7117303: VM uses non-monotonic time source and complains that it is non-monotonic

Summary: Replaces calls to os::javaTimeMillis(), which does not (and cannot) guarantee monotonicity, in GC code to an equivalent expression that uses os::javaTimeNanos(). os::javaTimeNanos is guaranteed monotonically non-decreasing if the underlying platform provides a monotonic time source. Changes in OS files are to make use of the newly defined constants in globalDefinitions.hpp.
Reviewed-by: dholmes, ysr

src/os/bsd/vm/os_bsd.cpp

@@ -150,7 +150,6 @@
 
 // for timer info max values which include all bits
 #define ALL_64_BITS CONST64(0xFFFFFFFFFFFFFFFF)
-#define SEC_IN_NANOSECS  1000000000LL
 
 #define LARGEPAGES_BIT (1 << 6)
 ////////////////////////////////////////////////////////////////////////////////
@@ -3445,8 +3444,6 @@ size_t os::read(int fd, void *buf, unsigned int nBytes) {
 // generates a SIGUSRx signal. Note that SIGUSR1 can interfere with
 // SIGSEGV, see 4355769.
 
-const int NANOSECS_PER_MILLISECS = 1000000;
-
 int os::sleep(Thread* thread, jlong millis, bool interruptible) {
   assert(thread == Thread::current(),  "thread consistency check");
 
@@ -3469,7 +3466,7 @@ int os::sleep(Thread* thread, jlong millis, bool interruptible) {
         // not a guarantee() because JVM should not abort on kernel/glibc bugs
         assert(!Bsd::supports_monotonic_clock(), "time moving backwards");
       } else {
-        millis -= (newtime - prevtime) / NANOSECS_PER_MILLISECS;
+        millis -= (newtime - prevtime) / NANOSECS_PER_MILLISEC;
       }
 
       if(millis <= 0) {
@@ -3508,7 +3505,7 @@ int os::sleep(Thread* thread, jlong millis, bool interruptible) {
         // not a guarantee() because JVM should not abort on kernel/glibc bugs
         assert(!Bsd::supports_monotonic_clock(), "time moving backwards");
       } else {
-        millis -= (newtime - prevtime) / NANOSECS_PER_MILLISECS;
+        millis -= (newtime - prevtime) / NANOSECS_PER_MILLISEC;
       }
 
       if(millis <= 0) break ;
@@ -4197,7 +4194,7 @@ jlong os::Bsd::fast_thread_cpu_time(clockid_t clockid) {
   int rc = os::Bsd::clock_gettime(clockid, &tp);
   assert(rc == 0, "clock_gettime is expected to return 0 code");
 
-  return (tp.tv_sec * SEC_IN_NANOSECS) + tp.tv_nsec;
+  return (tp.tv_sec * NANOSECS_PER_SEC) + tp.tv_nsec;
 }
 #endif
 
@@ -5522,9 +5519,6 @@ void os::PlatformEvent::unpark() {
  * is no need to track notifications.
  */
 
-
-#define NANOSECS_PER_SEC 1000000000
-#define NANOSECS_PER_MILLISEC 1000000
 #define MAX_SECS 100000000
 /*
  * This code is common to bsd and solaris and will be moved to a

src/os/linux/vm/os_linux.cpp

@@ -127,7 +127,6 @@
 
 // for timer info max values which include all bits
 #define ALL_64_BITS CONST64(0xFFFFFFFFFFFFFFFF)
-#define SEC_IN_NANOSECS  1000000000LL
 
 #define LARGEPAGES_BIT (1 << 6)
 ////////////////////////////////////////////////////////////////////////////////
@@ -3259,8 +3258,6 @@ size_t os::read(int fd, void *buf, unsigned int nBytes) {
 // generates a SIGUSRx signal. Note that SIGUSR1 can interfere with
 // SIGSEGV, see 4355769.
 
