changeset 11354:d6a5cbeb8198

8068730: Increase the precision of the implementation of java.time.Clock.systemUTC() Summary: Changes the implementation of java.time.Clock.systemUTC() to take advantage of the maximum resolution of the underlying native clock on which System.currentTimeMillis() is based. Reviewed-by: dholmes, rriggs, scolebourne, sla
author dfuchs
date Wed, 28 Jan 2015 17:48:59 +0100
parents 7405b7071ba0
children 97b8292cdd51
files src/java.base/share/classes/java/time/Clock.java src/java.base/share/classes/java/util/Formatter.java src/java.base/share/classes/sun/misc/VM.java src/java.base/share/native/include/jvm.h src/java.base/share/native/libjava/VM.c test/java/time/tck/java/time/TCKLocalDateTime.java test/java/time/tck/java/time/TCKLocalTime.java test/java/time/tck/java/time/TCKZonedDateTime.java test/java/time/test/java/time/TestClock_System.java test/java/time/test/java/util/TestFormatter.java test/sun/misc/VM/GetNanoTimeAdjustment.java
diffstat 11 files changed, 714 insertions(+), 15 deletions(-) [+]
line wrap: on
line diff
--- a/src/java.base/share/classes/java/time/Clock.java	Wed Jan 28 09:23:41 2015 +0100
+++ b/src/java.base/share/classes/java/time/Clock.java	Wed Jan 28 17:48:59 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -61,12 +61,15 @@
  */
 package java.time;
 
+import java.io.IOException;
+import java.io.ObjectInputStream;
 import static java.time.LocalTime.NANOS_PER_MINUTE;
 import static java.time.LocalTime.NANOS_PER_SECOND;
 
 import java.io.Serializable;
 import java.util.Objects;
 import java.util.TimeZone;
+import sun.misc.VM;
 
 /**
  * A clock providing access to the current instant, date and time using a time-zone.
@@ -446,10 +449,22 @@
      */
     static final class SystemClock extends Clock implements Serializable {
         private static final long serialVersionUID = 6740630888130243051L;
+        private static final long OFFSET_SEED =
+                System.currentTimeMillis()/1000 - 1024; // initial offest
         private final ZoneId zone;
+        // We don't actually need a volatile here.
+        // We don't care if offset is set or read concurrently by multiple
+        // threads - we just need a value which is 'recent enough' - in other
+        // words something that has been updated at least once in the last
+        // 2^32 secs (~136 years). And even if we by chance see an invalid
+        // offset, the worst that can happen is that we will get a -1 value
+        // from getNanoTimeAdjustment, forcing us to update the offset
+        // once again.
+        private transient long offset;
 
         SystemClock(ZoneId zone) {
             this.zone = zone;
+            this.offset = OFFSET_SEED;
         }
         @Override
         public ZoneId getZone() {
@@ -464,11 +479,50 @@
         }
         @Override
         public long millis() {
+            // System.currentTimeMillis() and VM.getNanoTimeAdjustment(offset)
+            // use the same time source - System.currentTimeMillis() simply
+            // limits the resolution to milliseconds.
+            // So we take the faster path and call System.currentTimeMillis()
+            // directly - in order to avoid the performance penalty of
+            // VM.getNanoTimeAdjustment(offset) which is less efficient.
             return System.currentTimeMillis();
         }
         @Override
         public Instant instant() {
-            return Instant.ofEpochMilli(millis());
+            // Take a local copy of offset. offset can be updated concurrently
+            // by other threads (even if we haven't made it volatile) so we will
+            // work with a local copy.
+            long localOffset = offset;
+            long adjustment = VM.getNanoTimeAdjustment(localOffset);
+
+            if (adjustment == -1) {
+                // -1 is a sentinel value returned by VM.getNanoTimeAdjustment
+                // when the offset it is given is too far off the current UTC
+                // time. In principle, this should not happen unless the
+                // JVM has run for more than ~136 years (not likely) or
+                // someone is fiddling with the system time, or the offset is
+                // by chance at 1ns in the future (very unlikely).
+                // We can easily recover from all these conditions by bringing
+                // back the offset in range and retry.
+
+                // bring back the offset in range. We use -1024 to make
+                // it more unlikely to hit the 1ns in the future condition.
+                localOffset = System.currentTimeMillis()/1000 - 1024;
+
+                // retry
+                adjustment = VM.getNanoTimeAdjustment(localOffset);
+
+                if (adjustment == -1) {
+                    // Should not happen: we just recomputed a new offset.
+                    // It should have fixed the issue.
+                    throw new InternalError("Offset " + localOffset + " is not in range");
+                } else {
+                    // OK - recovery succeeded. Update the offset for the
+                    // next call...
+                    offset = localOffset;
+                }
+            }
+            return Instant.ofEpochSecond(localOffset, adjustment);
         }
         @Override
         public boolean equals(Object obj) {
@@ -485,6 +539,12 @@
         public String toString() {
             return "SystemClock[" + zone + "]";
         }
+        private void readObject(ObjectInputStream is)
+                throws IOException, ClassNotFoundException {
+            // ensure that offset is initialized
+            is.defaultReadObject();
+            offset = OFFSET_SEED;
+        }
     }
 
