if (status != 0 && WorkAroundNPTLTimedWaitHang) {
       pthread_cond_destroy (_cond);
-      pthread_cond_init (_cond, NULL) ;
+      pthread_cond_init (_cond, os::Linux::condAttr()) ;
     }
     assert_status(status == 0 || status == EINTR ||
                   status == ETIME || status == ETIMEDOUT,
@@ -5726,32 +5765,50 @@ void os::PlatformEvent::unpark() {
 
 static void unpackTime(timespec* absTime, bool isAbsolute, jlong time) {
   assert (time > 0, "convertTime");
+  time_t max_secs = 0;
 
-  struct timeval now;
-  int status = gettimeofday(&now, NULL);
-  assert(status == 0, "gettimeofday");
+  if (!os::Linux::supports_monotonic_clock() || isAbsolute) {
+    struct timeval now;
+    int status = gettimeofday(&now, NULL);
+    assert(status == 0, "gettimeofday");
 
-  time_t max_secs = now.tv_sec + MAX_SECS;
+    max_secs = now.tv_sec + MAX_SECS;
 
-  if (isAbsolute) {
-    jlong secs = time / 1000;
-    if (secs > max_secs) {
-      absTime->tv_sec = max_secs;
-    }
-    else {
-      absTime->tv_sec = secs;
+    if (isAbsolute) {
+      jlong secs = time / 1000;
+      if (secs > max_secs) {
+        absTime->tv_sec = max_secs;
+      } else {
+        absTime->tv_sec = secs;
+      }
+      absTime->tv_nsec = (time % 1000) * NANOSECS_PER_MILLISEC;
+    } else {
+      jlong secs = time / NANOSECS_PER_SEC;
+      if (secs >= MAX_SECS) {
+        absTime->tv_sec = max_secs;
+        absTime->tv_nsec = 0;
+      } else {
+        absTime->tv_sec = now.tv_sec + secs;
+        absTime->tv_nsec = (time % NANOSECS_PER_SEC) + now.tv_usec*1000;
+        if (absTime->tv_nsec >= NANOSECS_PER_SEC) {
+          absTime->tv_nsec -= NANOSECS_PER_SEC;
+          ++absTime->tv_sec; // note: this must be <= max_secs
+        }
+      }
     }
-    absTime->tv_nsec = (time % 1000) * NANOSECS_PER_MILLISEC;
-  }
-  else {
+  } else {
+    // must be relative using monotonic clock
+    struct timespec now;
+    int status = os::Linux::clock_gettime(CLOCK_MONOTONIC, &now);
+    assert_status(status == 0, status, "clock_gettime");
+    max_secs = now.tv_sec + MAX_SECS;
     jlong secs = time / NANOSECS_PER_SEC;
     if (secs >= MAX_SECS) {
       absTime->tv_sec = max_secs;
       absTime->tv_nsec = 0;
-    }
-    else {
+    } else {
       absTime->tv_sec = now.tv_sec + secs;
-      absTime->tv_nsec = (time % NANOSECS_PER_SEC) + now.tv_usec*1000;
+      absTime->tv_nsec = (time % NANOSECS_PER_SEC) + now.tv_nsec;
       if (absTime->tv_nsec >= NANOSECS_PER_SEC) {
         absTime->tv_nsec -= NANOSECS_PER_SEC;
         ++absTime->tv_sec; // note: this must be <= max_secs
@@ -5831,15 +5888,19 @@ void Parker::park(bool isAbsolute, jlong time) {
   jt->set_suspend_equivalent();
   // cleared by handle_special_suspend_equivalent_condition() or java_suspend_self()
 