-const int NANOSECS_PER_MILLISECS = 1000000;
-
 int os::sleep(Thread* thread, jlong millis, bool interruptible) {
   assert(thread == Thread::current(),  "thread consistency check");
 
@@ -3283,7 +3280,7 @@ int os::sleep(Thread* thread, jlong millis, bool interruptible) {
         // not a guarantee() because JVM should not abort on kernel/glibc bugs
         assert(!Linux::supports_monotonic_clock(), "time moving backwards");
       } else {
-        millis -= (newtime - prevtime) / NANOSECS_PER_MILLISECS;
+        millis -= (newtime - prevtime) / NANOSECS_PER_MILLISEC;
       }
 
       if(millis <= 0) {
@@ -3322,7 +3319,7 @@ int os::sleep(Thread* thread, jlong millis, bool interruptible) {
         // not a guarantee() because JVM should not abort on kernel/glibc bugs
         assert(!Linux::supports_monotonic_clock(), "time moving backwards");
       } else {
-        millis -= (newtime - prevtime) / NANOSECS_PER_MILLISECS;
+        millis -= (newtime - prevtime) / NANOSECS_PER_MILLISEC;
       }
 
       if(millis <= 0) break ;
@@ -3924,7 +3921,7 @@ jlong os::Linux::fast_thread_cpu_time(clockid_t clockid) {
   int rc = os::Linux::clock_gettime(clockid, &tp);
   assert(rc == 0, "clock_gettime is expected to return 0 code");
 
-  return (tp.tv_sec * SEC_IN_NANOSECS) + tp.tv_nsec;
+  return (tp.tv_sec * NANOSECS_PER_SEC) + tp.tv_nsec;
 }
 
 /////
@@ -5165,9 +5162,6 @@ void os::PlatformEvent::unpark() {
  * is no need to track notifications.
  */
 
-
-#define NANOSECS_PER_SEC 1000000000
-#define NANOSECS_PER_MILLISEC 1000000
 #define MAX_SECS 100000000
 /*
  * This code is common to linux and solaris and will be moved to a

src/os/solaris/vm/os_solaris.cpp

@@ -1674,7 +1674,6 @@ void* os::thread_local_storage_at(int index) {
 }
 
 
-const int NANOSECS_PER_MILLISECS = 1000000;
 // gethrtime can move backwards if read from one cpu and then a different cpu
 // getTimeNanos is guaranteed to not move backward on Solaris
 // local spinloop created as faster for a CAS on an int than
@@ -1803,7 +1802,7 @@ double os::elapsedVTime() {
 // getTimeMillis guaranteed to not move backwards on Solaris
 jlong getTimeMillis() {
   jlong nanotime = getTimeNanos();
-  return (jlong)(nanotime / NANOSECS_PER_MILLISECS);
+  return (jlong)(nanotime / NANOSECS_PER_MILLISEC);
 }
 
 // Must return millis since Jan 1 1970 for JVM_CurrentTimeMillis
@@ -6064,10 +6063,7 @@ void os::PlatformEvent::unpark() {
  * is no need to track notifications.
  */
 
-#define NANOSECS_PER_SEC 1000000000
-#define NANOSECS_PER_MILLISEC 1000000
 #define MAX_SECS 100000000
-
 /*
  * This code is common to linux and solaris and will be moved to a
  * common place in dolphin.

src/os/windows/vm/os_windows.cpp

@@ -821,17 +821,15 @@ jlong os::javaTimeMillis() {
   }
 }
 
-#define NANOS_PER_SEC         CONST64(1000000000)
-#define NANOS_PER_MILLISEC    1000000
 jlong os::javaTimeNanos() {
   if (!has_performance_count) {
-    return javaTimeMillis() * NANOS_PER_MILLISEC; // the best we can do.
+    return javaTimeMillis() * NANOSECS_PER_MILLISEC; // the best we can do.
   } else {
     LARGE_INTEGER current_count;
     QueryPerformanceCounter(&current_count);
     double current = as_long(current_count);
     double freq = performance_frequency;
-    jlong time = (jlong)((current/freq) * NANOS_PER_SEC);
+    jlong time = (jlong)((current/freq) * NANOSECS_PER_SEC);
     return time;
   }
 }
@@ -847,15 +845,15 @@ void os::javaTimeNanos_info(jvmtiTimerInfo *info_ptr) {
     info_ptr->may_skip_forward = true;
   } else {
     jlong freq = performance_frequency;
-    if (freq < NANOS_PER_SEC) {
+    if (freq < NANOSECS_PER_SEC) {
       // the performance counter is 64 bits and we will
       // be multiplying it -- so no wrap in 64 bits
       info_ptr->max_value = ALL_64_BITS;
-    } else if (freq > NANOS_PER_SEC) {
+    } else if (freq > NANOSECS_PER_SEC) {
       // use the max value the counter can reach to
       // determine the max value which could be returned
       julong max_counter = (julong)ALL_64_BITS;
-      info_ptr->max_value = (jlong)(max_counter / (freq / NANOS_PER_SEC));
+      info_ptr->max_value = (jlong)(max_counter / (freq / NANOSECS_PER_SEC));
     } else {
       // the performance counter is 64 bits and we will
       // be using it directly -- so no wrap in 64 bits