     //-----------------------------------------------------------------------
--- a/src/java.base/share/classes/java/util/Formatter.java	Wed Jan 28 09:23:41 2015 +0100
+++ b/src/java.base/share/classes/java/util/Formatter.java	Wed Jan 28 17:48:59 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -57,6 +57,7 @@
 import java.time.temporal.ChronoField;
 import java.time.temporal.TemporalAccessor;
 import java.time.temporal.TemporalQueries;
+import java.time.temporal.UnsupportedTemporalTypeException;
 
 import sun.misc.DoubleConsts;
 import sun.misc.FormattedFloatingDecimal;
@@ -4056,7 +4057,12 @@
                     break;
                 }
                 case DateTime.NANOSECOND:  { // 'N' (000000000 - 999999999)
-                    int i = t.get(ChronoField.MILLI_OF_SECOND) * 1000000;
+                    int i;
+                    try {
+                        i = t.get(ChronoField.NANO_OF_SECOND);
+                    } catch (UnsupportedTemporalTypeException u) {
+                        i = t.get(ChronoField.MILLI_OF_SECOND) * 1000000;
+                    }
                     Flags flags = Flags.ZERO_PAD;
                     sb.append(localizedMagnitude(null, i, flags, 9, l));
                     break;
--- a/src/java.base/share/classes/sun/misc/VM.java	Wed Jan 28 09:23:41 2015 +0100
+++ b/src/java.base/share/classes/sun/misc/VM.java	Wed Jan 28 17:48:59 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1996, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -402,6 +402,36 @@
      */
     public static native long getegid();
 
+    /**
+     * Get a nanosecond time stamp adjustment in the form of a single long.
+     *
+     * This value can be used to create an instant using
+     * {@link java.time.Instant#ofEpochSecond(long, long)
+     *  java.time.Instant.ofEpochSecond(offsetInSeconds,
+     *  getNanoTimeAdjustment(offsetInSeconds))}.
+     * <p>
+     * The value returned has the best resolution available to the JVM on
+     * the current system.
+     * This is usually down to microseconds - or tenth of microseconds -
+     * depending on the OS/Hardware and the JVM implementation.
+     *
+     * @param offsetInSeconds The offset in seconds from which the nanosecond
+     *        time stamp should be computed.
+     *
+     * @apiNote The offset should be recent enough - so that
+     *         {@code offsetInSeconds} is within {@code +/- 2^32} seconds of the
+     *         current UTC time. If the offset is too far off, {@code -1} will be
+     *         returned. As such, {@code -1} must not be considered as a valid
+     *         nano time adjustment, but as an exception value indicating
+     *         that an offset closer to the current time should be used.
+     *
+     * @return A nanosecond time stamp adjustment in the form of a single long.
+     *     If the offset is too far off the current time, this method returns -1.
+     *     In that case, the caller should call this method again, passing a
+     *     more accurate offset.
+     */
+    public static native long getNanoTimeAdjustment(long offsetInSeconds);
+
     static {
         initialize();
     }
--- a/src/java.base/share/native/include/jvm.h	Wed Jan 28 09:23:41 2015 +0100
+++ b/src/java.base/share/native/include/jvm.h	Wed Jan 28 17:48:59 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -104,6 +104,9 @@
 JNIEXPORT jlong JNICALL
 JVM_NanoTime(JNIEnv *env, jclass ignored);
 
+JNIEXPORT jlong JNICALL
+JVM_GetNanoTimeAdjustment(JNIEnv *env, jclass ignored, jlong offset_secs);
+
 JNIEXPORT void JNICALL
 JVM_ArrayCopy(JNIEnv *env, jclass ignored, jobject src, jint src_pos,
               jobject dst, jint dst_pos, jint length);
--- a/src/java.base/share/native/libjava/VM.c	Wed Jan 28 09:23:41 2015 +0100
+++ b/src/java.base/share/native/libjava/VM.c	Wed Jan 28 17:48:59 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2004, 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2004, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -33,6 +33,11 @@
 
 #include "sun_misc_VM.h"
 
+/* Only register the performance-critical methods */
+static JNINativeMethod methods[] = {
+    {"getNanoTimeAdjustment", "(J)J", (void *)&JVM_GetNanoTimeAdjustment}
+};
+
 JNIEXPORT jobject JNICALL
 Java_sun_misc_VM_latestUserDefinedLoader(JNIEnv *env, jclass cls) {
     return JVM_LatestUserDefinedLoader(env);
@@ -49,6 +54,14 @@
         return;
     }
 