+  assert(_cur_index == -1, "invariant");
   if (time == 0) {
-    status = pthread_cond_wait (_cond, _mutex) ;
+    _cur_index = REL_INDEX; // arbitrary choice when not timed
+    status = pthread_cond_wait (&_cond[_cur_index], _mutex) ;
   } else {
-    status = os::Linux::safe_cond_timedwait (_cond, _mutex, &absTime) ;
+    _cur_index = isAbsolute ? ABS_INDEX : REL_INDEX;
+    status = os::Linux::safe_cond_timedwait (&_cond[_cur_index], _mutex, &absTime) ;
     if (status != 0 && WorkAroundNPTLTimedWaitHang) {
-      pthread_cond_destroy (_cond) ;
-      pthread_cond_init    (_cond, NULL);
+      pthread_cond_destroy (&_cond[_cur_index]) ;
+      pthread_cond_init    (&_cond[_cur_index], isAbsolute ? NULL : os::Linux::condAttr());
     }
   }
+  _cur_index = -1;
   assert_status(status == 0 || status == EINTR ||
                 status == ETIME || status == ETIMEDOUT,
                 status, "cond_timedwait");
@@ -5868,17 +5929,24 @@ void Parker::unpark() {
   s = _counter;
   _counter = 1;
   if (s < 1) {
-     if (WorkAroundNPTLTimedWaitHang) {
-        status = pthread_cond_signal (_cond) ;
-        assert (status == 0, "invariant") ;
+    // thread might be parked
+    if (_cur_index != -1) {
+      // thread is definitely parked
+      if (WorkAroundNPTLTimedWaitHang) {
+        status = pthread_cond_signal (&_cond[_cur_index]);
+        assert (status == 0, "invariant");
         status = pthread_mutex_unlock(_mutex);
-        assert (status == 0, "invariant") ;
-     } else {
+        assert (status == 0, "invariant");
+      } else {
         status = pthread_mutex_unlock(_mutex);
-        assert (status == 0, "invariant") ;
-        status = pthread_cond_signal (_cond) ;
-        assert (status == 0, "invariant") ;
-     }
+        assert (status == 0, "invariant");
+        status = pthread_cond_signal (&_cond[_cur_index]);
+        assert (status == 0, "invariant");
+      }
+    } else {
+      pthread_mutex_unlock(_mutex);
+      assert (status == 0, "invariant") ;
+    }
   } else {
     pthread_mutex_unlock(_mutex);
     assert (status == 0, "invariant") ;

src/os/linux/vm/os_linux.hpp

@@ -221,6 +221,13 @@ class Linux {
 
   static jlong fast_thread_cpu_time(clockid_t clockid);
 
+  // pthread_cond clock suppport
+  private:
+  static pthread_condattr_t _condattr[1];
+
+  public:
+  static pthread_condattr_t* condAttr() { return _condattr; }
+
   // Stack repair handling
 
   // none present
@@ -295,7 +302,7 @@ class PlatformEvent : public CHeapObj<mtInternal> {
   public:
     PlatformEvent() {
       int status;
-      status = pthread_cond_init (_cond, NULL);
+      status = pthread_cond_init (_cond, os::Linux::condAttr());
       assert_status(status == 0, status, "cond_init");
       status = pthread_mutex_init (_mutex, NULL);
       assert_status(status == 0, status, "mutex_init");
@@ -310,14 +317,19 @@ class PlatformEvent : public CHeapObj<mtInternal> {
     void park () ;
     void unpark () ;
     int  TryPark () ;
-    int  park (jlong millis) ;
+    int  park (jlong millis) ; // relative timed-wait only
     void SetAssociation (Thread * a) { _Assoc = a ; }
 } ;
 
 class PlatformParker : public CHeapObj<mtInternal> {
   protected:
+    enum {
+        REL_INDEX = 0,
+        ABS_INDEX = 1
+    };
+    int _cur_index;  // which cond is in use: -1, 0, 1
     pthread_mutex_t _mutex [1] ;
-    pthread_cond_t  _cond  [1] ;
+    pthread_cond_t  _cond  [2] ; // one for relative times and one for abs.
 
   public:       // TODO-FIXME: make dtor private
     ~PlatformParker() { guarantee (0, "invariant") ; }
@@ -325,10 +337,13 @@ class PlatformParker : public CHeapObj<mtInternal> {
   public:
     PlatformParker() {
       int status;
-      status = pthread_cond_init (_cond, NULL);
-      assert_status(status == 0, status, "cond_init");
+      status = pthread_cond_init (&_cond[REL_INDEX], os::Linux::condAttr());
+      assert_status(status == 0, status, "cond_init rel");
+      status = pthread_cond_init (&_cond[ABS_INDEX], NULL);
+      assert_status(status == 0, status, "cond_init abs");
       status = pthread_mutex_init (_mutex, NULL);
       assert_status(status == 0, status, "mutex_init");
+      _cur_index = -1; // mark as unused
     }
 };