src/share/vm/gc_implementation/parallelScavenge/psMarkSweep.cpp

@@ -672,15 +672,20 @@ void PSMarkSweep::mark_sweep_phase4() {
 }
 
 jlong PSMarkSweep::millis_since_last_gc() {
-  jlong ret_val = os::javaTimeMillis() - _time_of_last_gc;
+  // We need a monotonically non-deccreasing time in ms but
+  // os::javaTimeMillis() does not guarantee monotonicity.
+  jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
+  jlong ret_val = now - _time_of_last_gc;
   // XXX See note in genCollectedHeap::millis_since_last_gc().
   if (ret_val < 0) {
-    NOT_PRODUCT(warning("time warp: %d", ret_val);)
+    NOT_PRODUCT(warning("time warp: "INT64_FORMAT, ret_val);)
     return 0;
   }
   return ret_val;
 }
 
 void PSMarkSweep::reset_millis_since_last_gc() {
-  _time_of_last_gc = os::javaTimeMillis();
+  // We need a monotonically non-deccreasing time in ms but
+  // os::javaTimeMillis() does not guarantee monotonicity.
+  _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 }

src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.cpp

@@ -3398,17 +3398,22 @@ PSParallelCompact::move_and_update(ParCompactionManager* cm, SpaceId space_id) {
 }
 
 jlong PSParallelCompact::millis_since_last_gc() {
-  jlong ret_val = os::javaTimeMillis() - _time_of_last_gc;
+  // We need a monotonically non-deccreasing time in ms but
+  // os::javaTimeMillis() does not guarantee monotonicity.
+  jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
+  jlong ret_val = now - _time_of_last_gc;
   // XXX See note in genCollectedHeap::millis_since_last_gc().
   if (ret_val < 0) {
-    NOT_PRODUCT(warning("time warp: %d", ret_val);)
+    NOT_PRODUCT(warning("time warp: "INT64_FORMAT, ret_val);)
     return 0;
   }
   return ret_val;
 }
 
 void PSParallelCompact::reset_millis_since_last_gc() {
-  _time_of_last_gc = os::javaTimeMillis();
+  // We need a monotonically non-deccreasing time in ms but
+  // os::javaTimeMillis() does not guarantee monotonicity.
+  _time_of_last_gc = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 }
 
 ParMarkBitMap::IterationStatus MoveAndUpdateClosure::copy_until_full()

src/share/vm/memory/genCollectedHeap.cpp

@@ -1460,26 +1460,22 @@ class GenTimeOfLastGCClosure: public GenCollectedHeap::GenClosure {
 };
 