+    // Registers implementations of native methods described in methods[]
+    // above.
+    // In particular, registers JVM_GetNanoTimeAdjustment as the implementation
+    // of the native sun.misc.VM.getNanoTimeAdjustment - avoiding the cost of
+    // introducing a Java_sun_misc_VM_getNanoTimeAdjustment  wrapper
+    (*env)->RegisterNatives(env, cls,
+                            methods, sizeof(methods)/sizeof(methods[0]));
+
     func_p = (GetJvmVersionInfo_fp) JDK_FindJvmEntry("JVM_GetVersionInfo");
      if (func_p != NULL) {
         jvm_version_info info;
--- a/test/java/time/tck/java/time/TCKLocalDateTime.java	Wed Jan 28 09:23:41 2015 +0100
+++ b/test/java/time/tck/java/time/TCKLocalDateTime.java	Wed Jan 28 17:48:59 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -292,7 +292,8 @@
             expected = LocalDateTime.now(Clock.system(zone));
             test = LocalDateTime.now(zone);
         }
-        assertEquals(test, expected);
+        assertEquals(test.truncatedTo(ChronoUnit.SECONDS),
+                     expected.truncatedTo(ChronoUnit.SECONDS));
     }
 
     //-----------------------------------------------------------------------
--- a/test/java/time/tck/java/time/TCKLocalTime.java	Wed Jan 28 09:23:41 2015 +0100
+++ b/test/java/time/tck/java/time/TCKLocalTime.java	Wed Jan 28 17:48:59 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -246,7 +246,8 @@
             expected = LocalTime.now(Clock.system(zone));
             test = LocalTime.now(zone);
         }
-        assertEquals(test, expected);
+        assertEquals(test.truncatedTo(ChronoUnit.SECONDS),
+                     expected.truncatedTo(ChronoUnit.SECONDS));
     }
 
     //-----------------------------------------------------------------------
--- a/test/java/time/tck/java/time/TCKZonedDateTime.java	Wed Jan 28 09:23:41 2015 +0100
+++ b/test/java/time/tck/java/time/TCKZonedDateTime.java	Wed Jan 28 17:48:59 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -260,7 +260,8 @@
             expected = ZonedDateTime.now(Clock.system(zone));
             test = ZonedDateTime.now(zone);
         }
-        assertEquals(test, expected);
+        assertEquals(test.truncatedTo(ChronoUnit.SECONDS),
+                     expected.truncatedTo(ChronoUnit.SECONDS));
     }
 
     //-----------------------------------------------------------------------
--- a/test/java/time/test/java/time/TestClock_System.java	Wed Jan 28 09:23:41 2015 +0100
+++ b/test/java/time/test/java/time/TestClock_System.java	Wed Jan 28 17:48:59 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -62,7 +62,9 @@
 import static org.testng.Assert.assertEquals;
 import static org.testng.Assert.assertSame;
 
+import java.lang.reflect.Field;
 import java.time.Clock;
+import java.time.Instant;
 import java.time.ZoneId;
 
 import org.testng.annotations.Test;
@@ -87,4 +89,298 @@
         assertEquals(test.toString(), "SystemClock[Europe/Paris]");
     }
 
