Apparant bug in the JVM

[Alan Bateman]

I assume this is it:
   https://bugs.openjdk.java.net/browse/JDK-8027622

You need to use -XX:- XX:-UseMathExactIntrinsics until hs25-b58 makes it 
into a build.

-Alan.



On 11/11/2013 13:23, Stephen Colebourne wrote:
> I was sent this piece of test code by Dirk Lemmermann. It fails
> randomly on JDK8 b114
>
> import static java.time.temporal.ChronoUnit.DAYS;
> import java.time.Instant;
>
> public class TestInstantBug {
>          public static void main(String[] args) {
>                  Instant now = Instant.now();
>                  System.out.println("now = " + now);
>                  for (int i = 0; i<  100000; i++) {
>                          System.out.println(i);
>                          Instant truncated = now.truncatedTo(DAYS);
>                          System.out.println(truncated);
>                  }
>          }
> }
>
> The code does not change any variables during the loop. Instant is
> immutable and well written to my knowledge.
>
> My debugging shows some horrible behaviour.
>
> I copied Instant.java and edited it, adding it to the bootclasspath.
> This is the original code in Instant.java:
>      private static Instant create(long seconds, int nanoOfSecond) {
>          if ((seconds | nanoOfSecond) == 0) {
>              return EPOCH;
>          }
>          if (seconds<  MIN_SECOND || seconds>  MAX_SECOND) {
>              throw new DateTimeException("Instant exceeds minimum or
> maximum instant");
>          }
>          return new Instant(seconds, nanoOfSecond);
>      }
>
> The second if statement randomly fails.
> Worse, the use of a System.out.println() on the "seconds" variable
> causes the if statement to reset.
>
> Given this test code:
>
>      private static Instant create(long seconds, int nanoOfSecond) {
>          if ((seconds | nanoOfSecond) == 0) {
>              return EPOCH;
>          }
>          System.out.println(seconds<  MIN_SECOND || seconds>  MAX_SECOND);
>          if (seconds<  MIN_SECOND || seconds>  MAX_SECOND) {
>              System.out.println(MIN_SECOND);
>              System.out.println(MAX_SECOND);
>              System.out.println(seconds);
>              System.out.println(seconds<  MIN_SECOND);
>              System.out.println(seconds>  MAX_SECOND);
>              System.out.println(seconds<  MIN_SECOND || seconds>  MAX_SECOND);
>              System.out.println("Create " + seconds);
>              System.out.println(MIN_SECOND);
>              System.out.println(MAX_SECOND);
>              System.out.println(seconds);
>              System.out.println(seconds<  MIN_SECOND);
>              System.out.println(seconds>  MAX_SECOND);
>              System.out.println(seconds<  MIN_SECOND || seconds>  MAX_SECOND);
>              throw new DateTimeException("Instant exceeds minimum or
> maximum instant");
>          }
>          return new Instant(seconds, nanoOfSecond);
>      }
>
> the output is (when it actually fails):
> true   // the if statement randomly returned true
> -31557014167219200
> 31556889864403199
> 1384128000
> false  // the two parts of the if statement return false
> false  // the two parts of the if statement return false
> true   // the if statement still returns true
> Create 1384128000  // system out resets it
> -31557014167219200
> 31556889864403199
> 1384128000
> false
> false
> false   // the if statement returns false
> Exception in thread "main" java.time.DateTimeException: Instant
> exceeds minimum or maximum instant
>      at java.time.Instant.create(Instant.java:422)
>      at java.time.Instant.ofEpochSecond(Instant.java:327)
>      at java.time.Instant.plus(Instant.java:940)
>      at java.time.Instant.plusNanos(Instant.java:918)
>      at java.time.Instant.truncatedTo(Instant.java:773)
>      at TestInstantBug.main(TestInstantBug.java:13)
>      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
>      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
>      at java.lang.reflect.Method.invoke(Method.java:483)
>      at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)
>
> Hope you can squash this bug. b114 needs a big warning sign on it.
>
> Stephen