A new warning was recently introduced in the GC system by JDK-8071770:

[4.144s][warning][gc] Detected clock going backwards. Milliseconds since last GC would be -3828. returning zero instead.

This seems to happen frequently when running the sun/tools/jstatd tests on windows machines. The tests are matching output from the JVM and fail when they see this message.

We should investigate why the warning happens, and the tests should be updated to ignore it.


RULE "sun/tools/jstatd/TestJstatdExternalRegistry.java" Exception java.lang.RuntimeException: No or invalid headline found, expected: [S0 S1 E O M CCS YGC YGCT FGC FGCT GCT]: expected true, was false
RULE "sun/tools/jstatd/TestJstatdDefaults.java" Exception java.lang.RuntimeException: No or invalid headline found, expected: [S0 S1 E O M CCS YGC YGCT FGC FGCT GCT]: expected true, was false
RULE "sun/tools/jstatd/TestJstatdPort.java" Exception java.lang.RuntimeException: No or invalid headline found, expected: [S0 S1 E O M CCS YGC YGCT FGC FGCT GCT]: expected true, was false
RULE "sun/tools/jstatd/TestJstatdPortAndServer.java" Exception java.lang.RuntimeException: No or invalid headline found, expected: [S0 S1 E O M CCS YGC YGCT FGC FGCT GCT]: expected true, was false
RULE "sun/tools/jstatd/TestJstatdServer.java" Exception java.lang.RuntimeException: No or invalid headline found, expected: [S0 S1 E O M CCS YGC YGCT FGC FGCT GCT]: expected true, was false

RULE "sun/tools/jstatd/TestJstatdExternalRegistry.java" Exception java.lang.RuntimeException: Invalid number of data columns: [[...][warning][gc], Detected, clock, going, backwards., Milliseconds, since, last, GC, would, be, ..., returning, zero, instead., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...]: expected ... to equal ...
RULE "sun/tools/jstatd/TestJstatdServer.java" Exception java.lang.RuntimeException: Invalid number of data columns: [[...][warning][gc], Detected, clock, going, backwards., Milliseconds, since, last, GC, would, be, ..., returning, zero, instead., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...]: expected ... to equal ...
RULE "sun/tools/jstatd/TestJstatdDefaults.java" Exception java.lang.RuntimeException: Invalid number of data columns: [[...][warning][gc], Detected, clock, going, backwards., Milliseconds, since, last, GC, would, be, ..., returning, zero, instead., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...]: expected ... to equal ...
RULE "sun/tools/jstatd/TestJstatdPort.java" Exception java.lang.RuntimeException: Invalid number of data columns: [[...][warning][gc], Detected, clock, going, backwards., Milliseconds, since, last, GC, would, be, ..., returning, zero, instead., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...]: expected ... to equal ...
RULE "sun/tools/jstatd/TestJstatdPortAndServer.java" Exception java.lang.RuntimeException: Invalid number of data columns: [[...][warning][gc], Detected, clock, going, backwards., Milliseconds, since, last, GC, would, be, ..., returning, zero, instead., ..., ..., ..., ..., ..., ..., ..., ..., ..., ..., ...]: expected ... to equal ...

RULE "sun/tools/jstatd/TestJstatdPort.java" Exception java.lang.RuntimeException: Output does not match the pattern [...][warning][gc] Detected clock going backwards. Milliseconds since last GC would be ... returning zero instead. ... Jps: expected true, was false