+    //-----------------------------------------------------------------------
+
+    private static String formatTime(String prefix, Instant time) {
+        return prefix + ": " + time + " - seconds: "
+                        + time.getEpochSecond() + ", nanos: "
+                        + time.getNano();
+    }
+
+    public void test_ClockResolution() {
+        Clock highestUTC = Clock.systemUTC();
+
+        Instant start = Instant.ofEpochMilli(System.currentTimeMillis());
+
+        try {
+            // smoke test
+            Instant system1 = Instant.ofEpochMilli(System.currentTimeMillis());
+            Instant system2 = Instant.ofEpochMilli(System.currentTimeMillis());
+            Instant highest1 = highestUTC.instant();
+            Instant highest2 = highestUTC.instant();
+            System.out.println(formatTime("\nsystemUTC #1            ", system1));
+            System.out.println(formatTime("systemUTC #2            ", system2));
+            System.out.println(formatTime("highestResolutionUTC #1 ", highest1));
+            System.out.println(formatTime("highestResolutionUTC #2 ", highest2));
+
+            if (system2.isBefore(system1)) {
+                System.err.println("system2 is before system1!");
+                System.err.println(formatTime("\n\tsystem1", system1));
+                System.err.println(formatTime("\n\tsystem2", system2));
+                throw new RuntimeException("system2 is before system1!"
+                        + formatTime("\n\tsystem1", system1)
+                        + formatTime("\n\tsystem2", system2));
+            }
+            if (highest2.isBefore(highest1)) {
+                System.err.println("highest2 is before highest1!");
+                System.err.println(formatTime("\n\thighest1", system1));
+                System.err.println(formatTime("\n\tsystem2", highest2));
+                throw new RuntimeException("highest2 is before system1!"
+                        + formatTime("\n\thighest1", system1)
+                        + formatTime("\n\tsystem2", highest2));
+            }
+
+            // better test - but depends on implementation details.
+            // we're not rounding - so highest1 should be greater or equal to
+            // system1
+            system1 = Instant.ofEpochMilli(System.currentTimeMillis());
+            highest1 = highestUTC.instant();
+
+            System.out.println(formatTime("\nsystemUTC            ", system1));
+            System.out.println(formatTime("highestResolutionUTC ", highest1));
+
+            if (highest1.isBefore(system1)) {
+                System.err.println("highest1 is before system1!");
+                System.err.println(formatTime("\n\tsystem1", system1));
+                System.err.println(formatTime("\n\thighest1", highest1));
+                throw new RuntimeException("highest1 is before system1!"
+                        + formatTime("\n\tsystem1", system1)
+                        + formatTime("\n\thighest1", highest1));
+            }
+
+            int count=0;
+            // let's preheat the system a bit:
+            for (int i = 0; i < 1000 ; i++) {
+                system1 = Instant.ofEpochMilli(System.currentTimeMillis());
+                highest1 = highestUTC.instant();
+                final int sysnan = system1.getNano();
+                final int nanos = highest1.getNano();
+                if ((nanos % 1000000) > 0) {
+                    count++; // we have micro seconds
+                }
+                if ((sysnan % 1000000) > 0) {
+                    throw new RuntimeException("Expected only millisecconds "
+                            + "precision for systemUTC, found "
+                            + (sysnan % 1000000) + " remainder.");
+                }
+            }
+            System.out.println("\nNumber of time stamps which had better than"
+                    + " millisecond precision: "+count+"/"+1000);
+            System.out.println(formatTime("\nsystemUTC            ", system1));
+            System.out.println(formatTime("highestResolutionUTC ", highest1));
+            if (count == 0) {
+                System.err.println("Something is strange: no microsecond "
+                        + "precision with highestResolutionUTC?");
+                throw new RuntimeException("Micro second preccision not reached");
+            }
+
+            // check again
+            if (highest1.isBefore(system1)) {
+                System.err.println("highest1 is before system1!");
+                System.err.println(formatTime("\n\tsystem1", system1));
+                System.err.println(formatTime("\n\thighest1", highest1));
+                throw new RuntimeException("highest1 is before system1!"
+                        + formatTime("\n\tsystem1", system1)
+                        + formatTime("\n\thighest1", highest1));
+            }
+
+            // leap of faith: ensure that highest1 is from within 10 secs of
+            //   system1
+            if (highest1.toEpochMilli() != system1.toEpochMilli()) {
+                long delta = highest1.getEpochSecond() - system1.getEpochSecond();
+                if (delta > 10) {
+                    throw new RuntimeException("Unexpected long delay between two clocks ("