 jlong GenCollectedHeap::millis_since_last_gc() {
-  jlong now = os::javaTimeMillis();
+  // We need a monotonically non-deccreasing time in ms but
+  // os::javaTimeMillis() does not guarantee monotonicity.
+  jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
   GenTimeOfLastGCClosure tolgc_cl(now);
   // iterate over generations getting the oldest
   // time that a generation was collected
   generation_iterate(&tolgc_cl, false);
   tolgc_cl.do_generation(perm_gen());
-  // XXX Despite the assert above, since javaTimeMillis()
-  // doesnot guarantee monotonically increasing return
-  // values (note, i didn't say "strictly monotonic"),
-  // we need to guard against getting back a time
-  // later than now. This should be fixed by basing
-  // on someting like gethrtime() which guarantees
-  // monotonicity. Note that cond_wait() is susceptible
-  // to a similar problem, because its interface is
-  // based on absolute time in the form of the
-  // system time's notion of UCT. See also 4506635
-  // for yet another problem of similar nature. XXX
+
+  // javaTimeNanos() is guaranteed to be monotonically non-decreasing
+  // provided the underlying platform provides such a time source
+  // (and it is bug free). So we still have to guard against getting
+  // back a time later than 'now'.
   jlong retVal = now - tolgc_cl.time();
   if (retVal < 0) {
-    NOT_PRODUCT(warning("time warp: %d", retVal);)
+    NOT_PRODUCT(warning("time warp: "INT64_FORMAT, retVal);)
     return 0;
   }
   return retVal;

src/share/vm/memory/generation.hpp

@@ -413,10 +413,13 @@ class Generation: public CHeapObj {
   // Time (in ms) when we were last collected or now if a collection is
   // in progress.
   virtual jlong time_of_last_gc(jlong now) {
-    // XXX See note in genCollectedHeap::millis_since_last_gc()
+    // Both _time_of_last_gc and now are set using a time source
+    // that guarantees monotonically non-decreasing values provided
+    // the underlying platform provides such a source. So we still
+    // have to guard against non-monotonicity.
     NOT_PRODUCT(
       if (now < _time_of_last_gc) {
-        warning("time warp: %d to %d", _time_of_last_gc, now);
+        warning("time warp: "INT64_FORMAT" to "INT64_FORMAT, _time_of_last_gc, now);
       }
     )
     return _time_of_last_gc;

src/share/vm/memory/referenceProcessor.cpp

@@ -43,7 +43,9 @@ void referenceProcessor_init() {
 }
 
 void ReferenceProcessor::init_statics() {
-  jlong now = os::javaTimeMillis();
+  // We need a monotonically non-deccreasing time in ms but
+  // os::javaTimeMillis() does not guarantee monotonicity.
+  jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 
   // Initialize the soft ref timestamp clock.
   _soft_ref_timestamp_clock = now;
@@ -151,7 +153,10 @@ void ReferenceProcessor::weak_oops_do(OopClosure* f) {
 void ReferenceProcessor::update_soft_ref_master_clock() {
   // Update (advance) the soft ref master clock field. This must be done
   // after processing the soft ref list.
-  jlong now = os::javaTimeMillis();
+
+  // We need a monotonically non-deccreasing time in ms but
+  // os::javaTimeMillis() does not guarantee monotonicity.
+  jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
   jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
   assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
 
@@ -161,10 +166,11 @@ void ReferenceProcessor::update_soft_ref_master_clock() {
             _soft_ref_timestamp_clock, now);
   }
   )
-  // In product mode, protect ourselves from system time being adjusted
-  // externally and going backward; see note in the implementation of
-  // GenCollectedHeap::time_since_last_gc() for the right way to fix
-  // this uniformly throughout the VM; see bug-id 4741166. XXX
+  // The values of now and _soft_ref_timestamp_clock are set using
+  // javaTimeNanos(), which is guaranteed to be monotonically
+  // non-decreasing provided the underlying platform provides such
+  // a time source (and it is bug free).
+  // In product mode, however, protect ourselves from non-monotonicty.
   if (now > _soft_ref_timestamp_clock) {
     _soft_ref_timestamp_clock = now;
     java_lang_ref_SoftReference::set_clock(now);

src/share/vm/utilities/globalDefinitions.hpp

@@ -175,6 +175,9 @@ const int MILLIUNITS    = 1000;         // milli units per base unit
 const int MICROUNITS    = 1000000;      // micro units per base unit
 const int NANOUNITS     = 1000000000;   // nano units per base unit
 
+const jlong NANOSECS_PER_SEC      = CONST64(1000000000);
+const jint  NANOSECS_PER_MILLISEC = 1000000;
+
 inline const char* proper_unit_for_byte_size(size_t s) {
   if (s >= 10*M) {
     return "M";