+                            + delta + " seconds)"
+                            + formatTime("\n\t system1", system1)
+                            + formatTime("\n\t highest1", highest1));
+
+                }
+            } else {
+                System.out.println("You won the lottery: the two dates are within 1 millisecond!\n");
+            }
+
+        } finally {
+            Instant stop = Instant.ofEpochMilli(System.currentTimeMillis());
+            if (start.isAfter(stop)) {
+                // This should not happen - but can (un)probably be observed
+                // when switching to summer time, or if another application
+                // is switching the system date...
+                System.err.println("Cannot test - date was setback: "
+                        + formatTime("\n\tstarted at", start)
+                        + formatTime("\n\tstopped at", stop) + "\n");
+                return; // will prevent exceptions from being propagated.
+            }
+        }
+    }
+
+    static final long MAX_OFFSET = 0x0100000000L;
+    static final long MIN_OFFSET = -MAX_OFFSET;
+
+    // A helper class to test that SystemClock correctly recomputes
+    // its offset.
+    static class SystemClockOffset {
+
+        static final int MILLIS_IN_SECOND = 1000;
+        static final int NANOS_IN_MILLI = 1000_000;
+        static final int NANOS_IN_MICRO = 1000;
+        static final int NANOS_IN_SECOND = 1000_000_000;
+
+        static final boolean verbose = true;
+        static final Clock systemUTC = Clock.systemUTC();
+        static final Field offsetField;
+
+        static {
+            try {
+                offsetField = Class.forName("java.time.Clock$SystemClock").getDeclaredField("offset");
+                offsetField.setAccessible(true);
+            } catch (ClassNotFoundException | NoSuchFieldException ex) {
+                throw new ExceptionInInitializerError(ex);
+            }
+        }
+
+        static enum Answer {
+
+            YES, // isOffLimit = YES:   we must get -1
+            NO, // isOffLimit = NO:    we must not not get -1
+            MAYBE  // isOffLimit = MAYBE: we might get -1 or a valid adjustment.
+        };
+
+        static long distance(long one, long two) {
+            return one > two ? Math.subtractExact(one, two)
+                    : Math.subtractExact(two, one);
+        }
+
+        static Answer isOffLimits(long before, long after, long offset) {
+            long relativeDistanceBefore = distance(before, offset);
+            long relativeDistanceAfter = distance(after, offset);
+            if (relativeDistanceBefore >= MAX_OFFSET && relativeDistanceAfter >= MAX_OFFSET) {
+                return Answer.YES;
+            }
+            if (relativeDistanceBefore < MAX_OFFSET && relativeDistanceAfter < MAX_OFFSET) {
+                if (relativeDistanceBefore == 0 || relativeDistanceAfter == 0) {
+                    return Answer.MAYBE; // unlucky case where
+                }
+                return Answer.NO;
+            }
+            return Answer.MAYBE;
+        }
+
+        static void testWithOffset(String name, long offset)
+                throws IllegalAccessException {
+            testWithOffset(name, offset, systemUTC);
+        }
+
+        static void testWithOffset(String name, long offset, Clock clock)
+                throws IllegalAccessException {
+            offsetField.set(clock, offset);
+            long beforeMillis = System.currentTimeMillis();
+            final Instant instant = clock.instant();
+            long afterMillis = System.currentTimeMillis();
+            long actualOffset = offsetField.getLong(clock);
+            long instantMillis = instant.getEpochSecond() * MILLIS_IN_SECOND
+                    + instant.getNano() / NANOS_IN_MILLI;
+            if (instantMillis < beforeMillis || instantMillis > afterMillis) {
+                throw new RuntimeException(name
+                        + ": Invalid instant: " + instant
+                        + " (~" + instantMillis + "ms)"
+                        + " when time in millis is in ["
+                        + beforeMillis + ", " + afterMillis
+                        + "] and offset in seconds is " + offset);
+            }
+            Answer isOffLimits = isOffLimits(beforeMillis / MILLIS_IN_SECOND,
+                    afterMillis / MILLIS_IN_SECOND, offset);
+            switch (isOffLimits) {
+                case YES:
+                    if (actualOffset == offset) {
+                        throw new RuntimeException(name
+                                + ": offset was offlimit but was not recomputed "
+                                + " when time in millis is in ["
+                                + beforeMillis + ", " + afterMillis
+                                + "] and offset in seconds was " + offset);
+                    }
+                    break;
+                case NO:
+                    if (actualOffset != offset) {
+                        throw new RuntimeException(name
+                                + ": offset was not offlimit but was recomputed.");
+                    }
+                    break;
+                default:
+                    break;
+            }
+            if (distance(actualOffset, instant.getEpochSecond()) >= MAX_OFFSET) {
+                throw new RuntimeException(name + ": Actual offset is too far off:"
+                        + " offset=" + actualOffset
+                        + "instant.seconds=" + instant.getEpochSecond());
+            }
+            long adjustment = (instant.getEpochSecond() - actualOffset) * NANOS_IN_SECOND
+                    + instant.getNano();
+            validateAdjustment(name, actualOffset, beforeMillis, afterMillis, adjustment);
+        }
+
+        static void validateAdjustment(String name, long offset, long beforeMillis,
+                long afterMillis, long adjustment) {
+            System.out.println("Validating adjustment: " + adjustment);
+            long expectedMax = distance(offset, beforeMillis / MILLIS_IN_SECOND)
+                    * NANOS_IN_SECOND
+                    + (beforeMillis % MILLIS_IN_SECOND) * NANOS_IN_MILLI
+                    + (afterMillis - beforeMillis + 1) * NANOS_IN_MILLI;
+            long absoluteAdjustment = distance(0, adjustment);
+            if (absoluteAdjustment > expectedMax) {
+                long adjSec = absoluteAdjustment / NANOS_IN_SECOND;
+                long adjMil = (absoluteAdjustment % NANOS_IN_SECOND) / NANOS_IN_MILLI;
+                long adjMic = (absoluteAdjustment % NANOS_IN_MILLI) / NANOS_IN_MICRO;
+                long adjNan = (absoluteAdjustment % NANOS_IN_MICRO);
+                long expSec = expectedMax / NANOS_IN_SECOND;
+                long expMil = (expectedMax % NANOS_IN_SECOND) / NANOS_IN_MILLI;
+                long expMic = (expectedMax % NANOS_IN_MILLI) / NANOS_IN_MICRO;
+                long expNan = (expectedMax % NANOS_IN_MICRO);
+                System.err.println("Excessive adjustment: " + adjSec + "s, "
+                        + adjMil + "ms, " + adjMic + "mics, " + adjNan + "ns");
+                System.err.println("Epected max: " + expSec + "s, "
+                        + expMil + "ms, " + expMic + "mics, " + expNan + "ns");
+
+                throw new RuntimeException(name
+                        + ": Excessive adjustment: " + adjustment
+                        + " when time in millis is in ["
+                        + beforeMillis + ", " + afterMillis
+                        + "] and offset in seconds is " + offset);
+            }
+        }
+    }
+
+    public void test_OffsetRegular() throws IllegalAccessException {
+        System.out.println("*** Testing regular cases ***");
+        SystemClockOffset.testWithOffset("System.currentTimeMillis()/1000",
+                System.currentTimeMillis()/1000);
+        SystemClockOffset.testWithOffset("System.currentTimeMillis()/1000 - 1024",
+                System.currentTimeMillis()/1000 - 1024);
+        SystemClockOffset.testWithOffset("System.currentTimeMillis()/1000 + 1024",
+                System.currentTimeMillis()/1000 + 1024);
+    }
+
+    public void test_OffsetLimits() throws IllegalAccessException {
+        System.out.println("*** Testing limits ***");
+        SystemClockOffset.testWithOffset("System.currentTimeMillis()/1000 - MAX_OFFSET + 1",
+                System.currentTimeMillis()/1000 - MAX_OFFSET + 1);
+        SystemClockOffset.testWithOffset("System.currentTimeMillis()/1000 + MAX_OFFSET - 1",
+                System.currentTimeMillis()/1000 + MAX_OFFSET - 1);
+        SystemClockOffset.testWithOffset("System.currentTimeMillis()/1000 - MAX_OFFSET",
+                System.currentTimeMillis()/1000 - MAX_OFFSET);
+        SystemClockOffset.testWithOffset("System.currentTimeMillis()/1000 + MAX_OFFSET",
+                System.currentTimeMillis()/1000 + MAX_OFFSET);
+        SystemClockOffset.testWithOffset("System.currentTimeMillis()/1000 - MAX_OFFSET - 1024",
+                System.currentTimeMillis()/1000 - MAX_OFFSET - 1024);
+        SystemClockOffset.testWithOffset("System.currentTimeMillis()/1000 + MAX_OFFSET + 1024",
+                System.currentTimeMillis()/1000 + MAX_OFFSET + 1024);
+        SystemClockOffset.testWithOffset("0", 0);
+        SystemClockOffset.testWithOffset("-1", -1);
+        SystemClockOffset.testWithOffset("Integer.MAX_VALUE + System.currentTimeMillis()/1000",
+                ((long)Integer.MAX_VALUE) + System.currentTimeMillis()/1000);
+        SystemClockOffset.testWithOffset("System.currentTimeMillis()/1000 - Integer.MIN_VALUE",
+                System.currentTimeMillis()/1000 - Integer.MIN_VALUE);
+        SystemClockOffset.testWithOffset("Long.MAX_VALUE", Long.MAX_VALUE);
+        SystemClockOffset.testWithOffset("System.currentTimeMillis()/1000 - Long.MIN_VALUE",
+                (Long.MIN_VALUE + System.currentTimeMillis()/1000)*-1);
+    }
 }
--- a/test/java/time/test/java/util/TestFormatter.java	Wed Jan 28 09:23:41 2015 +0100
+++ b/test/java/time/test/java/util/TestFormatter.java	Wed Jan 28 17:48:59 2015 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -38,6 +38,7 @@
 import java.time.temporal.ChronoField;
 import java.time.temporal.TemporalQueries;
 import java.time.temporal.TemporalAccessor;
+import java.time.temporal.UnsupportedTemporalTypeException;
 
 import java.util.*;
 
@@ -153,6 +154,44 @@
         if (verbose) {
             System.out.printf("%-24s  : %s%n", getClassName(dt), out);
         }
+
+        // expected usually comes from Calendar which only has milliseconds
+        // precision. So we're going to replace it's N:[nanos] stamp with
+        // the correct value for nanos.
+        if ((dt instanceof TemporalAccessor) && expected != null) {
+            try {
+                // Get millis & nanos from the dt
+                final TemporalAccessor ta = (TemporalAccessor) dt;
+                final int nanos = ta.get(ChronoField.NANO_OF_SECOND);
+                final int millis = ta.get(ChronoField.MILLI_OF_SECOND);
+                final String nanstr = String.valueOf(nanos);
+                final String mistr = String.valueOf(millis);
+
+                // Compute the value of the N:[nanos] field that we expect
+                // to find in 'out'
+                final StringBuilder sb = new StringBuilder();
+                sb.append("N:[");
+                for (int i=nanstr.length(); i<9; i++) {
+                    sb.append('0');
+                }
+                sb.append(nanos).append("]");
+
+                // Compute the truncated value of N:[nanos] field that might
+                // be in 'expected' when expected was built from Calendar.
+                final StringBuilder sbm = new StringBuilder();
+                sbm.append("N:[");
+                for (int i=mistr.length(); i<3; i++) {
+                    sbm.append('0');
+                }
+                sbm.append(mistr).append("000000]");
+
+                // if expected contains the truncated value, replace it with
+                // the complete value.
+                expected = expected.replace(sbm.toString(), sb.toString());
+            } catch (UnsupportedTemporalTypeException e) {
+                // nano seconds unsupported - nothing to do...
+            }
+        }
         if (expected != null && !out.equals(expected)) {
             System.out.printf("%-24s  actual: %s%n                FAILED; expected: %s%n",
                               getClassName(dt), out, expected);
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/sun/misc/VM/GetNanoTimeAdjustment.java	Wed Jan 28 17:48:59 2015 +0100
@@ -0,0 +1,249 @@
+/*
+ * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+import java.util.Objects;
+import sun.misc.VM;
+
+/**
+ * @test
+ * @bug 8068730
+ * @summary tests that VM.getgetNanoTimeAdjustment() works as expected.
+ * @run main GetNanoTimeAdjustment
+ * @author danielfuchs
+ */
+public class GetNanoTimeAdjustment {
+
+    static final int MILLIS_IN_SECOND = 1000;
+    static final int NANOS_IN_MILLI = 1000_000;
+    static final int NANOS_IN_MICRO = 1000;
+    static final int NANOS_IN_SECOND = 1000_000_000;
+
+    static final boolean verbose = true;
+
+    static final class TestAssertException extends RuntimeException {
+        TestAssertException(String msg) { super(msg); }
+    }
+
+    private static void assertEquals(long expected, long received, String msg) {
+        if (expected != received) {
+            throw new TestAssertException("Unexpected result for " + msg
+                    + ".\n\texpected: " + expected
+                    +  "\n\tactual:   " + received);
+        } else if (verbose) {
+            System.out.println("Got expected " + msg + ": " + received);
+        }
+    }
+
+    private static void assertEquals(Object expected, Object received, String msg) {
+        if (!Objects.equals(expected, received)) {
+            throw new TestAssertException("Unexpected result for " + msg
+                    + ".\n\texpected: " + expected
+                    +  "\n\tactual:   " + received);
+        } else if (verbose) {
+            System.out.println("Got expected " + msg + ": " + received);
+        }
+    }
+
+    static final long MAX_OFFSET = 0x0100000000L;
+    static final long MIN_OFFSET = -MAX_OFFSET;
+    static enum Answer {
+        YES,   // isOffLimit = YES:   we must get -1
+        NO,    // isOffLimit = NO:    we must not not get -1
+        MAYBE  // isOffLimit = MAYBE: we might get -1 or a valid adjustment.
+    };
+    static long distance(long one, long two) {
+        return one > two ? Math.subtractExact(one, two)
+                : Math.subtractExact(two, one);
+    }
+
+
+    static Answer isOffLimits(long before, long after, long offset) {
+        long relativeDistanceBefore = distance(before, offset);
+        long relativeDistanceAfter  = distance(after, offset);
+        if (relativeDistanceBefore >= MAX_OFFSET && relativeDistanceAfter >= MAX_OFFSET) {
+            return Answer.YES;
+        }
+        if (relativeDistanceBefore < MAX_OFFSET && relativeDistanceAfter < MAX_OFFSET) {
+            if (relativeDistanceBefore == 0 || relativeDistanceAfter == 0) {
+                return Answer.MAYBE; // unlucky case where
+            }
+            return Answer.NO;
+        }
+        return Answer.MAYBE;
+    }
+
+    static void testWithOffset(String name, long offset) {
+        System.out.println("Testing with offset: " + name);
+        long beforeMillis = System.currentTimeMillis();
+        long adjustment = VM.getNanoTimeAdjustment(offset);
+        long afterMillis = System.currentTimeMillis();
+
+        if (offset >= beforeMillis/MILLIS_IN_SECOND
+                && offset <= afterMillis/MILLIS_IN_SECOND) {
+            if (adjustment == -1) {
+                // it's possible that we have fallen in the unlucky case
+                // where -1 was the genuine result. let's go backward a bit.
+                offset = offset - 10;
+                beforeMillis = System.currentTimeMillis();
+                adjustment = VM.getNanoTimeAdjustment(offset);
+                afterMillis = System.currentTimeMillis();
+                if (adjustment == -1) {
+                    throw new RuntimeException(name + ": VM says " + offset
+                            + " secs is too far off, "
+                            + " when time in seconds is in ["
+                            + beforeMillis/MILLIS_IN_SECOND + ", "
+                            + afterMillis/MILLIS_IN_SECOND
+                            + "]");
+                }
+            }
+        }
+
+        Answer isOffLimit = isOffLimits(beforeMillis/MILLIS_IN_SECOND,
+                afterMillis/MILLIS_IN_SECOND, offset);
+        switch (isOffLimit) {
+            case YES:
+                if (adjustment != -1) {
+                    throw new RuntimeException(name
+                        + ": VM should have returned -1 for "
+                        + offset
+                        + " when time in seconds is in ["
+                        + beforeMillis/MILLIS_IN_SECOND + ", "
+                        + afterMillis/MILLIS_IN_SECOND + "]");
+                }
+                System.out.println("Got expected exception value: " + adjustment);
+                break;
+            case NO:
+                if (adjustment == -1) {
+                    throw new RuntimeException(name
+                            + "VM says "  + offset
+                            + " secs is too far off, "
+                            + " when time in seconds is in ["
+                            + beforeMillis/MILLIS_IN_SECOND + ", "
+                            + afterMillis/MILLIS_IN_SECOND
+                            + "]");
+                }
+                break;
+            case MAYBE:
+                System.out.println("Adjustment: " + adjustment);
+                System.out.println("Can't assert for -1 with offset "
+                        + offset + "(" + name + ")"
+                        + " when time in seconds is in ["
+                        + beforeMillis/MILLIS_IN_SECOND + ", "
+                        + afterMillis/MILLIS_IN_SECOND
+                        + "]");
+                // not conclusive
+        }
+
+        if (isOffLimit == Answer.NO || adjustment != -1) {
+            System.out.println("Validating adjustment: " + adjustment);
+            long expectedMax = distance(offset, beforeMillis/MILLIS_IN_SECOND)
+                      * NANOS_IN_SECOND
+                    + (beforeMillis % MILLIS_IN_SECOND) * NANOS_IN_MILLI
+                    + (afterMillis - beforeMillis + 1) * NANOS_IN_MILLI;
+            long absoluteAdjustment = distance(0, adjustment);
+            if (absoluteAdjustment > expectedMax) {
+                long adjSec = absoluteAdjustment / NANOS_IN_SECOND;
+                long adjMil = (absoluteAdjustment % NANOS_IN_SECOND) / NANOS_IN_MILLI;
+                long adjMic = (absoluteAdjustment % NANOS_IN_MILLI) / NANOS_IN_MICRO;
+                long adjNan = (absoluteAdjustment % NANOS_IN_MICRO);
+                long expSec = expectedMax / NANOS_IN_SECOND;
+                long expMil = (expectedMax % NANOS_IN_SECOND) / NANOS_IN_MILLI;
+                long expMic = (expectedMax % NANOS_IN_MILLI) / NANOS_IN_MICRO;
+                long expNan = (expectedMax % NANOS_IN_MICRO);
+                System.err.println("Excessive adjustment: " + adjSec + "s, "
+                        + adjMil + "ms, " + adjMic + "mics, " + adjNan + "ns");
+                System.err.println("Epected max: " + expSec + "s, "
+                        + expMil + "ms, " + expMic + "mics, " + expNan + "ns");
+
+                throw new RuntimeException(name
+                    + ": Excessive adjustment: " + adjustment
+                    + " when time in millis is in ["
+                    + beforeMillis + ", " + afterMillis
+                    + "] and offset in seconds is " + offset);
+            }
+        }
+
+    }
+
+    static void regular() {
+        System.out.println("*** Testing regular cases ***");
+        final long start = System.currentTimeMillis();
+        long offset = start/1000;
+        long adjustment = VM.getNanoTimeAdjustment(offset);
+        if (start != offset*1000) {
+            if (adjustment == -1) {
+                throw new RuntimeException("VM says " + offset
+                        + " secs is too far off, but time millis is "
+                        + System.currentTimeMillis());
+            }
+        }
+        if (adjustment == -1) {
+            offset = System.currentTimeMillis()/1000 - 1024;
+            adjustment = VM.getNanoTimeAdjustment(offset);
+            if (adjustment == -1) {
+                throw new RuntimeException("VM says " + offset
+                        + " secs is too far off, but time millis is "
+                        + System.currentTimeMillis());
+            }
+        }
+        if (adjustment > (start/1000 - offset + 20)*NANOS_IN_SECOND) {
+            throw new RuntimeException("Excessive adjustment: " + adjustment);
+        }
+        testWithOffset("System.currentTimeMillis()/1000",
+                System.currentTimeMillis()/1000);
+        testWithOffset("System.currentTimeMillis()/1000 - 1024",
+                System.currentTimeMillis()/1000 - 1024);
+        testWithOffset("System.currentTimeMillis()/1000 + 1024",
+                System.currentTimeMillis()/1000 + 1024);
+    }
+
+    static void testLimits() {
+        System.out.println("*** Testing limits ***");
+        testWithOffset("System.currentTimeMillis()/1000 - MAX_OFFSET + 1",
+                System.currentTimeMillis()/1000 - MAX_OFFSET + 1);
+        testWithOffset("System.currentTimeMillis()/1000 + MAX_OFFSET - 1",
+                System.currentTimeMillis()/1000 + MAX_OFFSET - 1);
+        testWithOffset("System.currentTimeMillis()/1000 - MAX_OFFSET",
+                System.currentTimeMillis()/1000 - MAX_OFFSET);
+        testWithOffset("System.currentTimeMillis()/1000 + MAX_OFFSET",
+                System.currentTimeMillis()/1000 + MAX_OFFSET);
+        testWithOffset("System.currentTimeMillis()/1000 - MAX_OFFSET - 1024",
+                System.currentTimeMillis()/1000 - MAX_OFFSET - 1024);
+        testWithOffset("System.currentTimeMillis()/1000 + MAX_OFFSET + 1024",
+                System.currentTimeMillis()/1000 + MAX_OFFSET + 1024);
+        testWithOffset("0", 0);
+        testWithOffset("-1", -1);
+        testWithOffset("Integer.MAX_VALUE + System.currentTimeMillis()/1000",
+                ((long)Integer.MAX_VALUE) + System.currentTimeMillis()/1000);
+        testWithOffset("System.currentTimeMillis()/1000 - Integer.MIN_VALUE",
+                System.currentTimeMillis()/1000 - Integer.MIN_VALUE);
+        testWithOffset("Long.MAX_VALUE", Long.MAX_VALUE);
+        testWithOffset("System.currentTimeMillis()/1000 - Long.MIN_VALUE",
+                (Long.MIN_VALUE + System.currentTimeMillis()/1000)*-1);
+    }
+
+    public static void main(String[] args) throws Exception {
+        regular();
+        testLimits();
+    }
+
+}